How does length of an air intake affect performance -- I have a crazy idea

[rashomon]

I know this idea may immediately get shot down, but I'm trying to see if it could work. I own a Green Mountain 60 with a 18' double insulated chimney that rises straight up from the stove, no turns.

I know this stove can have an outside air accessory. My dealer didn't seem to think I needed it, when I asked there wasn't much thought. (Some may recognize my username with a recent issue I was having. That has been fixed. I was burning wet wood and my chimney cap spark arrestor was completely clogged after only 2 months of use and I didn't realize it. I have a new cap due to possible wind issues, I am intentionally burning hotter with drier wood, and my issues have gone away. Anyhow this isn't why I'm considering an outside air intake.)

Our basement is freezing. Previous owners installed baseboard heating because: 1) the space finished but rarely used, same with us; 2) the registers for forced air are at the ceiling and there isn't adequate return air to cycle the cold air.

The stairwell to the basement is wide open with no doors. In that way our basement acts like a cold trap as all the cold air falls down the stairwell. At the opposite end of the stairwell is our stove.

I was thinking about sending a pipe down under the stove and attaching it to the air intake on the stove (possibly with a flap to bypass the pipe if the length would cause issues). The pipe would extend all the way to the the floor of the basement pulling air from there. In this manner I would hope to warm the cold basement air which would allow warmer air to travel down the stairway to replace what the stove pulls in. This could also create a cycling of moving air.

What would be really cool is if instead of feeding the air intake on the stove I were to simply attach the pipe to a heat exchanger metal box on the side of the stove. This way as the stove slowly heats it would warm the air at the top of the pipe creating a thermosiphon.

People have posted something similar on youtube, like this one. But my idea wouldn't change the chimney at all. Two immediate thoughts are 1) maybe it needs higher EGT to activate the needed thermosiphon air flow, and 2) is the length of mine extending into the basement too much for a thermosiphon.

I'm looked at "pass-through registers" but they only suck up the warm air at the ceiling and so aren't really effective. I've also considered an active system which may be the only option if I wanted to do this. Of course maybe it's simply not worth it.

Has anyone seen such a thing?

 

[armanidog]

You could do an experiment and use some flexible tubing such as 4 inch dryer vent pipe. Put it down the stairs and hook it up to the outside air intake on your stove. See if it pulls the cool air up from the basement. Maybe check the temperature every few hours in the basement and see if it warms up at all.

 

[begreen]

Combustion air can not be taken from the basement. It must be outside air. If there are any combustion devices like a furnace, boiler, or gas/oil HW heater in the basement, there could be harmful consequences doing this. The outside air can only come from outside, or a fully ventilated crawlspace.

Creating more negative pressure in the basement will not pull down enough heat to counteract the heat loss. If the basement walls are uninsulated, that is a good place to start after sealing any leakage at the sill. Then, a space heater may suffice.

 

[EatenByLimestone]

Yeah, the makeup air will be pulled from around the sill plate and rim joist. Heat doesn’t like to sink.

 

[rashomon]

experiment and use some flexible tubing

I would try this if the stove wasn't on the other side of the house from the stairwell, it would end up being a 60ft stretch that's mostly horizontal. If I do an experiment I'll report back though.

It must be outside air. If there are any combustion devices like a furnace, boiler, or gas/oil HW heater in the basement, there could be harmful consequences doing this.

Thanks for this consideration. Although, currently my stove has no outside air hookup. It just sucks up the air in the room. I asked my dealer if I should consider outside air and he brushed it off like this wasn't necessary. If I had a similar stove in my basement wouldn't that do exactly what you're cautioning against? Your point makes sense but it mustn't be that big an issue if they didn't require it already.

Yeah, the makeup air will be pulled from around the sill plate and rim joist. Heat doesn’t like to sink.

This does make sense. I want to insulated the rim joists because I imagine that's where a lot of heat goes.

 

[begreen]

If I had a similar stove in my basement wouldn't that do exactly what you're cautioning against? Your point makes sense but it mustn't be that big an issue if they didn't require it already.

This depends on the house. The negative pressure potential exists in many basements. That's why we get so many basement install problems showing up here. If the goal is to bring outside air to the stove, run a duct to the nearest perimeter wall and out between the joists. Upsize the duct if the run is long.

 

[MongoMongoson]

Also, even if you could pull air from the basement, consider how little air you would be moving. it is the amount of air required for combustion which isn't very much at all compared to the volume of a basement. You would not move enough to make a difference.

 

[rashomon]

Also, even if you could pull air from the basement, consider how little air you would be moving. it is the amount of air required for combustion which isn't very much at all compared to the volume of a basement. You would not move enough to make a difference.

Yeah, I think I’ve been convinced against it which is releasing. I’m a tinkerer and could easily have wasted tons of time and left holes in my floor trying to make this work. In the end money and time better spent would be to insulate the rim joists.