Vented or Unvented crawl space?

[Nevada_Mike]

I know the new age old question.  My foundation is entirely above ground.  Concrete footing with a 6 inch concrete stem.  The remaining stem wall is constructed out of wood.  It is set on well drained rock pad. My house is the Alaska Cabin in the gallery.  I am thinking about insulating the stemwall,  installing good vapor barrier on the ground and having no exterior vents.  I would use a outside air kit on the wood stove that draws from the crawl space and install an open register in the opposite corner of the house creating a flow through.  The house will sit unheated much of the year. What do you think?

[JRR]

I think the plan is good.  But you may want to consider piping the woodstove air make-up all the way from the outside register.  This would cause less temperature variation in crawl space ... keeping the floor above more even temp ...especially if the pipe were insulated.  

Of course, depending on the rest of your insulation plan,  this may not be a concern.

[Nevada_Mike]

Do you mean get the wood stove intake air from the outside of the structure.  I thought that the draft from the stove would draw warm air into the crawl space through the open floor register on the other side of the house space causing the two spaces to be closer in temp.

[glenn kangiser]

I see what your idea is Mike.  I used to build wood stoves that had this capability.  We would leave a baffle out  of the bottom - the base being like an upside down square funnel.  We would sit it over a register which was connected to the back rooms by ducts, drawing the cold air out of the back rooms at floor level, and if doors were open it would draw the warm air into them throughout the house.

What you are proposing should work in a similar manner depending on stove type and what shrouding  you do around the stove.  Natural tendency would be for the air above floor level to short circuit to the base of the stove and rise as heated, leaving the heavier colder air in the crawlspace without a shroud to make it suck from below.  The stoves we made had dual walls and fins every 6 inches to move more air through convection.

I don't know how good or bad your plan is as I haven't tried or studied on that - just the action of the stove and air.  Maybe the others can give more input on that.

[John Raabe]

Mike: I expect you have read this recent thread on  a very similar topic - http://countryplans.com/cgi-bin/yabb/YaBB.cgi?board=01;action=display;num=1116048795

I think you have a reasonable plan.

Here's what I might do to give you the flexibility to adjust the options and perhaps maximize the control you have.

Seal and insulate the crawlspace walls and provide a good moisture barrier at the soil as you suggest. Have one or two opening vents in the pony wall that can be closed or open to experiment with bringing in outside air. Position them so they can provide some cross ventilation when open.

Now provide another operable vent under the wood stove and consider using this as a fresh air intake. I like your idea of using the soil to preheat this intake air in the winter time as well as freshening the crawlspace air.

Now, you will have to see if the draw of the wood stove is sufficient to pull this air from the CS or if you need more of a direct vent to keep from back-drafting the stove when the house fans and dryer are on. This is a problem I can demonstrate in my house. When there is no fire lifting the chimney air, my house fans can pull air down and I get the smell of the chimney back into the house through the stove. (Note: I have an old cast iron stove that has no outside air intake port. A more modern stove with vented air would probably not have the problem.)

If needed you could install a small air pump to pressurize the CS air.

With this system you could also open the side vents in summer to provide seasonal airflow when preheating the stove air is not needed. Thus you can have a completely sealed crawlspace or a partially vented one and see what gives you the best performance.