Heat loss when woodstove is off

[evilgriff]

Question: If you don't have a damper on your woodstove and you don't have an OAK, what keeps you from losing heat when the stove is not on? Does an OAK prevent heat loss?

 

[DexterDay]

An OAK wont prevent loss while its not running.. (for the stove)

Heat loss comes in numerous forms. Insulation (or lack there of) is a common form of heat loss. Something that an OAK will not make up for.

 

[evilgriff]

Dexter, My stove takes air in from the room and sends it up the chimney when the stove is running. Doesn't it do the same thing when it is not running? For instance, it is 55 degrees outside, too warm for my stove so I let the furnace do the job. Isn't there a continuous draft from the stove going out the chimney right now?

 

[fossil]

My guess would be that with the stove door shut, and the primary air control set to minimum, the amount of warm room air being lost through the stove & up the flue (assuming that's what you're worried about) over the course of 24 hours would be completely overshadowed by opening an outside door long enough to step through it once. That's my guess, and I'm stickin' to it. Rick

 

[DexterDay]

While running, its drawing air..... When its not running.... Its not. It may actually be doing the exact opposite.

Ever heard of the chimney effect?

 

[evilgriff]

Rick, yup that's what I was thinking about. This is why I usually make my whole family leave the house at the same time to keep from opening the doors too much (ha ha). Thanks for the reply, looks like I have nothing to worry about. And dexter, nope, never heard about the chimney effect- went to wikipedia and read about it. I have the general idea. Not even going to consider calculating the loss with those formula's listed. The math courses I would need would cost more than the oil I would burn in a lifetime. Thank you both for the reply's.

 

[semipro]

Question: If you don't have a damper on your woodstove and you don't have an OAK, what keeps you from losing heat when the stove is not on? Does an OAK prevent heat loss?

Depends. If your house is under positive pressure for some reason and you don't have an OAK, yes, conditioned air could be pushed through the stove out the chimney. With an OAK installed this effect would be minimized.

On the flip side, if you have an OAK but you're not using the stove cold air could pass through the stove either going in the OAK and out the flue or vice versa. The cold air passing through would cool your stove and suck heat (not hot air) our of your house. I've seen this occur.

Actually, one of the benefits of an OAK that I've discovered is the mitigation of the firebox smell entering our house during periods of damp weather. We used to smell ashes very strongly before installing an OAK. Now that smell exits the house via the OAK inlet outside.

I've always wondered if installing a cable operated damper at the top of a flue and/or another at the OAK would be a good way to address this issue.

 

[Wood Duck]

While running, its drawing air..... When its not running.... Its not. It may actually be doing the exact opposite.

Ever heard of the chimney effect?

I have heard of the chimney effect, and it probably pulls air up the chimney all winter assuming that the stove room is heated above outside temperature. With the damper closed you may not lose a lot of air up the chimney, but I'd say there is definitely a force pulling air up the chimney all the time. With the damper closed that force likely can't pull a lot of air, but it is still there. With an OAK you'd have the slightly warm inside of the stove (warmed by the temperature of the room heating up the stove) that is still warmer than outside. This would cause the more bouyant air in the stove to rise but with the OAK it would pull outside air into the stove rather than room air. However, this might make the stove cold and the cold stove could chill the room a little. I have an OAK and haven't moticed that the stove is particularly cold, but my stove room tends to be quite chilly when the stove is not burning.

 

[jharkin]

This has been discussed on here before - I don't think you have anything to worry about. The draw up the chimney is caused by temperature differential. Many folks have trouble getting good strong draw until there flue heats up to at least a few hundred degrees. How much draw is there likely to be when the temp differential is only 20 degrees? And its got to pull all that air through the tiny air intake (which is probably smaller in area than the cracks around your entrance door).

Going by the numbers, Ive read that the draw of a burning EPA stove is surprisingly small - something like 10-20 CFM. And this is with a raging hot fire. How much can it really be pushing cold?

 

[corey21]

I really don't think you are going to lose much heat up your chimney if you do it is a very small amount.

 

[Slow1]

When adding the OAK into the debate consider that not every stove has the OAK sealed to the intake of the stove - i.e. it may just feed air "near" the stove's intake meaning that essentially you have an open pipe into the house with the oak and a gap there near the stove's air inlet. With this design you don't have a sealed system; rather you still have air flowing up the chimney (assuming you have a minimal draft) and the air may or may not be pulled from the OAK - it may be that the air from the outside is being pulled in through the OAK at a different rate - perhaps higher or lower depending on the overall air pressure in the home (it could even be flowing out the OAK unless there is a damper of some sort).

 

[TradEddie]

Two effects, Stack Effect, and Chimney Effect. It's actually much the same effect (hot air rises), just happening in different places, the Stack Effect causes lower floors of a building to be at slightly lower pressure than outside, and the upper floors to be at higher pressure than outside. The stack effect causes any leak in a lower floor to draw air in from outside, so if you don' have an OAK, cold air will be drawn down the chimney into the room, (back up the stairs and out the attic or upper floor leaks). Hot air is trying to rise, but the entire house acts like a chimney too, and that's a much bigger flue...This is why you can get smoke coming into a room when you light a fire, and why cracking a door solves the problem (easier path for air to come in).

If you have an OAK, and the stove is totally sealed from the room, then it is likely that the Chimney Effect will draw cold air in the OAK and up the chimney, and cool the room by cooling the stove surface. Who knows which cooling effect is bigger? They both exist, and probably a half-dozen other factors too.

Take a look at his picture : http://www.flickr.com/photos/oracleondelhi/3331612999/
You can see the wrapping being sucked in the bottom and out at the top. Your house is doing the same all the time. When the stove is lit, without an OAK you need to overcome the stack effect in the whole house, by having a much greater temperature difference.

Who'da thunk that burning wood was so complicated?

TE