Passive solar heater to dry out crawlspace?

I have a passive solar heater I made, it's been kicking out 160 degree heat on below freezing days all winter.  

The rental we are in has shown up with bad mold in the crawlspace, I'm very sick. Mold remediation guys did a better vapor barrier, installed a sump pump, and sprayed a bleachy type chemical. We left the crawlspace door off, and opened what vents it has (not adequate vents at all.)  I'm working on getting us out of here. In the meantime, I'm considering hooking my solar heater into the crawl space for the summer.

I THINK it would
A) add cross ventilation to the space
B) increase the heat, which would increase how much water the air can hold, which then
C) would cross ventilate out the excessively moist air, resulting in
D) a dryer crawlspace, less conducive to mold growth.

Am I correct in this thinking?

I realize it may heat the house more, oh well. I would rather pay the electric bill than the doctor bills I'm paying. I have to get healthy enough to cope with getting us into our own home.

Hi Miss Pearl;   You sure know how to get a Permies guys attention...  just post on a thread he's on!
In my humble opinion, I think all you need are fans. Blowing hot air from outside in and sucking it back out on the other. You may need to enlarge a vent hole on the off side to let in enough air.

As far as your solar heater, well why not. It sure won't hurt.
I'm thinking your about to start getting hot outside.  Your humidity will be rising to summer intolerable level's soon as well. With fans that might be enough.


Now on to your health!   Dang it stop that and get better!  Permies invests a lot, in us super staff type people! You can't be feeling down! We are all waiting on the next instalment of your house build!

I  seriously hope you are feeling better soon my friend , it makes me a little down knowing that your not feeling 100%!

Thank you Thomas  :) Glad you are pokeable :)

Fans are not an option, no power available, and they'd get rained on, they can't be put into the crawl space. Increasing the size of the vents is not an option, would take a jackhammer. I refuse to spend time doing structural work on this place, I'd rather put my time into getting us out of here. The vents in place are way too few, too small, and covered with grilles and screens that further restrict the air. I'd pull one of them off to run the solar into the crawl space. Not sure how much damage that removal will do, looks like cement nails going into the concrete wall. I'm willing to take a crowbar to one of them, but not to do the surgery it would take to remove them all, since they'd need animal-proofing etc, and would add to the cold floors in this house if they can't be covered again. Really not sure how much damage is going to be involved. I have the crawlspace cover off, with just hardware cloth over it, that would be my output vent.

So you think my logic about what the solar would do is correct? I'm brain fogged BAD from all this, not sure I'm thinking clearly at all. It is going to be hot and muggy soon, but it's  muggier in the crawl space. The solar pulls the air fairly hard due to the heat rise, well designed system with thermal mass and turbulence, so it would act somewhat like a fan, not just a passively sitting there heater.

Ok;  So go ahead and knock open one vent and plumb in the solar heater.  We will see how well it works.
You are correct , hot air does rise.  Could work just fine.
If needed you still could use a fan at the big hole , you'll just need to give it a plywood roof / walls.

thomas rubino wrote: Ok;  So go ahead and knock open one vent and plumb in the solar heater.  We will see how well it works.
You are correct , hot air does rise.  Could work just fine.

Cool, was checking for obvious bad idea :) The solar does put out quite a rowdy airflow.

If needed you still could use a fan at the big hole , you'll just need to give it a plywood roof / walls.

There's no power.

From https://en.wikipedia.org/wiki/Boric_acid

"In combination with its use as an insecticide, boric acid also prevents and destroys existing wet and dry rot in timbers. It can be used in combination with an ethylene glycol carrier to treat external wood against fungal and insect attack. It is possible to buy borate-impregnated rods for insertion into wood via drill holes where dampness and moisture is known to collect and sit. It is available in a gel form and injectable paste form for treating rot affected wood without the need to replace the timber. Concentrates of borate-based treatments can be used to prevent slime, mycelium, and algae growth, even in marine environments."

And " boric acid is only poisonous if taken internally or inhaled in large quantities."

yeah I mix roach powder into paint

Pearl Sutton wrote:
There's no power.

Hey... what about using solar for a fan? There are 12V DC fans from Desktop PCs (around 1$ each). You could hook them to a (used) 12V car battery. They should run for days on a battery load. But you could use a 20-30watt solar panel (nominal 12V, 25-40$) and a cheap 5AMP charge controller (7-15$).

Solar heater hooked to the crawlspace, could not remove the vents, the siding was redone a few years ago, and they covered half the vent with new plywood, and those are not removing without serious work, cement nails below the plywood, which is under the siding. I got the screen off one of them, cleaned up the bars as best I could, and hooked to it. Best I can do. This place is bad design mixed with bad construction.

High tech vent attachment system consisting of a couple #10 cans, metal tape, 2 bricks, and more dryer vent. I haven't checked it yet today, but I think if it does not do what I envisioned, it will be running backwards, so it will pull the air out of the crawl space and vent it out the input tube. That's still a win in my book. The solar might just add to the air flow and maybe heat kill some mold as it comes out.

Thank you all for help!!

Sloppy picture, two shots, slightly different angles, pasted together.

Congratulation's Mizz Sutton!  
You have completed the final test!
We are glad to tell you that you have received a    4.0 in hillbilly technology 1.0 . Please present yourself to the front desk to receive your bib overalls and corncob pipe.
If you wish to receive your muzzle loader you must first complete hillbilly technology 2.0.  Application's available online. Have a great day Pearl !  I'm hoping your up to at least 50% today!

thomas rubino wrote:Congratulation's Mizz Sutton!  
You have completed the final test!
We are glad to tell you that you have received a    4.0 in hillbilly technology 1.0 . Please present yourself to the front desk to receive your bib overalls and corncob pipe.

I have aprons and bare feet, does that count?
And I am a classic build something bizarre type. Have done that all my life. I think I qualified for the pipe etc long ago :)

If you wish to receive your muzzle loader you must first complete hillbilly technology 2.0.  Application's available online. Have a great day Pearl !  I'm hoping your up to at least 50% today!

oh hey, I'd like a muzzle loader! I bet if I don't have the credentials for the application, I can CLEP it. :D

Thinking on it, after I wrote the post, the input line is also dryer vent, if it runs backwards, due to chimney effect, I'll swap which pipe it's on. Still hope it pushes hot down, but a good pull works too. :D
Not at 50%. But going out to plant anyway. :D  Finally warmed up enough. I've been antsy for a month or more.

Pearl Sutton wrote:

Am I correct in this thinking?

I realize it may heat the house more, oh well. I would rather pay the electric bill than the doctor bills I'm paying. I have to get healthy enough to cope with getting us into our own home.

Your thinking is accurate, attached is  a moisture capacity versus temp for air. You'll notice you'd really have to heat the air to get a really big boost in moisture capacity difference.

Here's how I'dve hooked up the solar air heater to suck air out (notice it won't heat the crawlspace or you  though):

If you have more than 18" height difference between the north side crawlspace intake and the south side crawlspace outlet , you'll already have a convection flow velocity before you even get to your passive solar air heater.  
To take advantage of this small velocity,  put the solar air heater's base on  a stand such that the solar air heater's intake is level with the south side crawl space outlet

I'm also assuming you constructed your solar air heater such that the output as heigh as you could get it and your intake was as low as you could get it.

Arranged in this manner, you would get the highest air velocity out of your sah, bringing in the ambient coolest air (shaded north side of house) towards the hottest ambient air (south side of house).  

Good luck and hope you spend as much time away from that house as possible.

Pearl Sutton wrote:
Thinking on it, after I wrote the post, the input line is also dryer vent, if it runs backwards, due to chimney effect, I'll swap which pipe it's on. Still hope it pushes hot down, but a good pull works too.

What if you were to:
1) Seperate the two cans, put one of the "lids" back in place, hung by a single wire, top dead center. (Red arrow)
2) Install a horizontal wire through the can on the right, very close to the "lid" so that it can't swing in that direction. (Blue line) This could be done with a few screws instead.
3) Reassemble the cans.

If I'm right, (Hey, it could happen!) you'll have built yourself a hillbilly check valve. Since it wouldn't be airtight, air could flow slowly in the wrong direction, but any significant airflow toward the crawlspace would move the flap and be unhindered. Any significant airflow toward the heater would close the flap and meet resistance.

Do you think your heater pumps enough air for this to help?

Orin Raichart wrote:

If you have more than 18" height difference between the north side crawlspace intake and the south side crawlspace outlet , you'll already have a convection flow velocity before you even get to your passive solar air heater.  
To take advantage of this small velocity,  put the solar air heater's base on  a stand such that the solar air heater's intake is level with the south side crawl space outlet

Unfortunately, that assumes this place has any kind of rational venting, which it does not. I have the east side access hatch  (12 inches x 24 inches) open (that's WAY too small for an access hatch, I got hurt getting out of there)  and one vent on the south side (6 inches x 14 inches, with wide bar grille, so it gets only about 1/2 the airflow you'd expect) that I hooked the solar to.

I'm also assuming you constructed your solar air heater such that the output as high as you could get it and your intake was as low as you could get it.

The solar was an experiment in thermal mass and turbulence, hooked to this house the only way I could get it, which put both vents up top, to go through a window, and the intake goes down to the bottom before it gets into the sunny section. It was experimental, not meant to work really well, just to see what happened with the turbulence etc. (Took it up about 20 degrees!)  

Arranged in this manner, you would get the highest air velocity out of your sah, bringing in the ambient coolest air (shaded north side of house) towards the hottest ambient air (south side of house).  

Yeah, I'm thinking I'm going to move it to the intake vent, seems like most likely to be effective.

Good luck and hope you spend as much time away from that house as possible.

I'm doing my damnedest to get us out of here and into our house we will be building, one of the current problems being I got SO SICK I haven't been able to cope, and without me, it doesn't happen. Thanks for your good wishes. :D

T Melville wrote:

Pearl Sutton wrote:
Thinking on it, after I wrote the post, the input line is also dryer vent, if it runs backwards, due to chimney effect, I'll swap which pipe it's on. Still hope it pushes hot down, but a good pull works too.

What if you were to:
1) Seperate the two cans, put one of the "lids" back in place, hung by a single wire, top dead center. (Red arrow)
2) Install a horizontal wire through the can on the right, very close to the "lid" so that it can't swing in that direction. (Blue line) This could be done with a few screws instead.
3) Reassemble the cans.

If I'm right, (Hey, it could happen!) you'll have built yourself a hillbilly check valve. Since it wouldn't be airtight, air could flow slowly in the wrong direction, but any significant airflow toward the crawlspace would move the flap and be unhindered. Any significant airflow toward the heater would close the flap and meet resistance.

Do you think your heater pumps enough air for this to help?

I haven't checked it yet, at this point I'm thinking odds are high it will pull better than push, so I'll change it over.
Like I said above, I'm incredibly sick from this, and doing what I did kicked my ass hard and took way too long, taking it apart again is more effort than I can handle. Changing the ducting is easy, no crawling on rocks in the shrubbery.
I will save that idea for later, I am doing odd stuff with venting in our house! (Not this rental, I'm just getting us out of here.)

Burl Smith wrote:
yeah I mix roach powder into paint

I ran across the following on my travels here:

Terry Ruth wrote:

Rather than a plastic floor, try 70% bentonite clay, 25% magnesium oxide, 5% borax a thin milk like mix spray it onto all crawl space areas as a breathable water proofer;

https://permies.com/t/40/43637/Breathable-Walls

perhaps a note left for future tenants or the landlord might prove profitable for them.