Using attic heat for the house
 

A couple of days ago, I stuck a thermometer up in my attic. Nothing fancy, just a wired unit that shows temperature. As its getting cooler, I'm finding the house cooling off slowly. I'd love to be able to get a bit more heat without having to turn on the furnace. So, last night I came home to find my attic at 92F (33C) at around 5pm and decided I was going to use some of that heat. I stuck a box fan into the attic access door and blew it down. Here is the very simple and quick setup.

http://ecorenovator.org/pictures/house381.JPG



Now, I'm not sure how much heat I really got out of it. The immediate area was definitely warm, but the room you see in the picture has a thermometer in the far corner and that didn't register any heat gain. However, when I went to sleep roughly 3.5 hours later the attic was still pretty warm as shown below.

http://ecorenovator.org/pictures/house382.JPG




So, it looks like the heat definitely has to be better distributed. I need a way to get it down to the first floor first. My first idea is to use the cutoff chimney in the attic! Its currently uncapped and probably making me loose a fair amount of heat in winter. I just haven't gotten around to putting some insulation around it yet.

http://ecorenovator.org/forum/attach...n-house385.jpg



To get it down to the first floor, I was thinking of using this vent hole that I had previously plugged up with foam. Its in my kitchen which is normally the coldest room in my house. Having some extra heat in there would be great.

http://ecorenovator.org/pictures/house189.jpg



So, I'm just kind of throwing out the idea to see what people think and get some suggestions. To get much heat I'd probably need a fair size blower/fan I'd imagine. I'm also not sure how long this will be useful? Will it be completely useless in winter? I guess we'll just have to see.

I also did a quick search on builditsolar and found this:
Attic based solar heting
attic temp logged data

These show that its not an original idea by far, and the temperature log of the attic I guess suggests that winter use really doesn't seem very viable. However, different climates and different types of construction will alter temperatures. So, I guess I'll wait and see.

That second link is very informative. It looks like the attic stays hot roughly from noon to 4pm, but it doesn't look like usable heat when it's really cold out. If you're only getting 4hr a day, three months out of the year, it's probably not great.

The attic would be a good location for the clothes dryer, though, assuming you do laundry from noon to 4pm.

what about installing a heat pump? the attic should always be warmer then the outside temp.

I would want some type of filtration on any attic air that I sent into the house. Too many bugs around here. And you don't want any insulation (especially if it's fiberglass) drawn into the house.

Wow, that attic looks strikingly similar to my except I've brought the chimney down to just below the floor level of the attic. If your chimney is as full of creosote as my was, I highly recommend against blowing any air down it. And definite seal any openings if you decide to remove anymore of it - the creosote and cement dust will create an enormous mess.

The first time I came across using attic heat was in John Seymour's book Blueprint for a Green Planet. Page 153 has a drawing of a solar house with a heat recycling pump, with the following description "This pumps the warm air that gathers in the upper parts of the house back to ground level where it is most useful".

If you have an unused chimney then go ahead and use it! It will save you the hassle and expense of running a duct between floors. Maybe make a circuit that checks temperatures and turns the fan on only when the attic is warmer than the kitchen? And Patrick is right about filtering.

Any chance of getting some insulation on that attic door?

Nah, the inside of the chimney is pretty clean actually, just a lot of cob-webs atm.

The attic got a good amount of cellulose blown in a while back, dust isn't too big and issue I don't think. If it is I'm sure I could filter it easily enough.

Thanks for the link skyl4rk. I just wonder how much heat there will be up there in winter. Robertsmalls says 4hrs a day which IMO seems like a healthy amount of otherwise free heat. Its hard to tell by those graphs though.

A heat pump wouldn't be a bad idea, but again I don't know how warm it'll be. All I have is the logged data from the first post. If the time window to pull heat is very small its probably not worth the work of trying to set one up.

Anyone got any info on an inexpensive data logger? I could use an arduino to make my own, but I don't have time right now for another project unfortunately. Most of the ones I've seen are very expensive for more than one channel logging ($100+).

Well, the house is still cooling off and I'm trying to hold back from turning the heat on. Tonight I came home from work to see the attic again at 90+ degrees F. So, I figured I'd give it another shot with an improvement. I found a piece of insulation to block the other part of the opening, so it should pull much more warm down. It does appear to be working quite a bit better now.

http://ecorenovator.org/forum/attach...1&d=1284761223

Its been roughly an hour now. I checked the temperature in the room and it has risen a bit over 2 degrees. :)

I only had about another 45 minutes before I had to leave last night. So, in just under 2 hours of blowing the attic air down, it brought the temp up from 68.5 to around 71.5. Not too shabby if I do say so. Well worth looking into IF the temperature gets high enough in winter.

I did this again last night. I wasn't very sunny yesterday, but the attic was still 72 and the upstairs was 66. So, I wanted to see what a 6 degree difference would do to me. ~2 hrs later the upstairs was 67.5 and attic was ~70. With so little temperature differential I didn't think there was much benefit, but I was happy to see the temp go up 1.5 degrees.

So, going forward I'm thinking of improving the setup. I think the next easy step would be to move the fan into the attic and set it on top of the cutoff chimney. I recently bought a remote outlet control for another project, but I'm thinking it would be perfect here for manual control. When I notice its warm up there, I flick it on and have warm air blowing down into my kitchen. Of course I'll need to unblock the previously blocked hole.

Ideas, thoughts?

Is there an all-season attic-vent-fan product on the market with bi-directional fans,
that's insulated, with a flap that shuts during winter nights.?.

It would be nice to clear out indoor hot air in the summer and suck down warm air on days like this..

Sorry, I haven't responded to a bunch of posts here.

That would probably work very nicely, but I'd like to start out as simple as possible for now.


Yeah, thats what I think I'm going to do. No filter for now. Its pretty clean up there so we'll wait to see if its a problem.

There is insulation above the door when its all closed up.

That is a great idea! I need to plug the chimney up anyways as I'm sure its a source of heat loss in the winter.

Anyone have any ideas on what products could be used like this? I'd imagine a bi-directional flapper door wouldn't be the easiest thing to come by.

It's 70 outdoors, 72 in my PC room right now (good solar), 66 in the basement and about 89 in the attic.

I have the pull-down door open about 8", so it doesn't get real hot up there..
Mainly, I want fresh dry air circulating in the basement. (for now).

When that pull-down door is sealed in the winter, it gets pretty warm up there..
Sun hitting any part of the roof will help keep the snow melting.. From the peak down.


I think my summer setup is okay, but I'll have to see if I can use some of that
attic heat for winter space heating.

Use an arduino or other microprocessor: When the attic is greater than 72 degrees and the house is less than 70 degrees, turn the fan on.

Yeah, thats probably the way I'll go eventually if all the manual testing works out.

So, I checked my chimney the other day. The opening is actually about half the size of my box fan. So, I'm thinking it would be a good idea to find some other fan for it. So, I'd imagine a squirrel cage fan would probably work better for this application since they're normally used for hvac stuff. I'm guessing because of their ability to create a higher pressure differential? Does anyone have any suggestions?

If you're going to use a squirrel cage fan, you can run it down the chimney since the discharge area is typically a lot smaller than a box fan. And it does produce a higher pressure differential than an axial fan.

Run it down the chimney? I'm not sure what you mean.

I originally planned to just set the box fan on top of the chimney blowing down. The problem is that the chimney is much smaller than the box fan. So, I need a smaller fan. Since I need a different fan I figured I'd switch to one that would work better as well (squirrel cage, thx for confirming my suspicion).

It might too high velocity for this application, but if you've got a leaf blower you could try setting it up with the discharge down the chimney.

Set the blower up in the attic so that the discharge blows down the chimney.

Thats a good idea. I was thinking a car blower would probably work decent. Possibly a furnace blower, but run at a lower speed. Can you simply disconnect 1 leg of the 110V an an AC motor?

Are you going to give the air an explicit return path as well?

If you use a car blower you can power it with PV panels. :D

I don't know about disconnecting one leg of 220. I think they make similar motors in 120V, though.

Here's a 120V motor that you might be able to make work: https://www.surpluscenter.com/item.a...tname=electric

Here are 2 complete blowers: https://www.surpluscenter.com/item.a...tname=electric

https://www.surpluscenter.com/item.a...tname=electric

Here's a cheap one if you don't want to invest a lot of money for a test: https://www.surpluscenter.com/item.a...tname=electric

Thats a good idea. I have thought of it but currently am not planning on using one. Unfortunately, the house is fairly leaky so there is no lack of places for the air to leak out of the house.

Wow thats absurdly cheap. I couldn't even find used car/furnace ones that cheap on ebay or craigslist.

I guess this brings up the question of how much flow should I try to shove through a 6" duct.

According to this site: Equivalent HVAC Duct Sizes By CFM, it looks like my 6" duct can flow 300 cfm.

I think my father in law has an old furnace blower laying around. I think I'll just ask him if he wants it anymore.

Anyone know of a way to slow down a 110V AC motor easily?

If you push 300 cfm through a 6" duct you'll have a 17 mph breeze coming out of it (appx).

Woooo lol :D Will mix up the air in the kitchen nice and good.

Try using a simple light dimmer. Most of them can do 600 watts..
http://www.homedepot.ca/wcsstore/Hom...5b8b3469_4.jpg

I'm currently at my in-laws house. My father in law is a master electrician and I knew he'd have something laying around. He just handed me two bathroom vent fans. These should do the job nicely. I'll get pics when I get home. They're about 6" in diameter and the one I'm lookin at now pulls .9A.

Cool! I mean Warm! :D You could rig it up with a thermostat (maybe from an attic fan) in the attic and another thermostat (for a heatpump or a furnace) in series in the kitchen so that the fan only comes on when the attic is hot and the kitchen is cool.

Yeah, thats what I was thinking. I'll have to dig through the differential temperature controller thread we had a while back. I was looking into making one. Perhaps now is the time, or maybe its time for me to buy a cheap kit and make one for a few bucks.

http://ecorenovator.org/forum/projec...ontroller.html

Farm Innovators Thermo Cube Thermostatically Controlled Outlet
has a model that comes on at 120F and goes off at 100F..

http://ecx.images-amazon.com/images/I/31KgRSZXw5L.jpg

I've been thinking of getting one of these for my attic fan.
It's old and it's sensor bit the dust many moons ago.

For now I might just keep it on manual control. Still working through the details. I'm definitely going to need some flapper door to stop cold air from shooting down the chimney.