Radiant Barrier DIY

[03trubluGT]

I just ordered 2k sq ft of radiant barrier from :

http://www.atticfoil.com/index.html

$265.39 shipped (including tax)


I'll post up some pics of the install when I get around to it. I'll have to get up freaking early to start this project since it's too damn hot to do it in the late morning/afternoon...

[bcoop]

Best bet is to do it when it's dark, it's a hot mother fucker up there. Hope you have plenty of drop lights!

[propellerhead]

Interesting. I've been thinking of doing that to at least the south and west facing roof.

Subscribing...

[Sgt Beavis]

I just ordered 2k sq ft of radiant barrier from :

http://www.atticfoil.com/index.html

$265.39 shipped (including tax)


I'll post up some pics of the install when I get around to it. I'll have to get up freaking early to start this project since it's too damn hot to do it in the late morning/afternoon...

Be sure to detail how you install around roof openings and vents.

Subscribing...

[Sgt Beavis]

Best bet is to do it when it's dark, it's a hot mother fucker up there. Hope you have plenty of drop lights!

That website has some advice about that.

http://www.atticfoil.com/radiant%20barrier%20trick.htm

[ClockwrkOrangeS4]

Best bet is to do it when it's dark, it's a hot mother fucker up there. Hope you have plenty of drop lights!

Fuck that man, wait til fall.

[DFWtechie]

Why didn't you just go pick it up? They are in Dallas with a pick up station in Richardson.

[03trubluGT]

Best bet is to do it when it's dark, it's a hot mother fucker up there. Hope you have plenty of drop lights!


That's why I said I'd start early (4am or so). That should be about as cool as it's gonna get. The radiant heat from the day should be dissapated by then, and I'll have a few hours before the sun comes up.

[03trubluGT]

Fuck that man, wait til fall.


I thought about it, but after seeing my electricity bills climb, I'm not gonna wait.

[03trubluGT]

Why didn't you just go pick it up? They are in Dallas with a pick up station in Richardson.


I'm in Mansfield. By the time I drive from home to Richardson and back considering my time and fuel, it's worth the $17 for UPS to bring it to me....

[2165 Turbo Rail]

subscribing too

I'm going to be installing the attic fans with a thermostat to evacuate the hot air and I'm going to block off the garage from the house attic space.. because right now the garage isn't insulated at all... and the house is insulated to hell but there is a big ass opening between to the two areas
has anyone else done something similar to what I am talking about (blocking off the garage from the house)

[Txstang1]

<----subscribing

[wesman]

Hrmmmm....interested in seeing how this goes.....best of luck.

--wes

[03trubluGT]

subscribing too

I'm going to be installing the attic fans with a thermostat to evacuate the hot air and I'm going to block off the garage from the house attic space.. because right now the garage isn't insulated at all... and the house is insulated to hell but there is a big ass opening between to the two areas
has anyone else done something similar to what I am talking about (blocking off the garage from the house)


I had 2 large electric attic fans. I opted to not put them back when I had my roof redone.

I had ridge vents and whirly birds installed instead. Now I don't have to pay to run 2 fans.

[bcoop]

That website has some advice about that.

http://www.atticfoil.com/radiant%20barrier%20trick.htm




Perfect solution, that's what I'd do. Can't beat that with a stick!


Subscribing as well. I'd like to see results on energy savings, and difficulty of installation.

[bcoop]

I had 2 large electric attic fans. I opted to not put them back when I had my roof redone.

I had ridge vents and whirly birds installed instead. Now I don't have to pay to run 2 fans.


You could have just set the second fan on a thermostat. Once it hits a certain temp, it cuts on. And when it cools to a certain temp, it cuts back off.


Whirly birds are the fucking suck. I'll probably be going solar...

[2165 Turbo Rail]

You could have just set the second fan on a thermostat. Once it hits a certain temp, it cuts on. And when it cools to a certain temp, it cuts back off.


Whirly birds are the fucking suck. I'll probably be going solar...


that's what I was going to do it have them set at a certain temp and the second one could comeo n about 5* higher or something

[Red 342 H.O.]

Fuck that man, wait til fall.
I am waiting until fall to do mine. Meanwhile I am taking temp avg. in my attic, garage and in the house this summer so I can see the difference next summer. Guy at work did it and he said it reduced his attic temp from about 140 to less than 100.

I am interested on how the install goes so keep us posted.

[Sgt Beavis]

Perfect solution, that's what I'd do. Can't beat that with a stick!


Subscribing as well. I'd like to see results on energy savings, and difficulty of installation.

Its one of those, "why the fuck didn't I think of that" solutions. So friggin simple and obvious but no one thinks of it...

[Vertnut]

I am waiting until fall to do mine. Meanwhile I am taking temp avg. in my attic, garage and in the house this summer so I can see the difference next summer. Guy at work did it and he said it reduced his attic temp from about 140 to less than 100.

I am interested on how the install goes so keep us posted.
From my experience, it's good for about a 30 degree difference in mid-summer, depending on the layout of your attic, roof pitch, etc.

[propellerhead]

The question is... will a drop in attic temp really make a difference? I know that's a never ending debate. I guess it depends on how well your attic and ducts are insulated.

[Vertnut]

The question is... will a drop in attic temp really make a difference? I know that's a never ending debate. I guess it depends on how well your attic and ducts are insulated.
"Big Studly" says no. He's an engineer, I believe, and with my son-in-law being one, I know you can't tell 'em shit. ;) I think the main reason it works for the A/C, is because the air ducts are moving cold air through them and it's 140 degree's around those ducts. The air will stay colder in the ducts if the temperature around them is 30-35 degree's cooler. Just know that from October till March, a radiant barrier of any sort, won't have much effect.

[ceyko]

The question is... will a drop in attic temp really make a difference? I know that's a never ending debate. I guess it depends on how well your attic and ducts are insulated.

I have no real measurements other than my computer room. This year I forgot to turn on my attic fan (w/ thermostat). My room up stairs would see 93/94 degrees and it is insulated well. Now that I've turned it on my room does not see anything above 80 degrees.

I have a single door that is sealed well to the attic, so my scenario is a little different that a standard house with an attic above it. But it seems that attic temperatures do make a difference.

edit: I'm thinking more from the angle of radiant heat in the attic sort of making the interior walls hotter - even with insulation.

[propellerhead]

It's probably a function of the insulation around the ducts and attic. If you have a light jacket on, you'll feel a 10* drop in ambient temperature. With a thick winter coat on, you won't notice it.

[03trubluGT]

that's what I was going to do it have them set at a certain temp and the second one could comeo n about 5* higher or something


I had mine staggered so one would come on at 90-95 and the other at about 100-105. The thing was the fan that was set at the lower temp never shut off when the sun was out. If I did it all again, I'd set both of them at 95 and just leave it alone.

[03trubluGT]

I made it home today from my part time job at 12:25 and the radiant barrier was on my porch ;)

I ordered this stuff yesterday at about 10am and it was here by noon-ish the next day. Now that's what I call service!!!


The bad news is now I have to put crap up!!! :mad:

[Red 342 H.O.]

I made it home today from my part time job at 12:25 and the radiant barrier was on my porch ;)

I ordered this stuff yesterday at about 10am and it was here by noon-ish the next day. Now that's what I call service!!!


The bad news is now I have to put crap up!!! :mad:

Pictures and progress when you get a chance.

[jyro]

subscribing too

I'm going to be installing the attic fans with a thermostat to evacuate the hot air and I'm going to block off the garage from the house attic space.. because right now the garage isn't insulated at all... and the house is insulated to hell but there is a big ass opening between to the two areas
has anyone else done something similar to what I am talking about (blocking off the garage from the house)

I think that would be a waste of time

[jyro]

I have no real measurements other than my computer room. This year I forgot to turn on my attic fan (w/ thermostat). My room up stairs would see 93/94 degrees and it is insulated well. Now that I've turned it on my room does not see anything above 80 degrees.

I have a single door that is sealed well to the attic, so my scenario is a little different that a standard house with an attic above it. But it seems that attic temperatures do make a difference.

edit: I'm thinking more from the angle of radiant heat in the attic sort of making the interior walls hotter - even with insulation.

insulation heat transfer is based on a calculation using the difference in temperature of both sides of the insulation. Lower the heat in the attic, you reduce the transfer to the other side.
http://www.engineeringtoolbox.com/conductive-heat-transfer-d_428.html

This temperature difference on the two sides of a surface, say an insulated building wall, for example, is very important in understanding how a building loses heat (in the heating season) or gains heat (in the cooling season). That's because the rate of heat transfer through a material increases exponentially as a function of the temperature difference. This is intuitively obvious and is confirmed by physicists. For example, if the temperatures on either side of a building wall were the same, there would be no heat loss or gain through the building wall. As the temperature difference on either side of that same wall increases, say from one degree of difference to 20 degrees of difference the rate of heat transfer increases. http://www.inspect-ny.com/interiors/Heat-Loss-In-Buildings.htm

[ceyko]

So, you're confirming that a hot attic will make a difference. I was trying to stay neutral in my post above, but I'm sold on it as well.

IMO heat in the attic is no different than a burner on a pot. With the burner on, stuff on the inside of a pot would get hot. If you were to insulate a pot one way or another, it would still get hot inside but it may take longer and it may not be as proportional to the heat source.

Fans, insulation and such help reduce heat in the attic. However, other radiant barrier threads indicated that it was less effective on well insulated homes - but hell - it can't hurt for 250 buck and some labor. (well, a lot of labor)

[Kenny_Stang]

Any of you guys heard that putting Radiant Barrier could cause you to have to replace your roof within a couple of years? According to our HVAC guy, Radiant Barrier works great, but during the summer the heat it reflects back on to the roof could cause you to have to redo your roof shingles every few years... he recommended attic fans over radiant barrier.

[Mustangman_2000]

Interesting. I'll be interested to see how it affects your attic temps.

[wade_racing]

another option that a guy at work just did it seems to be working great he said its about 50 degrees cooler in his attic now... dropped it from just over 150 down to just over 100 according to him.

http://koolcoat.com/

you can add it to any paint...

[propellerhead]

Any of you guys heard that putting Radiant Barrier could cause you to have to replace your roof within a couple of years? According to our HVAC guy, Radiant Barrier works great, but during the summer the heat it reflects back on to the roof could cause you to have to redo your roof shingles every few years... he recommended attic fans over radiant barrier.
That's what I'm worried about. Same reasons window tint should be put on the outside of double pane windows.

[Red 342 H.O.]

I am not a believer in the spray on silver stuff stuff but KoolCoat might be helpful.

[03trubluGT]

Any of you guys heard that putting Radiant Barrier could cause you to have to replace your roof within a couple of years? According to our HVAC guy, Radiant Barrier works great, but during the summer the heat it reflects back on to the roof could cause you to have to redo your roof shingles every few years... he recommended attic fans over radiant barrier.


From the research I've done, the radiant board (the stuff that's on the back of the roofing plywood) and the spray on is the worst for shingles. The sun heats up the shingles, transfers to the tar paper, then the wood and then is reflected back up in reverse order. With the attic foil, the same process occurs, but the heat then goes into the 3.5" space to the foil, and is then directed up to the ridge vents/passive vents/whirly birds or whatever else you have.

I found a website that says the best way to install radiant barrier is to overlay the insulation, but I'm wanting to reduce the attic temp so my AC unit doesn't have to work so hard.

[03trubluGT]

I've been busy pulling up the scraps of shit they used to deck under my AC units. It looks like they just scabbed pieces of wood together and it looks like crap. There are places where the plywood is 4 layers thick!

I started to redeck with pressure treated 1x6x8 boards because I can't get sheets of plywood up my attic access.

I did however get to apply the radiant barrier to the east wall above my garage. it took about 45 minutes to do a 16'x48" piece and then about a 8'x48" above it.

This stuff is VERY easy to put up, and being 5mil thick it stays put well so you can use the staple gun to attach it.

The bad thing is that it is VERY LABOR INTENSIVE, and it's gonna suck doing the whole house by myself. My wife is a klutz and there's no way I'm gonna have her up there. I'll be replacing sheet rock if she goes up, and paying an ER visit.

I'll try to get some done tomorrow and post a before/after pic.

[Mixedup]

I am not a believer in the spray on silver stuff stuff but KoolCoat might be helpful.


Sherman Williams spray on stuff in my attic - outside temp right now is 102 ... my attic is 110.7 ..... I think the stuff works ..... plus I have one power attic fan on thermostat

[Red 342 H.O.]

Sherman Williams spray on stuff in my attic - outside temp right now is 102 ... my attic is 110.7 ..... I think the stuff works ..... plus I have one power attic fan on thermostat

Guess I shouldn't knock it until I try it. But I think I am going to go with the material and do it myself this fall. Guy that insulated my attic quoted me $2650 to do my attic witrh the spray stuff and he said it would take and hour or two to do. :eek:

Material will cost me about $300 or less and some of my time and risk of falling through the ceiling............ ;)

If someone can spray mine in and do it for less than $500 then I am on board.

[Mixedup]

Guess I shouldn't knock it until I try it. But I think I am going to go with the material and do it myself this fall. Guy that insulated my attic quoted me $2650 to do my attic witrh the spray stuff and he said it would take and hour or two to do. :eek:

Material will cost me about $300 or less and some of my time and risk of falling through the ceiling............ ;)

If someone can spray mine in and do it for less than $500 then I am on board.


Two 5 gal pails cost me almost $500 - and for the painting I talked to a paint crew that was working on some new homes and they "moonlighted" and painted my attic - poor guy was hotter than hell and came out looking like a silver alien - I think I gave him 400 to apaint it - total of 900 in cost and I was able to deduct some of the costs from my taxes too!

[Vertnut]

Any of you guys heard that putting Radiant Barrier could cause you to have to replace your roof within a couple of years? According to our HVAC guy, Radiant Barrier works great, but during the summer the heat it reflects back on to the roof could cause you to have to redo your roof shingles every few years... he recommended attic fans over radiant barrier.
Never heard that, and I've been using it exclusively in all my new homes for the past 4 years. My roofing company says it's not an issue (I use a 30 year shingle), and I've had nothing but positive feedback and results. I've got houses out there four years old with it, and no issues or complaint's...

[the spindoctor]

even if it doesn't affect the life of the roof, i'm guessing that it would work better at holding the heat in during the winter, too if its on the attic floor instead of the roof. and you don't need nearly as much of it.

[Red 342 H.O.]

Two 5 gal pails cost me almost $500 - and for the painting I talked to a paint crew that was working on some new homes and they "moonlighted" and painted my attic - poor guy was hotter than hell and came out looking like a silver alien - I think I gave him 400 to apaint it - total of 900 in cost and I was able to deduct some of the costs from my taxes too!

LMAO.....silver alien. :D

[03trubluGT]

LMAO.....silver alien. :D


It went right over my head until I read your post..... :D :D :D

[Tx Redneck]

The object of laying over insulation versus spraying on the back of the roof deck is so you don't cool the attic in the summer and heat it in the winter. The very best thing you can do is install continuous ridge vent w/ soffet vents accordingly and let nature do the work. Withe the roof pitch and the heating effect of the attic it makes a suction drawing the heat out through the ridge vents and fresh cool air in through the soffet. With the addition of RB over the insulation it magnifies the effect. If you have whirly birds take them out or block them off and do ridge/soffet as whirly birds create hot spots. If anyone has any REAL questions regarding this I might be able to put you in touch w/ my dad as he's internationally certified for commercial/res. inspections and has been in the industry for 30+ years.

[2165 Turbo Rail]

The object of laying over insulation versus spraying on the back of the roof deck is so you don't cool the attic in the summer and heat it in the winter. The very best thing you can do is install continuous ridge vent w/ soffet vents accordingly and let nature do the work. Withe the roof pitch and the heating effect of the attic it makes a suction drawing the heat out through the ridge vents and fresh cool air in through the soffet. With the addition of RB over the insulation it magnifies the effect. If you have whirly birds take them out or block them off and do ridge/soffet as whirly birds create hot spots. If anyone has any REAL questions regarding this I might be able to put you in touch w/ my dad as he's internationally certified for commercial/res. inspections and has been in the industry for 30+ years.

I posted a thread about KoolCoat and I talked about the Cor-A-Vent.com guys.. the continuous ridge vent set up they have.. looks like a great idea but Man! what a lot of work on an existing home! :eek:

[03trubluGT]

Now that I've got my electric bill figured out, since it's about 125 degrees up there during the day, I'm going to do a little at a time until it cools off some.

I'm gonna work on it a little (probably an hour or so) this afternoon and post up a pic.

[2165 Turbo Rail]

I've been running "test" this week and i found that my attic was getting to about 132 during the day. I put in one of those attic exhaust fans in and now its down to about 119 during the day That is the ONLY thing I did up there so far so 10* isn't much but for 80 bucks its a start

I kind of cheated .. i bought a gable fan and made it force air out of the existing whirlie bird in the roof. Then I got on the roof and the whirlie bird was going about 100mph! I stopped it and secured it so it wouldn't spin (this seemed to make the air come out better then when it was spinning)
The reason I did it this way..
Gable fan -$79 plus a few screws and 10 mins in the attic mounting it and wiring it in, 5 mins on the roof

true attic exhaust fan - $125 more time in the 130* attic and more time on the roof taking out the old whirlie bird and replacing it with the new fan

[Vertnut]

I've been running "test" this week and i found that my attic was getting to about 132 during the day. I put in one of those attic exhaust fans in and now its down to about 119 during the day That is the ONLY thing I did up there so far so 10* isn't much but for 80 bucks its a start

I kind of cheated .. i bought a gable fan and made it force air out of the existing whirlie bird in the roof. Then I got on the roof and the whirlie bird was going about 100mph! I stopped it and secured it so it wouldn't spin (this seemed to make the air come out better then when it was spinning)
The reason I did it this way..
Gable fan -$79 plus a few screws and 10 mins in the attic mounting it and wiring it in, 5 mins on the roof

true attic exhaust fan - $125 more time in the 130* attic and more time on the roof taking out the old whirlie bird and replacing it with the new fan
Hopefully, the electricity used for the fan doesn't off-set the 10* difference you gained. It's hard to pin down every dime.

[2165 Turbo Rail]

Hopefully, the electricity used for the fan doesn't off-set the 10* difference you gained. It's hard to pin down every dime.
thats what I'll be finding out on the next elec bill I guess... There are more things to come but I'm going to do them in stages This just happen to be the cheapest and quickest install

[blkscorpion80]

Now that I've got my electric bill figured out, since it's about 125 degrees up there during the day, I'm going to do a little at a time until it cools off some.

I'm gonna work on it a little (probably an hour or so) this afternoon and post up a pic.

So hows the install going? Where are the pics? Its a good thing you live in my neck of the woods (it won't be far for you to come and help me put mine up). I also live in Mansfield and would like to come and check it out, if you don't mind.

[BlackSnake1996]

Stay cool up there. You can always pull a AC duct and face it towards ya.

[03trubluGT]

So hows the install going? Where are the pics? Its a good thing you live in my neck of the woods (it won't be far for you to come and help me put mine up). I also live in Mansfield and would like to come and check it out, if you don't mind.


I'm going to work on it some more in the morning. I'll take some pics then and post up at lunch..

[GRAYHORSE]

subscribing too

I'm going to be installing the attic fans with a thermostat to evacuate the hot air and I'm going to block off the garage from the house attic space.. because right now the garage isn't insulated at all... and the house is insulated to hell but there is a big ass opening between to the two areas
has anyone else done something similar to what I am talking about (blocking off the garage from the house)


Your attic fans will do 10X's what the radiant barrier will do. If you get the good ones that is. It will be same temp in your attic as outside.

[2165 Turbo Rail]

Your attic fans will do 10X's what the radiant barrier will do. If you get the good ones that is. It will be same temp in your attic as outside.
I installed 1 and it dropped the temp to about 15* about outside temp (it was about 35 to 40* above outside temp.. so just the one helped a bunch..

I might put in another one when I get back home just because the one works great but I'm sure 2 would be more efficient.

[Vertnut]

Your attic fans will do 10X's what the radiant barrier will do. If you get the good ones that is. It will be same temp in your attic as outside.
It will never be the same temp in the attic during the hot summer. You just can't create the airflow needed to do that. Powered fans don't run for free, either.

[Big Studly]

It will never be the same temp in the attic during the hot summer. You just can't create the airflow needed to do that. Powered fans don't run for free, either.

not only in the hot summer, but NEVER. The equation for ventilaton has the temperature diffirential in the denominator, if the delta T is zero (same temp inside as outside), the solution becomes infinity. For straight ventilation I ususally use a delta T of 20*, but that is mainly for equipment rooms and such. I just designed the ventilation for a building with 3 7.5 hp vacuum pumps, 2 15 hp compressors and one refrigerated dryer and it needed 8500 CFM of ventilation to keep it to 120* max in the summer. A pump house I was doing with a 550 hp pump motor and a 5 hp air compressor needed around 15,000 CFM for a 10* delta T.

[Chopped54]

It will never be the same temp in the attic during the hot summer. You just can't create the airflow needed to do that. Powered fans don't run for free, either.


What about the solar powered ones?
Does the savings really outweigh the initial cost?

[Vertnut]

What about the solar powered ones?
Does the savings really outweigh the initial cost?
I'm not sure of the cost of the solar units. The cost of them used to be prohibitive for someone wanting to actually save money. I'm sure they've come down in price over the last few years, but I do know that solar panels themselves are pretty damned expensive.

*edit* Chopped54, I did a quick google, and it looks like you can buy one of the solar units for about $250. It says it would handle about 1500 sq.ft. of attic space.
A fair sized home would need 2, especially here in the Texas heat.

[Chopped54]

I'm not sure of the cost of the solar units. The cost of them used to be prohibitive for someone wanting to actually save money. I'm sure they've come down in price over the last few years, but I do know that solar panels themselves are pretty damned expensive.

*edit* Chopped54, I did a quick google, and it looks like you can buy one of the solar units for about $250. It says it would handle about 1500 sq.ft. of attic space.
A fair sized home would need 2, especially here in the Texas heat.

Where are homes most exposed to heat soak?
Attic??
Walls??

The attic is about 14-16" of depth to the insulation.


I ask because I am in an unincoporated part of Rockwall, and I know we did not have inspection/code enforcement.
I feel that the house is hotter then it should be, and the ac is working harder then it should.

[Vertnut]

The attic is your primary concern. Walls have brick (or stucco), or some type of outer facade, sheetrock inside, and hopefully, some internal batting, or insulation. Up top, you have shingles (usually an asphalt product), "felt" or maybe tar-paper (asphalt product), then roof deck. Where does the sun hit directly more than anywhere else on the house? You got it. 14"-16" is fine for Texas. Check your HVAC unit for tonnage vs. the size of your home. Check the ducts up in the attic for leak, especially if it's an older home. Check your window and door seals, because these can be huge culprits because there are so many of them. Maybe have the HVAC unit checked out good. I had a blower motor going out on a unit for a long time, and never knew it. Hope this at least gives you some ideas.

[Big Studly]

The attic is your primary concern. Walls have brick (or stucco), or some type of outer facade, sheetrock inside, and hopefully, some internal batting, or insulation. Up top, you have shingles (usually an asphalt product), "felt" or maybe tar-paper (asphalt product), then roof deck. Where does the sun hit directly more than anywhere else on the house? You got it. 14"-16" is fine for Texas. Check your HVAC unit for tonnage vs. the size of your home. Check the ducts up in the attic for leak, especially if it's an older home. Check your window and door seals, because these can be huge culprits because there are so many of them. Maybe have the HVAC unit checked out good. I had a blower motor going out on a unit for a long time, and never knew it. Hope this at least gives you some ideas.

something you should mention about how HVAC systems are sized for homes...for the most part, they are based on a rule of thumb, and that is an industry standard. That industry standard holds the same for homes in Texas, and homes in Michigan. I don't know where the rule of thumb (500 sq. ft. per ton) originated, but I would imagine it wasn't in a place that saw several weeks of 100+ summer heat. With that said, it stands to reason that during the dog days of summer everyones a/c unit will struggle if you live in a climate with extreme triple digit numbers. It is just something people in this region have to understand and get used to. Hell, when we size comercial or industiral HVAC systems, we base the design, not on the most extreme worst case, but that it only covers 99.4% of the days of the year....sometimes only 99%. For this area, the 99.4% ASHRAE temperature given in ASHRAE Fundamentals handbook 2008 is only 100F, so every day that is over 100F, the HVAC system is "undersized". It is just the way it is. For someone in Texas to complain that their system is struggling makes me laugh, because hell yes it does, it is 100+ outside. Not to mention the tonnage ratings of regular direct expansion units are based on something around 85F, so every degree above that, you actually lose efficiency of your unit. Add that to it not being sized for the conditions we see here in the dog days of summer, well, your a/c will run all the time and might not cool your house.

hate to break the news to you, but unless you want be oversized for the rest of the year...causing other problems, most of which would be cost related, then you just have to deal with it. I think the alternative is worse.

[Vertnut]

something you should mention about how HVAC systems are sized for homes...for the most part, they are based on a rule of thumb, and that is an industry standard. That industry standard holds the same for homes in Texas, and homes in Michigan. I don't know where the rule of thumb (500 sq. ft. per ton) originated, but I would imagine it wasn't in a place that saw several weeks of 100+ summer heat. With that said, it stands to reason that during the dog days of summer everyones a/c unit will struggle if you live in a climate with extreme triple digit numbers. It is just something people in this region have to understand and get used to. Hell, when we size comercial or industiral HVAC systems, we base the design, not on the most extreme worst case, but that it only covers 99.4% of the days of the year....sometimes only 99%. For this area, the 99.4% ASHRAE temperature given in ASHRAE Fundamentals handbook 2008 is only 100F, so every day that is over 100F, the HVAC system is "undersized". It is just the way it is. For someone in Texas to complain that their system is struggling makes me laugh, because hell yes it does, it is 100+ outside. Not to mention the tonnage ratings of regular direct expansion units are based on something around 85F, so every degree above that, you actually lose efficiency of your unit. Add that to it not being sized for the conditions we see here in the dog days of summer, well, your a/c will run all the time and might not cool your house.

hate to break the news to you, but unless you want be oversized for the rest of the year...causing other problems, most of which would be cost related, then you just have to deal with it. I think the alternative is worse.
The "rule of thumb" is just that. Our HVAC folks engineer the system from our plans, but still make mistakes on the distribution end of it. I don't know about his case, but ceiling height in houses can make a huge difference. As an engineer, you know there's more to HVAC than just square footage. Some of the "foam insulation" homes are using 1 ton per thousand feet of living space! I haven't used the high-density foam yet, because I'm a little concerned about some reports of it making the houses too tight, and allowing a better chance for mold to occur down the road.

[03trubluGT]

I'm going to work on it some more in the morning. I'll take some pics then and post up at lunch..


Sorry, I didn't get to work on it. I was going to the morning the thunderstorms rolled through, but we lost power and I couldn't work in the dark.

[03trubluGT]

not only in the hot summer, but NEVER. The equation for ventilaton has the temperature diffirential in the denominator, if the delta T is zero (same temp inside as outside), the solution becomes infinity. For straight ventilation I ususally use a delta T of 20*, but that is mainly for equipment rooms and such. I just designed the ventilation for a building with 3 7.5 hp vacuum pumps, 2 15 hp compressors and one refrigerated dryer and it needed 8500 CFM of ventilation to keep it to 120* max in the summer. A pump house I was doing with a 550 hp pump motor and a 5 hp air compressor needed around 15,000 CFM for a 10* delta T.

WhAt thE FaWk dID YoU sAY??????

[03trubluGT]

OK, been lazy, but at least here's a pic. One side over my garage is done, the other side isn't because it's gonna be a total PITA. It's where all my wires go to my electric service, cable, internet, etc......


The top is left undone the uppermost 6-8" so the heated air can travel up and out of the ridge vent.

[Tx Redneck]

OK, been lazy, but at least here's a pic. One side over my garage is done, the other side isn't because it's gonna be a total PITA. It's where all my wires go to my electric service, cable, internet, etc......


The top is left undone the uppermost 6-8" so the heated air can travel up and out of the ridge vent.
Doin' it that way, you mat as well have done the spray on and saved some money. The reason you lay the "foil" type over the insulation is to keep the heat outta the house and in the attic. By doing it the way it makes the ridge/soffet vents work that much better and uses less material.

[03trubluGT]

Doin' it that way, you mat as well have done the spray on and saved some money. The reason you lay the "foil" type over the insulation is to keep the heat outta the house and in the attic. By doing it the way it makes the ridge/soffet vents work that much better and uses less material.


I priced spray on and it looked to be about $2,500.

I can do the entire attic myself in foil for $650. Besides, I wanted to keep the heat out of the attic so my central air units didn't have to wallow in 130 degree temps.

I'm going back in after the foil is done and put about 20-30 more bags of blow in insulation up there.

[Red 342 H.O.]

I priced spray on and it looked to be about $2,500.

I can do the entire attic myself in foil for $650. Besides, I wanted to keep the heat out of the attic so my central air units didn't have to wallow in 130 degree temps.

I'm going back in after the foil is done and put about 20-30 more bags of blow in insulation up there.

THat is what I am going to do.....guess I can start buying a roll or two of the stuff and start here pretty soon. Lowe's has the stuff.....wonder if it is the same thing as you have.......you got it from Dallas, right?

[Tx Redneck]

I priced spray on and it looked to be about $2,500.

I can do the entire attic myself in foil for $650. Besides, I wanted to keep the heat out of the attic so my central air units didn't have to wallow in 130 degree temps.

I'm going back in after the foil is done and put about 20-30 more bags of blow in insulation up there.

W/ the soffet/ridge vent combo the attic will not get that hot. Besides that, you can wrap the unit if you were worried about it.

[Big Studly]

The "rule of thumb" is just that. Our HVAC folks engineer the system from our plans, but still make mistakes on the distribution end of it. I don't know about his case, but ceiling height in houses can make a huge difference. As an engineer, you know there's more to HVAC than just square footage. Some of the "foam insulation" homes are using 1 ton per thousand feet of living space! I haven't used the high-density foam yet, because I'm a little concerned about some reports of it making the houses too tight, and allowing a better chance for mold to occur down the road.

that is the exact reason I am very, VERY skeptical of the radiant barrier. In theory, yes, it should help, but since most homes do not have an engineered system, for these companies to blanketly say that a radiant barrier will save 30% off of your electric bill is preposterous. There are way too many variables for that to be a fact for everyone, which is why I still think adding more insulation to an existing home is the way to go. It is less labor intensive and will most likely yield the same results in the long run.

[03trubluGT]

W/ the soffet/ridge vent combo the attic will not get that hot. Besides that, you can wrap the unit if you were worried about it.


That's what I thought when I had the roof re-done, but the temps were still ranging in the 130-135 range. The roofers came back out and added 2 whirly birds and it dropped 15-20 degrees.

If I can drop the under roof temp as much as possible, I would think I have to be helping the AC units.

[03trubluGT]

that is the exact reason I am very, VERY skeptical of the radiant barrier. In theory, yes, it should help, but since most homes do not have an engineered system, for these companies to blanketly say that a radiant barrier will save 30% off of your electric bill is preposterous. There are way too many variables for that to be a fact for everyone, which is why I still think adding more insulation to an existing home is the way to go. It is less labor intensive and will most likely yield the same results in the long run.


That's why I'll be adding more after I get the foil done.

[03trubluGT]

THat is what I am going to do.....guess I can start buying a roll or two of the stuff and start here pretty soon. Lowe's has the stuff.....wonder if it is the same thing as you have.......you got it from Dallas, right?


I got it from www.atticfoil.com

I ordered it one morning at about 10am and it was on my porch the next day by noon.

It was WELL worth the $17 shipping to save me from driving from Mansfield to Richardson and back.

[justinsn95]

The question is... will a drop in attic temp really make a difference? I know that's a never ending debate. I guess it depends on how well your attic and ducts are insulated.

That's a good point... will it actually help anything at all? I guess if you see your electric bill take a $30 dive you know it helped. Well hell, if nothing else reducing your temps from 140 to 100 - you are getting at least a tiny degree further away from an attic fire...

[Vertnut]

that is the exact reason I am very, VERY skeptical of the radiant barrier. In theory, yes, it should help, but since most homes do not have an engineered system, for these companies to blanketly say that a radiant barrier will save 30% off of your electric bill is preposterous. There are way too many variables for that to be a fact for everyone, which is why I still think adding more insulation to an existing home is the way to go. It is less labor intensive and will most likely yield the same results in the long run.
Just for the record, all of my HVAC is engineered for each individual house, taking all factors into consideration.

[Big Studly]

Just for the record, all of my HVAC is engineered for each individual house, taking all factors into consideration.

what kind of units do you usually put in? I would assume a DX unit, but does it ever have any controls like a hot gas bypass or an economizer that is controlled by enthalpy? I don't know much about residential systems, do they even make that kind of stuff in the small units?

[Vertnut]

what kind of units do you usually put in? I would assume a DX unit, but does it ever have any controls like a hot gas bypass or an economizer that is controlled by enthalpy? I don't know much about residential systems, do they even make that kind of stuff in the small units?
Not typically, but I've done a few. HVAC tech stuff gets over my head pretty quickly, so I don't remember details. Our common systems are 14-seer Carrier Heat-pump units that use the "new" coolant. I also like using the large filters in the attic instead of the ones located at the return air grates.

[Big Studly]

Not typically, but I've done a few. HVAC tech stuff gets over my head pretty quickly, so I don't remember details. Our common systems are 14-seer Carrier Heat-pump units that use the "new" coolant. I also like using the large filters in the attic instead of the ones located at the return air grates.

some economizers would be a God sent with todays energy market. I am just not sure if it would be benificial on those small DX units. They just don't unload enough because most are a single circuit until you get up to 5 tons. I think these companies that sell residential units are going to have to start developing new systems that can perform a more controlled function. Especially for this area where it still gets pretty humid. Without being able to unload down to .5 or 1 ton, an economizer would be pretty worthless. I wonder if you could do that with a hot gas bypass though. Hell, maybe I have an idea for a new company. :o