I can't see this plan working at all, I don't believe you'll get warm air to flow down without a fan or duct booster. The stove will draw all the air it needs from infiltration, either from the room it's in or the crawl space - But, you won't get the warm air to 'flow down' to replace the cold, more cold will infiltrate to replace whats being drawn. Warm air in any useable ammount just will not flow down, it needs to be forced.
Nope I dont think natural convection will work trying to get it to go down either. I want it to go up. I wanted it to draw the cold air from the downstairs portion of his house. If the cold air isn't allowed to just settle down there but has some place to go ( back to the stove) it will feel warmer down there because the cold air isnt stacking up down there or in the stairway.
I coverd the problem of air infiltration from outside when I mentioned the 3 X 12 register in the wall downstairs next to the floor .
Unless the crawl space is absoulutely sealed against outside air, that is what will be pulled into the crawl space! not the warmed air from the main floor that is expected to to flow down (reverse) into an area of heavier air. In effect you will be creating a vacuum and the coldest air available and at the lowest elevation has the most potential to flow into the crawlspace. Makeup air for combustion has to come from someplace. It comes into your house on the pressure differential between the top of your chimney and the coldest most available air. This pressure differential will be much higher than what you will get from your proposed convection system.
Really I think what you will need to do is pressurise the crawlspace with a fan to keep cold air from collecting there. Then make outside air available directly at your stove instead of having it pulled in at the most harmfull of places.(crawlspace)
Nope warm air isnt going to go
down through the vent pipe into the crawlspace on it's own. That's not even how I thought I had explained it. Warm air is going to draw the cold air up and out of the crawl space. The crawl space needs to have a 3" X 12" register type vent from the room downstairs to the crawl space.
Basic premise: As the air in the pipe, behind the stove, gets heated it will rise ( the air will rise, not the pipe ) . This rising air will draw cold air from the crawl space and be replenished by the cold air next to the floor of the lower level from through the register/vent/return installed.
Simple convection applied to a larger area than a single room. We arent talking about pulling combustion air from the crawlspace. I was talking about recurculating air through his house to more effectively warm the lower level by putting in a cold air return to his wood stove's heating area. Not to the combustion chamber.
He needs a cold air return from the lower level returning air to the wood stove. He wants to warm the crawl space to keep pipes from freezing. If I was doing it I wouldnt want to hear a fan or worry about the electricity going out. I would put it in just as I described as a cold air return from the lower level of his splitlevel home to behind the woodstove.
If you thought I meant for the vent pipe to barely penetrate above the floor behind the stove think again. I mentioned that it needs to stick up and run parralell to the flue pipe to be heated by it. The higher and closer the better. The heat in the flue pipe is considered wasted heat once it exits the living area. I'm not trying to recover all the heat from it and introduce a creosote problem. Just recover enough of it to create a draft to pull cold air from a lower level than the bottom of the stove.
If you want a fan to push air down there put one in or set it ar the top of the stair and try pushing it down there. Let me know how that works for you. I have an aversion to the noise, was why I thought of using natural convection to draw cold air out of his downstairs, warm it behind his stove and keep doing it without electricity.
I'm sorry if I am not able to explain it well enough that it has become a question of if warm air rises or falls. We all agree it rises. What is so hard to understand that it will rise up the 6 - 8 foot vent pipe behind the stove and pull cold air from the crawl space? The air that is being drawn from the crawlspace gets replenished through the 3 x 12 register vent in the wall of the room that adjoins the crawl space. As this cold air from down stairs gets pulled out of that room it gets replenished by warmer air from the upper level where the wood stove is located. The wood stove is heating the air in the room and the air that is rising up the vent pipe. This rising air is drawing more air from the crawl space. Which starts the cycle over again. As the air in the crawl space gets warmer, the heated vent pipe will draw it from down below easier.
Warm air rises, cold air falls. Make the rising air work for you. Have it pull up cold air that settles downstairs.
Here goes nothing. I will try explaining this in reverse. After that , I am done, If you dont think the warm air will rise then put a fan in there and force it against its will to the cold room down stairs.
You heat air from the wood stove it travels through the house and cools. As it cools it settles in the lowest part of the house. Which is down stairs from the wood stove. By puttin in a register at the bottom of the wall down stairs, The wall that adjoins the crawlspace, and a hole just behind the wood stove we now have a path for the air to travel. We just dont have any force to move it. Put some vent pipe in the hole. Heat the top of the vent pipe with the wood stove or hot flue pipe and the warm air in the pipe will start to rise. As the air that rises comes out of the pipe it cools and goes through the house and back down stairs where it is drawn into the register and into the vent pipe again. It does this untill stove isnt making enough heat to create a sufficient draft in the vent pipe to continue moving air.
The down stairs will be warmer because we are moving the cold air out from there back to the heated area of the woodstove. The crawlspace will be warmed keeping his pipes from freezing. It might not be warmed to 75 degrees but it isnt a living area and as long as the pipes don't freeze , it is warm enough.