Heating crawl space idea

[boisblancboy]

So I am heating my house with a Lopi Liberty which works wonderful, but I want to get my crawl space about 10 degrees warmer or so. Here is an idea I have and wanted to run it by all of you to get some feedback. This stove has the option of running a blower on it, which would pull air in from the bottom front of the stove and blow it out the top from. Could I hook some duct work where the blower would attach and run that down into my crawl space to a fan/blower, also close off the front/intake and have the fan pull air from the top front and down into the crawl space. I would have to have a return air from the crawl space back to the house to get circulation. Any thoughts on this? Suggestions?

Brandon

 

[LLigetfa]

First off, to exchange air between the living space and the crawlspace, the crawlspace must be deeemed "conditioned space" by code. That could be a show stopper. If not conditioned space, you could run a long duct through the crawlspace and back up into the living space so that it does not exchange air between the two.

My 4 foot crawlspace is conditioned space. It is essentially a drywalled basement with extremely limited headroom. I have a 650 CFM blower that takes cold air from the concrete floor, filters it, and blows it up through the bottom of my stove. Make-up air is drawn down into the crawlspace at a distance from the stove. The air warms the floor above from underneath and as it cools, it stratifies and gets picked up again by the blower.

 

[boisblancboy]

Yes I have a conditioned crawl space. 5 block high, 2.5 inches of foam board on the walls and a 2" concrete floor.

 

[jdinspector]

The foam board may be a showstopper. Usually, foam must be covered with non- combustibles, as it can give off toxic gases if burned. I understand that you consider it to be a conditioned space, but does the AHJ? ( authority having jurisdiction)

 

[boisblancboy]

Ok, its to code! I am a licensed builder who built the house and it was inspected as is. So please back to the question of actually getting heat down there.

 

[LLigetfa]

Well... I gave you two suggestions. You can move cooler air to the stove through the crawlspace and warmer air will take its place. Kills two birds with one stone. Takes the cooler air out of the living space and yet warms the crawlspace.

I have 2x6 PTWF with glass batts between the studs and rigid foam on the exterior.

 

[boisblancboy]

Do you notice much difference since you started heating the crawl?

 

[LLigetfa]

Do you notice much difference since you started heating the crawl?

I was both architect and GC so designed it that way from day one so there was never a before and after comparison.

 

[LLigetfa]

Insulation, be it Styrofoam or any other, is only one condition of habitable space head room being another and there is quite a definition of conditioned space
is a space through which air from directly conditioned spaces is transferred at a rate exceeding 3 air changes per hour it also has to have so many lumens too
means must be taken to eliminate mold mitigation too

Please lets not digress this into a code debate. The OP is a contractor and so should be aware of code issues just as I was aware of code issued and we both passed inspection. My gas furnace has 3 take-offs to heat the crawlspace if/when the woodstove is not heating it.

 

[jdinspector]

Sounds like it would help a lot. I've been in many homes that were cold because of a cold crawl. In fact, a friend of mine has a house in your neck of the woods (suttons bay, MI) that has that issue. He only spends a week per winter there, so isn't inclined to do something about it.

I see MANY homes with cold bedrooms that stick out over unseated garages- a classic problem. I think your idea will work to warm the crawl.

Out of curiosity, is your floor cold? Is that why you want to heat the crawl? I didn't see a mention of your reasoning to heat the crawl in your original post.

 

[LLigetfa]

Ja, it is real nice not to have cold floors. No need for bunny slippers.

http://www.globaltextiles.com/html/images/upload/tradeleads/554/553869.jpg

 

[Hass]

I wanted to heat my crawl too... I wanted to put vents in my floor actually, and use an OAK (pull air up through OAK, then air will flow down vents to replace it), or just use through the wall/floor fans to blow it down.

But then I thought about bugs crawling up, the yuckly smell, and radon.
My crawlspace is only a single block high with no access.... Dirt floor (covered with 6mil poly of course).
If none of the 3 are a problem with your crawlspace, then go for it

 

[LLigetfa]

If none of the 3 are a problem with your crawlspace, then go for it

None of the 3 are an issue for me. I built on clay so no radon. I have a good stone base under the slab with draintile. I have a duct from the sump pit to the HRV to take away humidity and any possible odour.

Hass, you could go with one of the options that I posted. Run a duct from a room back to the stove through the crawlspace. If the room is warmer than the crawlspace, it will transfer some of the heat yet not exchange the air.

In my former home, I had a crawlspace that was just poly over dirt. I tried using a blower to suck hot air from the stove and blew it to a back room through a duct. By the time it got back there it was cold but it did warm the crawlspace along the way. In this house I did it the other way around, bringing cold air to the stove.

 

[begreen]

We have a before and after comparison with our house. Before the remodel and new foundation we had a leaky ventilated crawlspace. I closed off the vents in winter, but the sill plate still had lots of gaps. Now we have a full perimeter poured foundation, good vapor barrier, 3' more head room and a sealed and insulated conditioned crawlspace. The difference is very noticeable, especially the warmer floors. It has never dropped below 60F down there even with temps in the teens.

 

[boisblancboy]

Sounds like it would help a lot. I've been in many homes that were cold because of a cold crawl. In fact, a friend of mine has a house in your neck of the woods (suttons bay, MI) that has that issue. He only spends a week per winter there, so isn't inclined to do something about it.

I see MANY homes with cold bedrooms that stick out over unseated garages- a classic problem. I think your idea will work to warm the crawl.

Out of curiosity, is your floor cold? Is that why you want to heat the crawl? I didn't see a mention of your reasoning to heat the crawl in your original post.

Yeah I have not cold, but fairly cool I would call it. The temp in the crawl space generally is between 47-52 degrees.

 

[boisblancboy]

Ja, it is real nice not to have cold floors. No need for bunny slippers.

http://www.globaltextiles.com/html/images/upload/tradeleads/554/553869.jpg

Love the slippers! LOL

What type of fans would you recommend?

Do you think there would be much difference between pulling the cold air from the crawl to the stove or pulling hot air from the stove to the crawl?

 

[LLigetfa]

What type of fans would you recommend?

Do you think there would be much difference between pulling the cold air from the crawl to the stove or pulling hot air from the stove to the crawl?

I think a bigger fan run on a lower speed would be quieter than a small fan running flat out. I use a 650 CFM 8" inline centrifugal duct blower with a variable speed control. I would never consider sucking air from the stove and blowing it into the crawlspace. I'd be worried about dust buildup and sucking up an ember, sparking off a fire.

IMHO, cold air being more dense is easier to move. Cold air can also be safely filtered. I built a large box to house the blower and have a 16"x25"x1" 3M Filtrete furnace filter between the blower and the stove. I also put a washable prefilter before the blower to reduce buildup on the fins.

I don't want to put too much heat into the crawlspace, so sucking out the coldest air works for me. The make-up air is drawn from floor level of the living space above so it becomes a natural cold air return that goes with natural convection rather than against.

 

[boisblancboy]

What size foot print is your crawl space that your heating?

 

[LLigetfa]

1200 sq ft. in an El shape. The fireplace is in the El.

 

[boisblancboy]

Thanks for the help!! I dont plan on doing it this year, hopefully next year.