Wood Stove vs. Tight House

[MikewhoisfromMaine]

Hi all,
We have a Morso 3450 heating a very tight 1700sf house, which wasn't originally intended to be heated by wood, but I was doing tree work so got free wood, I had to do it. The ventilation was designed to be done with exhaust fans, however, the stove is now by far the largest hole in the house. When the stove is not running, which is often because there is plenty of passive solar so any reasonably sunny day there is no need, any fan such as a bathroom fan, dryer, or stove hood pulls ash smell into the house and can give us sore throats if it's bad. When it is burning it works as its own "fan" fairly well.

We crack windows when using fans, and that seems to be the simplest solution, but I've been wondering if there is another way. One idea was to put a draft inducer fan in the chimney, but the style that seems like it would be more effective(on top of chimney) has to be running whenever the stove is running and that seems both lame and has the potential to overheat the stove. The upside would be that you could ventilate the house to your hearts content without any ash in the house.

My next idea is to be able to close the chimney when it's not in use. Maybe a damper would help, but it's not airtight(neither is the stove, but I had made an assumption that modern stoves were), so some airtight damper might help. I don't know.

Note: it has an outside air supply, but I think it's both unnecessary(it get enough air from the house), and detrimental as it, I think, replaces the air that would otherwise be going into the open door when I reload it, so smoke is more likely to spill out.

Any thoughts?

 

[stoveguy2esw]

if the OAK were not there you would have even more issues with the negative pressure buildup the fans and such which pull air from the house could overpower the flue even with the stove running without the OAK

 

[jdonna]

Where is the stove located in relationship to your house? Basement, main level, split level ect. How tall is your chimney? What is the size of the chimney?

I think some more info is needed so people can give you some suggestions. Sometimes with complicated problems its good to get a professional for advice or take a look at things.

 

[Cynnergy]

Note: it has an outside air supply, but I think it's both unnecessary(it get enough air from the house), and detrimental as it, I think, replaces the air that would otherwise be going into the open door when I reload it, so smoke is more likely to spill out.

Does this mean that your stove has the ability to have an OAK, but you haven't installed one? Most people here recommend an OAK for tight houses, but here's some additional reading if you want more info: http://woodheat.org/the-outdoor-air-myth-exposed.html

I have copied and pasted the second to last paragraph for info:

'The main disadvantage of taking air from inside the house is that the pressure environment can be adversely affected by powered exhausts. However, depressurization caused by powered exhaust flows is predictable and manageable, unlike the more random and unpredictable effects of wind on outdoor air supplies. The worst-case indoor air pressure environment can be measured using the house pressure test procedure, and can be controlled either by limiting exhaust flows or by installing a powered make-up air system.'

I believe if you don't have or don't want an OAK, your best bet would be to install a make-up air system (something like a fan linked to your major exhausting appliances that will turn on when they're on). And be careful trying to light the stove if you have any other fans on - if you are getting ash in the house it sounds like your flu is reversing and that can lead to a lot of smoke in the house! AFAIK, smoke spillage on reloads tends to be from opening the door too fast or else poor draft - I don't think an OAK will affect it, but I have no experience with this.

 

[Oregon aloha]

Would a barometric damper help? I know it helps a wood stove get more air in a tight house that doesn't have an OAK. It only opens to bring air into the house when the needed.

 

[brenndatomu]

Either your chimney or your outside air supply(OAK) or both, is inadequate. Stove guy is correct, if you didn't have the OAK, things would be worse!

 

[MikewhoisfromMaine]

Thanks for all the replies everyone!

It is on the first floor of a two story house built on a slab, so no basement. The 6" pipe goes up and out to an external insulated metal chimney that goes up to the peak, 25' I'd guess.

Starting and running the stove is no problem, although I do have to crack a door for a couple of moments to get it ready to light, but no big deal. The problem is that the stove is a hole, and the oak is neither here nor there it seems to me, in fact, I've but a bag over the fixture outside for it and I do think it helps with the loading. Either way, since the stove is not airtight, air comes in through it when a fan is on and it's not burning hot. Now, I don't think the oak is of the "proximity" variety, which is like an open window near the stove(we do have one which I use to great effect when it's running and a fan is on). So, whether its coming in from the oak and through the stove or down the chimney and through the stove, it doesn't matter. I think the oak is a distraction in this case because the problem is happening when there is no fire.

A make-up air system would be great, but it's too expensive and invasive for this house. With the solar pv and thermal systems it is already fairly costly for its size, I don't think more investment would work.

People are building more and more tight houses, and wood heat isn't going away, so it seems like an opportunity to figure out a system that works. In my view, the ability to actually open and close the system would be the ticket, no?

 

[KaptJaq]

As you have already noticed modern "airtight" stoves aren't. The OAK & flue appear to be adequate since they function properly when the stove is burning. Your main problem is when the stove is not burning. Pressure in the house drops due to an exhaust fan, (Kitchen, bath, clothes dryer, etc). The house is tight enough and the pressure is trying to equalize. The easiest path is via those EPA required, always open, air vents on your stove. Outside air can come in via the OAK or flue, through the stove where it picks up some particulate, then into the house via the vents.

IMO there are two solutions:

1. If you can find the vent holes on your stove then cover them when the stove is not in use. (Magnets, foil tape, etc...) Sometimes easier said than done. Some stoves the inlet is an obvious hole on the back or bottom. On mine the inlet is hidden behind the surround and within the fan's air chamber.

2. Put closing caps on both the OAK and the flue. When the stove is not in use, seal the air paths. If air cannot be pulled into the stove it will not come into the house. Just make sure the control for the flue cap is visible when starting the stove. Forgetting it once will put more smoke in the house than is currently drawn via the stove all week.

KaptJaq

 

[stoveguy2esw]

Would a barometric damper help? I know it helps a wood stove get more air in a tight house that doesn't have an OAK. It only opens to bring air into the house when the needed.

not with an epa stove, this could cool your chimney temps by robbing combustion air from the stove. I would never want a barometric in a modern woodstove's flue system, the stack temps are critical to performance so letting in room temp air could be a real problem with a stove designed this way as the flue temps are naturally lower in the chimney when attached to this type stove compared to the old non epa units. they simply do not waste as much volume of heat out the flue.

 

[MikewhoisfromMaine]

1. If you can find the vent holes on your stove then cover them when the stove is not in use. (Magnets, foil tape, etc...) Sometimes easier said than done. Some stoves the inlet is an obvious hole on the back or bottom. On mine the inlet is hidden behind the surround and within the fan's air chamber. 2. Put closing caps on both the OAK and the flue. When the stove is not in use, seal the air paths. If air cannot be pulled into the stove it will not come into the house. Just make sure the control for the flue cap is visible when starting the stove. Forgetting it once will put more smoke in the house than is currently drawn via the stove all week.

Yes! That is what I'm talking about. Option 1 is hard since everything is fairly hidden behind plates and whatnot. Option 2: what would you install? I can't find anything besides a damper that isn't airtight.....

 

[KaptJaq]

There are a bunch of chimney top sealers out there, the first two google returned are:

http://www.woodlanddirect.com/Chimney/Top-Sealing-Chimney-Dampers/Seal-Tight-Chimney-Top-Damper

http://www.woodlanddirect.com/Chimn...ers/Chim-A-Lator-Top-Sealing-Chimney-Damper_2

For the OAK it will be a little harder. For one install we put a 4" gate valve with two 4" nipples and clamped the flexible OAK line to the nipples. Hard mounted the gate valve behind the surround and extended the handle through a vent in the surround. Painted the handle black and it was hardly noticeable.

Your install will dictate what can be done.

KaptJaq

 

[MikewhoisfromMaine]

I spoke too soon about option 1. Found the hole, foil taped it. Turned on fan.......No smell! Now we have to remember to adjust where the dial goes for low burning, but we can do it. Just a little annoyed at how simple it was. Thanks!

 

[KaptJaq]

Simple is usually best. I like the magnet idea, easy to remove when you want to use the inlet, easy to seal when you don't need the inlet.

Enjoy your stove...

KaptJaq

 

[MikewhoisfromMaine]

I liked the magnet too, but it's all behind two separate plates, one of which has many bolts. That and I don't have a magnet like that.

However, I've since realized something potentially interesting:

When I put the bag over the oak, I assumed without thinking that there were multiple air intakes, otherwise the fire would die. This is why I didn't think to do option 1 because it seemed hard to track them all down. But, the oak led to an airtight chamber with a permanent hole(now closed), and an adjustable hole. They had the "air" of being there for a reason, like the only ones. See what I did there? Anyway, When I did my fan test, it SEEMED to me that smoke wasn't coming out of the stove. In addition, and importantly A TRICKLE OF AIR WAS COMING IN THROUGH THE NOW DISMANTLED OAK, AND I MEAN A TRICKLE. If there was no air, the fires of the last week would have died, or there were more holes in the stove that what the oak led to. THE PERCEPTION THAT THE STOVE IS RELATIVELY AIRTIGHT NOW, ALONG WITH THE FACT THAT THERE WAS A TRICKLE, MAKES ME THINK THE FIRE WAS RUNNING OFF THAT TRICKLE. THAT OAK HAD A PLASTIC BAG OVER IT! OK, of course is an imperfectly sealed bag, with maybe a hole in it, otherwise air wouldn't be coming in with the fans on, but the implication for oaks in general is that the stove doesn't need any more air than what even the tightest house can provide.

I have to verify somehow that it is in fact airtight, maybe lack of issues over long term may work for me. I could try to squelch a fire but that seems smoky to me.

 

[MikewhoisfromMaine]

Update: I had a nice fire going, and I then shut off the air, but I could hear a whistling noise as if air was still coming in. Sure enough, the fire didn't die, so the stove is still not airtight, and particulates and smoke smell still enter the house when the exhaust fans are running and there is no fire. BUT, I did try a party balloon in the cleaning port in the metal chimney outside, and that seems to do it. I'm going to order a custom sized chimney balloon from here.

 

[DougA]

I also have an air tight house,(pressure tested) with enormous south windows for passive solar plus a slab floor for thermal mass. Sound similar? I also have a wood stove that has been working great (although undersized) for 30 years. Your problem is that you don't understand the dynamics of air pressure and you are working against physics, something that you can't win.

With your size of house, you absolutely must have an air exchanger. Living without one is very unhealthy in an air tight house. I can't believe any building code would allow it. If you need to crack a window to use the exhaust fan on your kitchen stove, you have problems big time. A passive air exchanger is inexpensive and pretty easy to install yourself. The stove is the least of your problems. Moisture from everyday living will be getting into your insulation and you will soon have mold in your structure. OAK is very important for the proper operation of a wood stove in an air tight house. The air has to come from somewhere, without OAK it will either find it's way through cracks or your fire will not burn correctly. You may even have a CO (Carbon Monoxide) problem and not even know it. In our area, CO monitors are mandatory if you have any combustion device.

When your stove is cold and closed off with the normal controls, it should present no problem with ash smell coming into the house when you turn on an exhaust fan in the kitchen or bathroom.