Stupid idea? Using attic heat?

doc henderson · September 10, 2020, 12:52:32 PM

could also put it on the roof and use insulated duct work through the roof and attic space. just tell your better half that Doc Henderson said so! i am sure that will work! :D :D :D

ps I take making your head hurt as somewhat of a compliment! ;)

mudfarmer · September 10, 2020, 02:12:06 PM

You said you don't want processors and other sorts of junk and I am right there with you but you can get differential temperature controllers for <$50 online with two temp probes that can handle ranges of below freezing to above boiling.

They are basically a relay triggered when the difference between the two probes is what you set it to. Some of them have two relays and two setpoints. You could use this to run your fan when t1-t2 > (some amount you decide on) and the second relay to run a solenoid/actuator to close off the duct like doc mentioned when attic temp is lower than shop temp to keep your heated shop air from rising back up through your pipe?

Just spitballin'

mike_belben · September 10, 2020, 02:53:49 PM

Hot only travels to cold.

Insulation only slows the rate of heat travelling to cold, whether the heat is inside [winter] or outside [summer.] Insulation does not prevent a temperature rise or fall. Only delays one.

A cardboard house gets hot 3 minutes after the sun hits. A regular house 3 hours, a subsurface concrete mountain bunker maybe 3 weeks. Mass of materials also comes into play and it can be hard to tell whether it is insulation or mass creating the lag in thermal change. Id say both.

An uninsulated, vented attic will be hot by noon. Insulated one maybe 7pm.

I see this as a discussion about relocating unintended heat to an intended location. Not about slowing the rate of heat transfer.

Ianab · September 10, 2020, 03:58:54 PM

Quote from: mudfarmer on September 10, 2020, 02:12:06 PMYou said you don't want processors and other sorts of junk and I am right there with you but you can get differential temperature controllers for <$50 online with two temp probes that can handle ranges of below freezing to above boiling.

That was my thought too. What you want is a fan that runs when the attic temp is higher than the room below. During a sunny day it will be, so you want the fan to turn on once it's warm enough up there to do some good. Early morning / night you don't want that, leave the cold air upstairs. A simple differential controller would be enough to handle things, although you could get more clever if you wanted.

You can probably shutter off the attic vents because you are going to be recirculating the air with the fan system. You could fit an interior vent that takes cool air from ground level back up into the attic when the system is running.

Something like an extractor fan with powered louvres should be ideal as it will seal the vent when the attic space is cooler than the room, preventing warm air from leaking back into the attic.

Commercial systems like this are commonly available for homes here in NZ, but the main advantage is ventilating the house with warm dry air to reduce condensation inside. (a big problem in a humid climate) They have the benefit of helping to warm the house as well, but they don't do any good when it's most needed (cold nights).

Old Greenhorn · September 10, 2020, 04:03:44 PM

Yes, Mike, Crusarius, Mud Farmer, Southside, Don, {edit to add} Ianab, and Doc. Starting simple, steal the wasted heat in the attic, if there is any to be got. If the return proves worthwhile I plan to go pretty much exactly as Mud Farmer suggests. In the beginning I will just crack a window to allow air to move out. I won't need much, there is already leakage around the two garage doors and human doors. If the test works, I will look into floating air from the floor level in the shop (coolest air) back up into the attic and then pumping it down from the attic at near the peak level (hottest) down into the shop. All controlled by a differential switch of 'some sort'. I would only expand on that in the event that the ROI in time and cost would prove worthwhile. I am a simple guy. Doc knows my buttons and he is baiting me into a more 'robust' project, knowing full well that I will be thinking about the seeds he planted as I go forward and may 'alter my goal' so he can see what develops. ;D I am a BIG fan of simple experiments and steps to prove the concept, THEN going in full tilt when the rewards are justified. I am not a big fan of thinking about it too much and trying to figure out EXACTLY how it will 'end'.
I won't even do any more than think about this until I have the chimney installed and the wood stove warming my coffee. Of course, I will start collecting data as soon as the gadget arrives.

doc henderson · September 10, 2020, 05:05:09 PM

cool! oh sorry, I mean "warmmmm"! no buttons were pushed intentionally in the making of this movie!

Old Greenhorn · September 10, 2020, 05:45:34 PM

Ah, push away, it make me think. :D

Al_Smith · September 11, 2020, 10:19:50 AM

This might sound silly but I saw it .A gent I know set up a series of PVC pipe in his attic to capture the passive heat of the spring time sun to heat his in ground swimming pool .It worked .

Hilltop366 · September 11, 2020, 10:27:04 AM

For the no electronics approach?

Wondering if one could use a mechanical line voltage cooling thermostat (in the attic space) to switch on/off circulating duct fan when the temp reaches a set levels then add a normally closed motorized dampers in the inlet and in the outlet ducts also controlled by the thermostat powering the 24v step down transformer.

For the attic vents a low voltage (24v) cooling thermostat to monitor the roof surface temp (mounted to the underside of roof deck to close normally open attic vent dampers once there is potential to heat the attic enough to provide supplemental space heating.

So in the end it would work like this:

Sun shines on roof.

When underside of roof deck reaches preset temp the 24v mechanical thermostat turns on and closes attic vent dampers.

Attic heats up.

When the preset attic temp is reached the 110v thermostat turns on the circulating fan and powers the 110-24v step-down transformer to open the duct dampers.

Sun on roof lost. (clouds, sunset)

Roof surface temp drops below preset temp the 24v mechanical thermostat turns off and opens attic vent dampers.

doc henderson · September 11, 2020, 06:49:48 PM

had a buddy with with a length of garden hose back and forth on the roof, and water to fill the pool went through all that black hose during the day. could put a circulation pump on it as well. in college we had a big kiddie pool. when it was cold, we put a galvanized metal container on top of the Weber grill. use the little filter pump to pump the pool water up to the container, and siphoned the hotter water back into the pool.. was fun and made a temp difference. say 10 degrees in 2 hours. pool was 18 inches deep and 10 foot around. the container bottom was about the size of the Weber grill and 12 inches tall.

Al_Smith · September 11, 2020, 07:02:41 PM

My once time brother in law used a section of perforated garden hose and let it dribble down the south facing side of garage roof of black roofing .Let it get into the eave spout and into the 4 feet deep 16 foot round pool .It used a small pump to recirculate the water and ran it through a multi screen filter to keep the gunk out of the water .It worked pretty good .

Old Greenhorn · September 11, 2020, 07:35:15 PM

Well I don't have a pool, so no worries there. I am putting this 'thing' on hold until I get the chimney and woodstove done (more of that in another thread), but I did another 5 minutes of piddling with this today while waiting for Fedex.
My neighbor who is moving away, gave me a crawl space vent fan he had bought but never needed to install. I thought I would stick that up in the attic opening just for giggles. Turns out this fan is controlled by a humidistat. Not the best for this experiment, but it will do for now. Yes, it does move the heat down. It was cool in the shop today and mostly cloudy but the attic was pretty warm. It did move some air down. It shows promise.
I will probably start messing with this in 2 weeks or so. For now, I am all about chimneys.

mike_belben · September 11, 2020, 07:59:28 PM

My water heater cold inlet line wound through 30 feet or so of soft copper in a big insulated lobster pot on the cooktop wood stove. And i built a thermal siphon coil next to it too.

We had some dang hot showers.

Friend of mine in CT has a water loop in his garage woodstove plumbed to a jeep radiator and electric fan in his upstairs apartment pretty far away. Heats the living room.

Gary_C · September 12, 2020, 04:13:04 AM

What you are trying to do is capture the energy from the sun that strikes the roof and move it to another location. It can be done but not the way you guys are approaching the idea.

First air has very little mass or weight so it has little energy holding capacity. Trying to move energy using air is difficult as it requires large ducts and lots of insulation to keep the little bit of energy air holds. Water is a far better energy transfer medium.

Second using a roof as a heat transfer material is not going to work. Yes in high ambient temperatures the roof will get hotter than ambient but that is not the time when you are needing a temperature boost. In low ambient temperatures the roof will not get warm enough to help in boosting indoor temps. The ideal roof in low ambient temps will not melt snow so it will not be of any use in indoor warming. Yes if you could collect the energy for some time it would be useful but an uninsulated roof is not going to be much above ambient outside temps and you will need air or water temps that is above indoor temps.

So how can it be done as I said earlier? Build a large enough solar collector that is insulated and where you let the sun's energy inside to heat water in black painted pipes so that you heat the water well above the temperature you need to add heat to the shop. Or use south facing windows to directly heat large thermal masses that are dark colored. Simple enough right?

Old Greenhorn · September 12, 2020, 05:01:37 AM

Quote from: Gary_C on September 12, 2020, 04:13:04 AMSimple enough right?

I say this with all due respect Gary: No, it's not simple enough. ;D You have no idea how simple my mind works. :D
Back in the original post I said I just wanted to grab the air air from the attic and move it into the working space of the shop to Add a little heat, not heat the entire shop 24/7. I don't think it is complicated to move heated air about 50" from the Attic into the working space. When I get around to this I will just stick with the basic plan and controls that are discussed in the previous posts. It just comes to a point of ROI and putting all that effort into fancy stuff to have a fancy system is not worth it for me. BTW, my roof is not insulated, the attic floor is insulated, so the attic gets DanG hot when the sun is on it, even on cool days. There is about 1,200 sq.ft. of roof collecting that heat, so I think it is pretty easy to try and grab some of it and use it.
Anything more complicated than what we are planning would not be worth the effort when I can just split another half cord of wood to make up the difference.
BTW Doc, that kiln idea sounds like it might be a winner. Some of those pine boards I threw up there are drying like crazy already in just a couple of days. I'll have to stick the meter on them to see what I have.

Old Greenhorn · September 12, 2020, 06:31:37 PM

Not that I am working on this now until I get the chimney and stove done, BUT I did note that the ambient temp barely broke 70 today, it was 60-65 in the shop and over 90 in the attic. This is going to work. Man, working up there is no fun. ;D

mudfarmer · September 12, 2020, 10:51:52 PM

Mike mentioned thermosiphon.. We had a stainless tank (open to atmosphere) at ceiling height heated by copper coil around stovepipe, gravity fed to bottom of coil. Heated water rises back to tank. Worked great for hot water. It would even boil in the coil and you could hear it shooting back into tank (boiler explosions are no joke and super dangerous that is why tank was open to atmosphere). Also use a copper tube preheater for our maple syrup evaporator. Lot easier to heat sap from 100*F to boiling than from 32F. That is backwards for OGH purposes, heat down not up and I am rambling.

Look up "snap disks" (discs?) online. Basically a bimetallic thermostat/switch that does a thing when it gets to a certain temp. Few dollars a piece a decade ago. Maybe epoxy to underside of roof. I want you to succeed and know you can! Don't let perfect be the enemy of good enough

Editing post, we had an apartment one time where I built a solar air heater using 2x6s, aluminum dryer duct, PC case fans, foam insulation and old free storm windows from side of road. Built a faux window A/C basically to close in the window w input and output ducts. That is where the snap disk thing came from.

Ljohnsaw · September 12, 2020, 11:51:43 PM

Quote from: mudfarmer on September 12, 2020, 10:51:52 PMLook up "snap disks" (discs?) online. Basically a bimetallic thermostat/switch that does a thing when it gets to a certain temp. Few dollars a piece a decade ago.

I made a solar air heater a couple of years back as an experiment. I got a piece of twin layer Lexan from a plastic supply place. I ordered an 8' piece but they gave me a 10' section. I didn't realize until I went to put it into my truck bed that is was longer. Anyhow, I got two sheets of 2" foam insulation and used aluminum foil tape to assemble. I used some rain gutter to make a plate absorber that I painted black. I used two inline duct fans with some 4" aluminum dryer hose. I made a manifold on the far end to turn the air around to the other gutter. I installed a snap switch that clicks on around 85* to fire up the fans. I got a few different ones for a buck or two each and found one that was right for this setup. Works pretty well.

Old Greenhorn · September 13, 2020, 06:47:01 AM

Not that I am working on this, because I am not, but I had some time at around 4 this morning and did a little poking around. I found a solid state controller on eBay for under ten bucks that looks like it will do the job. I don't like the probe wire lengths available (3' max) but I will have to work with it. The built in relay will handle 20A, so good on that score.
HD has a 10" duct fan for just over 50 bucks, so that with a short piece of pipe (3'?) and some kind of grill/shutter and I will have the beginnings of an experiment. Gonna leave the shutter control off for now or maybe just go manual. This is an entry level, proof of concept test at this point so I can learn more. I will have to see how much heat I can pull and how long it holds up when I start dragging fresh air in the attic. I might need 2 of these setups, or I might need to close off the gable vents and use makeup air from the shop to re-circulate. Time will tell.
I haven't ordered anything yet because it all looks like short lead time stuff. I have gotten by without this for a long time, I can wait a few more weeks and call it a fall project.

Don P · September 13, 2020, 07:36:57 AM

Block the fresh air, you only need to move the warm air to the shop and replace it with cooler air from the shop. The fresh air is to remove moisture. Monitor the humidity and if needed bring in fresh air to solve that, a humidistat can control the fresh air vent if needed. I doubt it will be needed, you'll probably get that exchange from shop leakage.

mike_belben · September 13, 2020, 08:27:25 AM

What don said. The shop space has your cool makeup air. You just need to shove the hot stuff down. It will pressurize the lower level which will force itself upward to achieve equilibrium.

The downspout tube i guess we could call it, needs to be distant enough from the upspout (probably the attic access hatch) that the dont short cycle. If you blow the heated air right into the jetstream of the rising cool air itll just do a yoo-ee and head back up.

I expect youll need to cut atleast 1 ceiling hole for the final version. And it would be well to run a round tin duct down to a tee thats laying upside down on the floor, -almost like a gutter with left and right discharge- so that the warm air can blanket the coldest wall, away from the wood stove. If youve got say 2 overhead doors, theyre leaking in cool air at the seals. Id put that heat gutter right between the two for instance.

The further this heated air has to travel to get back upstairs, the more of it youll get to use.

Tacotodd · September 14, 2020, 05:05:58 PM

OGH, have you considered scrapping the hot attic air in place of something like a geothermal setup? The reason that I ask is that I proposed a OWB for my house to one of my friends and his response was that geothermal was much more financially viable after the first year and was practically free every day after. He also said that he was part of an installation crew and the cost for the labor of this crew was negligible. I don't know how set you are on your attic heat idea, but you know, sometimes outside ideas are the bees knees!

Just a thought. TA

Old Greenhorn · September 14, 2020, 06:34:48 PM

Well Todd, the short answer is...NO. :D I am looking for simple and cheap. Reply number 39 above pretty much covers it. I don't have the time, money, or inclination to get carried away. Just trying to make use of something already sitting there going to waste.
The temp/humidity gauge arrived today so I stuck the probes in the attic and went back to work. I checked it a few times, but it was a cool day and hardly got up to 70 and was overcast all day. The attic temp was 83 and as the temp went up, the humidity up there went down. I will keep an eye on it for a while to decide how I will proceed.

doc henderson · September 14, 2020, 07:17:47 PM

surely the rest of us can dream and try to spend your time and money!!

have fun. you are putting the rest of us to shame. my only saving grace is I still work!

Old Greenhorn · September 14, 2020, 07:44:11 PM

OH surely y'all can conjure up anything you like, just don't give me more work to do. :D I have to stay at least a little bit focused. Going into the summer I was going to work on building some stuff to sell, that didn't really happen, and I wanted to get a bunch of lumber milled and that sort of happened, but mostly I got consumed by infrastructure improvements and things I knew had to be done. Firewood took a lot more time than I thought. So this one I am keeping simple if I do it at all. Lets see what the numbers show.