Is a wood stove ever safe when your central furnace is running?

[Burnhaven]

Our situation is a bit complicated, but in any typical home, the wood stove can die out overnight. If the weather is really cold, you don't want to shut off your furnace and wake up to a 25F degree house.
I'm told all interior stove pipe leaks at the joints and furnace cement will not last. So normally the joints suck in room air -- no problem. When the fire dies out the flow may reverse.

Now with double-walled pipe, if the joints are leaking air into the room, where is that air coming from if the outside pipe and inside pipe are isolated from each other? I have an outside air kit.

The two layers of DSP HAVE to be isolated from each other, otherwise hot stove exhaust would heat up the outside pipe and violate its clearance specs.

So the air being drawn in CANNOT be from the stainless inner liner, or the chimney -- that would smell along with violating the whole idea of DSP. If being pulled from the fire box it would also smell. So can it be coming from the outside air kit, which would explain fresh, cold, odorless air.

Our specific situation is described in detail here:

https://www.hearth.com/talk/threads/wood-stove-in-two-suite-home.138030/

 

[bholler]

So the air being drawn in CANNOT be from the stainless inner liner, or the chimney -- that would smell along with violating the whole idea of DSP. If being pulled from the fire box it would also smell. So can it be coming from the outside air kit, which would explain fresh, cold, odorless air.

No it is coming from inside the pipe. To start your joints are not together all the way that might help if you can seat them all the way. Also where is your return located? it should not be right by you stove. But to answer your question if you hvac system is balanced and your stove is installed properly there is no reason you cant run both. But if your hvac is not balanced and is causing negative pressure at the stove it might be dangerous even with an oak

 

[Burnhaven]

Thanks. So the air moving in and out of the stove pipe joints is coming from inside the pipe. From the small insulating air gap between the inner and outer layers? If so, where is that originating, has to start somewhere. The Hearthstone Tribute has an OAK kit installed which terminates in a 3 inch diameter opening on the back/bottom. The installer attached a metal OAK pipe to that which goes through the wall and terminates in a "dryer type" outlet, with no flapper, but with rodent screen.

 

[bholler]

I would say it is from inside the pipe but i am not there to look at it so i cant say for sure. But really other than the pipe joinst being horrible i would say that it is a hvac problem not a stove problem. But again i am not there to properly evaluate it

 

[Burnhaven]

Well back to my original thought: I would think many people do not want to shut down or close off their central furnace. Wood stove fires die out unless you plan on staying up on all night feeding it. When we lived in Northern California we did shut down the furnace when using the stove. Had single-walled interior stove pipe there. But in colder climates shutting down the furnace wouldn't be popular.
So assuming you have adequate draw and the HVAC is functioning reasonably, then you can still have times when the fire dies, the furnace is running and air gets drawn out of the DSP joints inside the living space. This seems such a likely scenario that if the two layers of the DSP weren't isolated, pipe makers would have been sued out of business long ago by relatives of dead stove users.

So I have to conclude that the real source of cool, fresh air being drawn out of the joints is outside -- either from the OAK or from up at the top of the chimney somehow.

If our furnace was drawing way too much air, or if we had too many kitchen/bath fans going, I'd have trouble getting a fire started and smoke blow back when I opened the stove door --- this only seems to be an issue here when the furnace is running AND we have other fans running.

 

[bholler]

So assuming you have adequate draw and the HVAC is functioning reasonably, then you can still have times when the fire dies, the furnace is running and air gets drawn out of the DSP joints inside the living space. This seems such a likely scenario that if the two layers of the DSP weren't isolated, pipe makers would have been sued out of business long ago by relatives of dead stove users.

No When a furnace is set up right and the stove is the proper distance from the return there is no danger of that. And the 2 layers are separate but if the joints are not together properly like in your install there is nothing the pipe manufacturer can do. And if you have negative pressure in your house there is always a danger of pulling fumes out fix the problem with the hvac and stop worrying about sealing something that does not need to be sealed Also i still have not seen where is your return vent in relation to the stove?

 

[DougA]

I'm told all interior stove pipe leaks at the joints

That is not true if they are installed correctly. You are talking about double wall and on my installation, I can hold my hand on the outside pipe 5' away from the stove. I have regularly checked my installation with my IR gun and double wall is air tight and great when installed correctly. I also have an OAK (fresh air kit) on my Hearthstone as the only source of incoming air for the stove.

On the question about stove and furnace, the other answers are correct. If both are installed and working correctly, they can co-exist without any problems. From your other post, it looks like you have a Hearthstone stove and it should have a full night's burn. However, you are in WA and you are probably burning fir, so that will not be the case. If you have access to aged hardwood, you may want to burn the fir during the day and hardwood overnight. If you can keep the fire hot, it will also eliminate your fears.

Lastly, although I am a huge supporter of CO alarms and I understand CO is odorless, in your situation, if the air is coming into the house from the gaps in your pipe, you should be smelling smoke. If you don't and if your CO detector is showing 0, I would not worry.

 

[Burnhaven]

The air return is about 25 feet away from the stove, in the same room, at the ceiling. No CO alarms, but I would like to get a meter or something that shows levels.

 

[Tenn Dave]

The air return is about 25 feet away from the stove, in the same room, at the ceiling. No CO alarms, but I would like to get a meter or something that shows levels.

You need to get CO alarms immediately Every home with a combustion appliance (furnace, hot water heater, gas stove, fireplace, wood stove, etc) needs CO detector alarms.

 

[Burnhaven]

The house was just constructed with ceiling combination CO/smoke alarms. I want to get additional CO detectors to put on a few walls, including at least one that has an LED readout of the level.

 

[Tenn Dave]

The house was just constructed with ceiling combination CO/smoke alarms. I want to get additional CO detectors to put on a few walls, including at least one that has an LED readout of the level.

Sorry, I misunderstood. I thought you did not have any CO alarms.

 

[begreen]

A properly designed forced air system is going to be pressure neutral. But most heating system are only heating one home with a single closed envelope. Our system comes on all the time when the stove is dying down. No issues whatsoever.

The seal on stove pipe is not perfect, nor does it normally need to be. Draft keeps a slight negative pressure on the pipe at all times. That is unless something artificially creates negative pressure around the pipe. This is what seems to be happening in this house when the furnace blower comes on. It is not a flaw in the pipe, it is a flaw in the hvac design. Ideally both units would have independent systems. A mini-split would probably serve the apt nicely.

 

[Burnhaven]

For now we've closed off our air return to the furnace. The other wing has two returns. Now just need to learn proper care and feeding of this soapstone stove. Never had one like this before.

 

[begreen]

If closing the apt return solves the smoke issue, you need to speak to the hvac system designer. There needs to be additional return capacity added to the main house to make up for the loss of the apt return. Otherwise the system will be unbalanced causing the blower fan to race and die prematurely.

 

[Burnhaven]

It was our hvac installer who suggested blocking our return. When pressed, he said its a variable speed fan. My son in the main wing said his supply vents are blowing a little more air than before.