Condensation on Wood Stove / Outside Air Piping

[cjmoran]

Hello.

I had a wood stove installed a few years ago. The stove is a Quadra-Fire Explorer II. When I was inspecting the wood stove earlier this year, I noticed a significant amount of surface rust on the bottom back of the stove. I didn't understand why there was so much surface rust build up. I cleaned the rust from the stove the best that I could.

Today I am using my wood stove and took another look at the areas that are rusting. There is condensation all over the areas that are rusting as well as the outside air intake piping. This outside air tube is metal and is very cold as it's a very cold day. The tube is conducting the cold directly to the back of the stove and I'm getting condensation all over.

I'm wondering what my options are. I suppose I could get a dehumidifer, but my home humidity is at 34% which I don't know if I really want to drop. Another option might be to eliminate the outside air connection entirely, but I don't know how well the stove will operate without it. I also don't know if code would allow that. Another option might be to replace the metal intake tubing with a different tube that has higher thermal resistance. A last option might be to better insulate the outside air tube. A majority of the tube length runs under a firebox from a previous fireplace. 3 feet of the length is directly exposed to outdoor temperatures (it's in a chase).

Any ideas? I've also asked my installer for ideas.

Thanks.

 

[begreen]

Similar to comments here. Insulating it sounds most practical.
https://www.hearth.com/talk/threads/outside-air-kit-oak-insulate-pipe-or-not.159606/

 

[electrathon]

Insulated plastic would condense far less than insulated metal.

 

[rwhite]

Is the OAK required for your set up? Have you tried running without it?

 

[cjmoran]

Thanks for the replies.

My installer emailed me back this morning and they recommended try running without the outside air kit. I'm going to disconnect it and see how well the stove runs. If that doesn't work, they suggested putting spray foam insulation in the chase where the outside air kit tube runs. I'm wondering if the tube should first be wrapped with insulation and then maybe a vapor barrier of some sort wrapped around it? Maybe that's not necessary. I suppose spray foam insulation by itself would be equivalent to wrapping the tube. Lastly, maybe a plastic or other tube instead of the metal so it doesn't conduct the cold as much. Maybe both the insulation and a different tube would provide the ideal solution.

 

[webby3650]

This is why we rarely run outside air for stoves. It seems to introduce more problems than it solves. Ice cold air all winter, hot humid air in the summer, rusty stoves...

 

[cjmoran]

Hmm. So you install stoves yourself and you avoid using outside air kits if possible? I'm running the stove now without the outside air kit and it seems to be running fine. Had some initial difficulty getting the fire started, but I don't think it's any more than usual. It seems to be running at the same rate with and without the outside air tube connected. My home was built in 2007, so it may be more 'air tight' than older homes (I don't know), but doesn't seem to matter in my case.

I've read things about problems created by not having outside air kits (toxic air, drawing heated air from your home to the outside, etc..). Not sure how much truth there is to these things and if it's applicable to my situation.

 

[electrathon]

Yes, the stove may operate just fine without the outside air direct connect. The issue is not the operation of the stove, it is the air being drawn into the house from other places. The chimney creates a suction on your house. The outside air is drawn in through any place it can find. Bad door seals, leaky Windows, leaky electrical boxes, backdrafting through your water heater or furnace chimney, etc. Many people on here recommend you allow for the house leakage to provide for the air to the fire. The 15 or so cubic foot per minute air draw on your fireplace is a lot of air infiltration into your house, 200 cubic foot per minute is about normal so this is almost a 10 percent added heat loss to your house.

The ice and frost are from the moisture in your house sticking to the poorly insulated/installed outside air duct. Installs it proper/well and the issue will be fixed. Disconecting it means you will need to heat 15 or more CFM of air in your house. Tremendous waste of energy, possibly livability if the cold air is being drawn in from the far side of the house. You will be able to control the cold air infiltration if you install it right, disconnect it and you just make more heat loss on your house.

 

[electrathon]

I've read things about problems created by not having outside air kits (toxic air, drawing heated air from your home to the outside, etc..). Not sure how much truth there is to these things and if it's applicable to my situation.

Totally applicable, but only an big issue when the fire is going.

 

[rwhite]

Yes, the stove may operate just fine without the outside air direct connect. The issue is not the operation of the stove, it is the air being drawn into the house from other places. The chimney creates a suction on your house. The outside air is drawn in through any place it can find. Bad door seals, leaky Windows, leaky electrical boxes, backdrafting through your water heater or furnace chimney, etc. Many people on here recommend you allow for the house leakage to provide for the air to the fire. The 15 or so cubic foot per minute air draw on your fireplace is a lot of air infiltration into your house, 200 cubic foot per minute is about normal so this is almost a 10 percent added heat loss to your house.

The ice and frost are from the moisture in your house sticking to the poorly insulated/installed outside air duct. Installs it proper/well and the issue will be fixed. Disconecting it means you will need to heat 15 or more CFM of air in your house. Tremendous waste of energy, possibly livability if the cold air is being drawn in from the far side of the house. You will be able to control the cold air infiltration if you install it right, disconnect it and you just make more heat loss on your house.

How long does it take to get to that 15cfm. I could see an issue if a person left doors shut all day long but it would seem normal entry and exit would more that create enough make up air for a wood stove.

 

[electrathon]

How long does it take to get to that 15cfm. I could see an issue if a person left doors shut all day long but it would seem normal entry and exit would more that create enough make up air for a wood stove.

60 seconds= 15 cubic foot per minute. About the capacity of air in a refrigerator every minute. Once the fire is going you have draft, so for the first few minutes it is less, then the draft starts and 100 percent of the air that goes up the chimney is sucked in from someplace. If the install is ideal, it draws it from outside, poor install and it draws in through wherever the path of least resistance is.

 

[webby3650]

Hmm. So you install stoves yourself and you avoid using outside air kits if possible? I'm running the stove now without the outside air kit and it seems to be running fine. Had some initial difficulty getting the fire started, but I don't think it's any more than usual. It seems to be running at the same rate with and without the outside air tube connected. My home was built in 2007, so it may be more 'air tight' than older homes (I don't know), but doesn't seem to matter in my case.

I've read things about problems created by not having outside air kits (toxic air, drawing heated air from your home to the outside, etc..). Not sure how much truth there is to these things and if it's applicable to my situation.

The outside air is a good thing don't get me wrong. Especially in new Homes. In my area, most people want the stove for emergency heat or a weekends only kinda thing. So the OAK is just a cold air infiltration point for these people. Then there's the constant condensation issue as you are finding out. I personally don't have OA on my stoves because my house is on the loose side and have never seen the need for it.

 

[cjmoran]

The outside air is a good thing don't get me wrong. Especially in new Homes. In my area, most people want the stove for emergency heat or a weekends only kinda thing. So the OAK is just a cold air infiltration point for these people. Then there's the constant condensation issue as you are finding out. I personally don't have OA on my stoves because my house is on the loose side and have never seen the need for it.

OK. Thanks for the info. I guess I'll just need to make a decision. There seems to be two lines of thought regarding the outside air kit from what I've read. I would prefer to have it hooked up and to me it makes sense to have it, but I may go without it. It is not our primary heat source and we use it periodically on really cold days or the weekends like you mentioned. Also, my installer appears to want to charge me for fixing it and better insulating the outside air kit, which I don't know if I want to pay for, or should have to pay for.

 

[electrathon]

The outside air is a good thing don't get me wrong. Especially in new Homes. In my area, most people want the stove for emergency heat or a weekends only kinda thing. So the OAK is just a cold air infiltration point for these people. Then there's the constant condensation issue as you are finding out. I personally don't have OA on my stoves because my house is on the loose side and have never seen the need for it.

Ok, I have a question about your post. I am not trying to be snide, just really curious. You said that the stove is installed without outside air because it is a "cold air infiltration point" so people choose not to have it. Isn't the chimney a warm air extraction point? The chimney extracts very close to the same amount to air as the OAK lets in. The chimney lets it out so you are less aware of it, but it is there just the same. But I don't see installers recommending bypassing/under sizing the chimney. If your house is on the loose side I would think you would want the extra 15 CFM of heated air Gaines by a direct connect air source. Non-connected air source I totally see your point (and am befuddled why anyone would buy the stove).

 

[electrathon]

Also, my installer appears to want to charge me for fixing it and better insulating the outside air kit, which I don't know if I want to pay for, or should have to pay for.

You are correct, you already paid for instalation, you should not have to pat again for him to do it right. But, you can do it for about $50 for a bag of Roxul bats and some visquene. Not that complex and since the guy did it poorly last time he may not do it better next time.

 

[webby3650]

You are correct, you already paid for instalation, you should not have to pat again for him to do it right. But, you can do it for about $50 for a bag of Roxul bats and some visquene. Not that complex and since the guy did it poorly last time he may not do it better next time.

How will you insulate the outside air duct with roxul bats and plastic?

 

[webby3650]

Ok, I have a question about your post. I am not trying to be snide, just really curious. You said that the stove is installed without outside air because it is a "cold air infiltration point" so people choose not to have it. Isn't the chimney a warm air extraction point? The chimney extracts very close to the same amount to air as the OAK lets in. The chimney lets it out so you are less aware of it, but it is there just the same. But I don't see installers recommending bypassing/under sizing the chimney. If your house is on the loose side I would think you would want the extra 15 CFM of heated air Gaines by a direct connect air source. Non-connected air source I totally see your point (and am befuddled why anyone would buy the stove).

When the stove is it in use, it makes the stove and area around it colder. Frost and condensation form on and around the OAK. The alternative is a hideous insulated pipe laying behind the stove. In a new construction senerio, straight down through the floor would be ideal. Very rarely is this possible in a retrofit situation like we deal with almost always.

 

[electrathon]

How will you insulate the outside air duct with roxul bats and plastic?

Sorry, I was thinking this was the other post that has a similar conversation. His duct was ran in with a piece I'd ftex furnace duct (I think, from the pics).

Depending on location it may take a little more. If the duct is primarily hidden I would wrap the duct with insulation and wrap that with a vapor barrier to hold back moist ain't and keep it neat. If the duct is visible it would be better to have a nice raceway.

 

[electrathon]

When the stove is it in use, it makes the stove and area around it colder. Frost and condensation form on and around the OAK. The alternative is a hideous insulated pipe laying behind the stove. In a new construction senerio, straight down through the floor would be ideal. Very rarely is this possible in a retrofit situation like we deal with almost always.

OK, form over function. It looks better without the ductwork to the stove, I get that. The pipe is cold though because the outside air is cold. It enters the house on the way to the stove. The pipe absorbs some heat out of the room as the air is traveling through it. Here is the rub though. The cold radiating off the pipe is peanuts compared to the cold air being drawn into your house through air leaks all over without an OAK. Only real difference is that the pipe is cold near to the hot stove, the air leaks in all over the house, like in distant bedrooms that are already cooler. I doubt anyone would be able to pin down this issue, but the common issue brought up is that people have trouble getting heat to the far side of the house. No outside air contributes big to this problem. If you have a single room, overheat all rooms, etc then it really is mute, but if your far rooms are cool it really needs to be looked at hard.

 

[cjmoran]

OK, form over function. It looks better without the ductwork to the stove, I get that. The pipe is cold though because the outside air is cold. It enters the house on the way to the stove. The pipe absorbs some heat out of the room as the air is traveling through it. Here is the rub though. The cold radiating off the pipe is peanuts compared to the cold air being drawn into your house through air leaks all over without an OAK. Only real difference is that the pipe is cold near to the hot stove, the air leaks in all over the house, like in distant bedrooms that are already cooler. I doubt anyone would be able to pin down this issue, but the common issue brought up is that people have trouble getting heat to the far side of the house. No outside air contributes big to this problem. If you have a single room, overheat all rooms, etc then it really is mute, but if your far rooms are cool it really needs to be looked at hard.

I'm struggle to understand if insulating the OAK duct will really fix the problem. If the cold air still makes it's way through the pipe, through the stove, and back out the chimney, I would think it would still be cold even if it's insulated. The cold will still conduct to the back of the stove, and I'll still get condensation. It's temperature will just be more isolated from whatever is on the other side of the insulation. Just because it's wrapped in insulation doesn't mean it will not get very cold. Is that right? Maybe there's something I'm missing and I don't understand the thermal dynamics. Note that the chase that the outside air kit is in is behind a metal panel that sits behind the stove. I don't know at want temperature the chase will regulate at. It's not in my home. It's in the chase are under where the chimney liner goes up, under my old pre-fab firebox that the stove now sits in front of.

 

[cjmoran]

I'm struggle to understand if insulating the OAK duct will really fix the problem. If the cold air still makes it's way through the pipe, through the stove, and back out the chimney, I would think it would still be cold even if it's insulated. The cold will still conduct to the back of the stove, and I'll still get condensation. It's temperature will just be more isolated from whatever is on the other side of the insulation. Just because it's wrapped in insulation doesn't mean it will not get very cold. Is that right? Maybe there's something I'm missing and I don't understand the thermal dynamics. Note that the chase that the outside air kit is in is behind a metal panel that sits behind the stove. I don't know at want temperature the chase will regulate at. It's not in my home. It's in the chase are under where the chimney liner goes up, under my old pre-fab firebox that the stove now sits in front of.

Here's a picture of the back of my stove and back panel that the outside air tube runs through (disconnected from the stove in the picture).

 

[electrathon]

The condensation comes out of your house air. The humidity is very low outside when it is very cold. The pipe being insulated and vapor barrier end is to keep inside the house air away. This issue is very similar to a glass of ice water dripping water on the table, the water dripped is out of the air, not the glass. When the cold air enters your stove there is usually some heat right at the stove to repel the water formation. The cold air that enters your stove is quickly heated and is the combustion air for the fire. Heated air them moves up the chimney.

 

[electrathon]

Not sure about your specific stove, but switching the metal tube to plastic would help with thermal transfer, that will help with condensation. I am not sure about the surface temp on your stove there (mine is always cool) or if there is possibly a code issue with running plastic to the inlet.

 

[cjmoran]

The condensation comes out of your house air. The humidity is very low outside when it is very cold. The pipe being insulated and vapor barrier end is to keep inside the house air away. This issue is very similar to a glass of ice water dripping water on the table, the water dripped is out of the air, not the glass. When the cold air enters your stove there is usually some heat right at the stove to repel the water formation. The cold air that enters your stove is quickly heated and is the combustion air for the fire. Heated air them moves up the chimney.

I understand your explanation. But even if I wrap the portion of the pipe that is both in the chase as well as inside my home with both insulation and a vapor barrier, the back of the stove will still be cold when it's not in use. I not only get condensation on the OAK tube, but also the stove itself. The entire back bottom of my stove is covered with condensation when the pipe is connected to the stove on a very cold day. The cold is transferred to the stove itself through thermal conduction. I am thinking that even if I insulate and wrap the pipe that the tube will still be as cold as it was before because there is still outside air running through it. That cold metal will bring down the temperature of the back of my stove where it connects to the pipe. I'll still get condensation on the stove itself when I'm not using it. Right? I think the only way to fix the problem is to eliminate the connection between the metal tube and the stove some how, or replace the tube with a new tube that has a metal interior layer, thermal barrier, and non thermal conductive outer exterior that attaches to the stove. That will thermally isolate the condition of cold to the back of the stove.

 

[cjmoran]

I understand your explanation. But even if I wrap the portion of the pipe that is both in the chase as well as inside my home with both insulation and a vapor barrier, the back of the stove will still be cold when it's not in use. I not only get condensation on the OAK tube, but also the stove itself. The entire back bottom of my stove is covered with condensation when the pipe is connected to the stove on a very cold day. The cold is transferred to the stove itself through thermal conduction. I am thinking that even if I insulate and wrap the pipe that the tube will still be as cold as it was before because there is still outside air running through it. That cold metal will bring down the temperature of the back of my stove where it connects to the pipe. I'll still get condensation on the stove itself when I'm not using it. Right? I think the only way to fix the problem is to eliminate the connection between the metal tube and the stove some how, or replace the tube with a new tube that has a metal interior layer, thermal barrier, and non thermal conductive outer exterior that attaches to the stove. That will thermally isolate the condition of cold to the back of the stove.

Another option might be to put an intermediate non-thermally conductive pipe between the stove and metal piping that goes out the panel, but I don't know if that's up to code (if a hot ash could somehow make it's way out the back into the OAK tube).