HVAC supply FOR the attic?

[ScorpionLeather]

While working in my attic under all the temp extremes, the thought occurred to me - what if I put a manual damper or independent zone control to open a vent just for the attic space. Has anyone seen a setup like this or installed one? If I were to ever do this, I'd want a very tight sealing damper so that it's not losing any air into the attic when it's not in use. I'm putting insulation on the ducts right now and I'm just glad it's not the summer when it's cooking like an oven up there.

[George2]

I don't understand, why do you want to heat or cool your attic?

Are you going to make it a livable area?

[ScorpionLeather]

I don't understand, why do you want to heat or cool your attic?

Are you going to make it a livable area?

It will never be a livable area but I was thinking it would be easy to make a supply up there that could be opened on rare occasion while working in the attic on a hot summer day. The main downside I'm thinking it would be hard to insulate the supply even when it's sealed shut.

[JimmyM]

Years ago while repiping my house I removed a couple of the supply registers from the ceiling and just pushed the supply boxes up into the attic while I was working up there. Then I just put everything back when the job was finished. Worked great!

[Southern Mech]

If you cool your attic, in theory would make your house in general cooler, heat rises, a hot attic slows down the transfer of heat up and out of the envelope.

[Southern Mech]

much like an attic fan would act. without the convection it would all be radiant.

[beenthere]

Since there is no return in the attic, or return path from the attic. it would also put the house into a negative pressure. And draw outside air into the rest of the house.

[hvacrmedic]

If you cool your attic, in theory would make your house in general cooler, heat rises, a hot attic slows down the transfer of heat up and out of the envelope.

Nope, nope, and nope. Points to ponder:

Why would the house be cooler with a cooler attic. Does the t-stat sense attic temperature?

An infrared heater hangs from an automotive shop ceiling. Does the heat radiated from the heater rise? Poor guy changing tires says "Wtf boss, why aren't those heaters mounted on the floor, all that heat is rising right up through the roof and I'm freezing down here."

A hot attic sits above a less hot or cool space below. Which direction is the heat going to flow. Heat flows from warmer to cooler, right? The attic insluation slows the transfer of heat "down" into the conditioned space.

I know I'll probably catch some more flack, but hey, it's something to do, you should be glad that I'm giving you all something to argue piss and groan about :)

[hvacrmedic]

While working in my attic under all the temp extremes, the thought occurred to me - what if I put a manual damper or independent zone control to open a vent just for the attic space. Has anyone seen a setup like this or installed one? If I were to ever do this, I'd want a very tight sealing damper so that it's not losing any air into the attic when it's not in use. I'm putting insulation on the ducts right now and I'm just glad it's not the summer when it's cooking like an oven up there.

We do that (temporarily) on a lot of attic installs. Attic air will pull down into the house through the openings that you leave. If nobody's home it doesn't matter does it?

Go for it, it's your house, do what you want.

[BaldLoonie]

Probably won't make a dent in the temp other than putting your face in front of it now & then.

[SBKold]

Trust me Loonie is right.

You aint goona feel it unless you are working in one spot.

[genduct]

Since there is no return in the attic, or return path from the attic. it would also put the house into a negative pressure. And draw outside air into the rest of the house.
BEENTHERE has his finger on the problem! What you think you're saving is coming back in with increased infilltraion caused by the negative house pressure

[ScorpionLeather]

BEENTHERE has his finger on the problem! What you think you're saving is coming back in with increased infilltraion caused by the negative house pressure

I agree this would make no sense for regular use. My idea was to open the damper on rare occasion while working in the attic on a hot summer day. I can understand that a single vent would probably take forever to cool the attic unless I stick my face in it. But due to how easy it would be to modify the metal ducting to make this happen, why not, even if it makes a little difference. I remember just recently, the electrician kept telling me to bump the schedule to October rather than September because he doesn't like working in hot attics. Now the main reason I hesitate to add a supply vent to the attic would be due to the difficulty of insulating the opening portion and creating a tight seal with the damper and grill so that it doesn't leak any air when it is fully closed 99% of the time unless I'm working up there.

[genduct]

If you going to work in the attic, take one of those hoses with the holes to sprinkler the lawn and put it on the roof ridge to wet the roof. this will cool down the roof and lower the temp in the attic space
try to start at 6 and have it done by noon

[luskys a/c]

Do you have a ridge vent on your roof or some roof vents? You should just have a couple wall fans w/ shutters installed because like the others said , once the temp/humidity gets above avg. your a/c will not do what you want it to do and bring down the temp enough to keep the sweat from rolling off your nose.

[Southern Mech]

Nope, nope, and nope. Points to ponder:

Why would the house be cooler with a cooler attic. Does the t-stat sense attic temperature?

An infrared heater hangs from an automotive shop ceiling. Does the heat radiated from the heater rise? Poor guy changing tires says "Wtf boss, why aren't those heaters mounted on the floor, all that heat is rising right up through the roof and I'm freezing down here."

A hot attic sits above a less hot or cool space below. Which direction is the heat going to flow. Heat flows from warmer to cooler, right? The attic insluation slows the transfer of heat "down" into the conditioned space.

I know I'll probably catch some more flack, but hey, it's something to do, you should be glad that I'm giving you all something to argue piss and groan about :)


You may want to seriously look into what I said, A cooler attic will most indeed help the envelope of the house. Fact. Now the radiant/convection crap Isaid maybe out in left field but the cool attic is not.

If hot air moves to cooler air, the hot ain in the envelope is say 80 and the attic is 140 well it wont move very fast will it, vs if it were 80 also the heat build up would escape from the hose at much more rapid pace.


Now if the thread OP is just wanting to do this while working up there he is basicaly pissing in the wind.

[hvacrmedic]

You may want to seriously look into what I said, A cooler attic will most indeed help the envelope of the house. Fact. Now the radiant/convection crap Isaid maybe out in left field but the cool attic is not.

If hot air moves to cooler air, the hot ain in the envelope is say 80 and the attic is 140 well it wont move very fast will it, vs if it were 80 also the heat build up would escape from the hose at much more rapid pace.


Now if the thread OP is just wanting to do this while working up there he is basicaly pissing in the wind.

Wow. I don't even know how to approach that. I'd be more than happy to provide a few lessons in thermodynamics, but since you already think you're smarter (and better) than than me, based upon your response to me in the other thread, it would probably be a wasted effort. If you can get past that barrier, then here's your first lesson.

If the air in the attic space is hotter than the air in the conditioned space below it, then any heat transfer between the two volumes of air is going to be in a downward direction. Heat from the attic will flow down through the insulation, through the ceiling, and from there will be transfered to the living space, acting to raise the indoor space temperature.

I think what you meant with your comment about the cooler attic is that a cooler attic will reduce the heat load on the air conditioner. That's correct in most cases, but not when the air conditioner is doing the cooling of the attic. I thought cooling the attic with the air conditioner is what we were discussing in this thread. If that isn't what you had in mind, then you'll need to be more specific.

[Southern Mech]

Wow. I don't even know how to approach that. I'd be more than happy to provide a few lessons in thermodynamics, but since you already think you're smarter (and better) than than me, based upon your response to me in the other thread, it would probably be a wasted effort. If you can get past that barrier, then here's your first lesson.

If the air in the attic space is hotter than the air in the conditioned space below it, then any heat transfer between the two volumes of air is going to be in a downward direction. Heat from the attic will flow down through the insulation, through the ceiling, and from there will be transfered to the living space, acting to raise the indoor space temperature.

I think what you meant with your comment about the cooler attic is that a cooler attic will reduce the heat load on the air conditioner. That's correct in most cases, but not when the air conditioner is doing the cooling of the attic. I thought cooling the attic with the air conditioner is what we were discussing in this thread. If that isn't what you had in mind, then you'll need to be more specific.

alway's wanting to learn, I am lacking in the scientifics for sure.

I do understand the attic load on A/C in second paragraph.

I don't uderstand is how how heat fall's, being I was alway's taught heat rises and cold air fall's?

And as far as what I said in another thread,sorry if I offended you in any way. Sometime's people don't see eye to eye through typing.

[ScorpionLeather]

I don't uderstand is how how heat fall's, being I was alway's taught heat rises and cold air fall's?

Although hot air rises and cool air falls, a more general physical phenomenon applies considering the total average temperature of a space and how this affects another space.

For the general case, it works according to the 2nd law of thermodynamics. Without an input of external energy, heat flows in the direction of hot to cold and not the other way around:

http://theory.uwinnipeg.ca/mod_tech/node79.html

But the explanation doesn't have to get scientific.. it is even simpler.. it would be inefficient to cool the attic for the purpose of keeping the house cool because in most cases attics are poorly insulated from the roof and many are vented to the outside. So the duct going to cool the attic would waste a lot of the cooling energy which escapes outside. The attic would be colder of course reducing the heat transfer to the living space below (2nd law of thermodynamics) but this cooling energy would be more efficiently applied to the insulated living space.

By the way I liked the tips on wetting the roof with a hose and working in the attic early in the morning. This reminds me of the tips my pool builder friend gave me.. he gets up super early (before the sun comes up) in the hot summer and he puts a wet towel over his head while building pools. Those things are like parabolic reflectors and can cook you just like a hot attic. I fixed up my pool last summer, speaking from experience!

[westval]

It will never be a livable area but I was thinking it would be easy to make a supply up there that could be opened on rare occasion while working in the attic on a hot summer day. The main downside I'm thinking it would be hard to insulate the supply even when it's sealed shut.

Say you open this vent on a cooler day. Now you are pushing supply air to the attic that has no return to the house. Your supply moves, lets say 1600 CFM. That means your return must also move 1600 CFM. If you move 200 CFM into the attic you are now moving 1400 into the house but trying to suck in 1600. That 200 will come from somewhere. Maybe the attic, a leaking window, or under a door. Or it may come from the garage where you just started a car, snowblower, or opened a can of paint thinner. Now you have just induced 200 CFM of poison into your home. Houses in negative pressure will kill you. CO has no prejudice. It is an equal oppertunity killer.

[hvacrmedic]

Although hot air rises and cool air falls, a more general physical phenomenon applies considering the total average temperature of a space and how this affects another space.

For the general case, it works according to the 2nd law of thermodynamics. Without an input of external energy, heat flows in the direction of hot to cold and not the other way around:

http://theory.uwinnipeg.ca/mod_tech/node79.html

But the explanation doesn't have to get scientific.. it is even simpler.. it would be inefficient to cool the attic for the purpose of keeping the house cool because in most cases attics are poorly insulated from the roof and many are vented to the outside. So the duct going to cool the attic would waste a lot of the cooling energy which escapes outside. The attic would be colder of course reducing the heat transfer to the living space below (2nd law of thermodynamics) but this cooling energy would be more efficiently applied to the insulated living space.

By the way I liked the tips on wetting the roof with a hose and working in the attic early in the morning. This reminds me of the tips my pool builder friend gave me.. he gets up super early (before the sun comes up) in the hot summer and he puts a wet towel over his head while building pools. Those things are like parabolic reflectors and can cook you just like a hot attic. I fixed up my pool last summer, speaking from experience!

Good answer! Have you applied for pro membership yet?