Tight house, range hood, and a BK Princess Ultra...

[bwooten]

Hi everybody! Kind of a story here, and kind of a question... My wife and I are renovating/adding on to our small house. We are mid-stream as regards the whole process, but part of the upsizing involved replacing our old small wood stove with a wonderful Blaze King Princess Ultra. This is our primary heat source.

We LOVE this stove. Can't say enough good things about it.

The new building envelope, windows, and doors, however, make for a very tight house... in Winter, very little air gets in or out except by way of the HRV. Yesterday we installed our range hood - hooray, cooking! This hood has four airflow settings: 400cfm at its lowest, 1000cfm at its highest.

This evening we turned on the hood while boiling water for tea, just to test it out. Almost immediately, the Princess' fire squelched out and it started to belch smoke out its backside. After a moment of panic - worried a chimney fire may have started - we realized the HRV was off. No make-up air was being introduced to replace the air being pulled out by the range hood, and presto... Smaug the Terrible is alive in our living room.

We turned off the hood and opened a window, then we turned on the HRV to a medium setting. The Princess sprang back to life immediately, nice draft established, flames jumping etc.

With the HRV running, we closed the window, and turned the range hood back on.

Smaug!

We reopened the window, turned the HRV to maximum, closed the window once more and tried the hood again.

Smaug!

We tried many variations on the same theme - stove on its lowest and highest thermostat settings, HRV high/low etc. - it always ended with an open window to avoid the negative pressure.

Apparently, we are not able to run the stove and range hood at the same time, unless we have a window open, which is a frosty proposal in late-February.

Have any of you experienced a similar conundrum? Do you just open the window while the hood runs and live with it in the winter months, or has anybody found any ingenious solutions to this problem?

 

[westkywood]

Hi everybody! Kind of a story here, and kind of a question... My wife and I are renovating/adding on to our small house. We are mid-stream as regards the whole process, but part of the upsizing involved replacing our old small wood stove with a wonderful Blaze King Princess Ultra. This is our primary heat source.

We LOVE this stove. Can't say enough good things about it.

The new building envelope, windows, and doors, however, make for a very tight house... in Winter, very little air gets in or out except by way of the HRV. Yesterday we installed our range hood - hooray, cooking! This hood has four airflow settings: 400cfm at its lowest, 1000cfm at its highest.

This evening we turned on the hood while boiling water for tea, just to test it out. Almost immediately, the Princess' fire squelched out and it started to belch smoke out its backside. After a moment of panic - worried a chimney fire may have started - we realized the HRV was off. No make-up air was being introduced to replace the air being pulled out by the range hood, and presto... Smaug the Terrible is alive in our living room.

We turned off the hood and opened a window, then we turned on the HRV to a medium setting. The Princess sprang back to life immediately, nice draft established, flames jumping etc.

With the HRV running, we closed the window, and turned the range hood back on.

Smaug!

We reopened the window, turned the HRV to maximum, closed the window once more and tried the hood again.

Smaug!

We tried many variations on the same theme - stove on its lowest and highest thermostat settings, HRV high/low etc. - it always ended with an open window to avoid the negative pressure.

Apparently, we are not able to run the stove and range hood at the same time, unless we have a window open, which is a frosty proposal in late-February.

Have any of you experienced a similar conundrum? Do you just open the window while the hood runs and live with it in the winter months, or has anybody found any ingenious solutions to this problem?

Sounds like you need to install on OAK (outside air kit)

 

[Boiler74]

I just saw a Hometime episode where they installed a range hood. Part of that install was a make up air blower with electric heater built in. It was slaved to the range good and matched to make up air as needed.

 

[edyit]

as westkywood said it sounds like an OAK is your simplest solution

 

[begreen]

What size is the range hood? Some range hoods exhaust at 600-1000cfm. That is a lot of make up air. Adding an OAK on the stove should help.

 

[Boiler74]

I am not a stove professional but I have been dealing with negative house pressure issues at my own house for a while. An OAK is designed to help the stove run in a tight house by providing IT with makeup air. This issue is being caused by a hood sucking massive amounts of air out of the house. If the house is really tight, that negative pressure could fight against the stove draft and still draw smoke and smell out of it, even with the OAK. I think the range hood is going to need makeup air no matter what. 1000 cfm is a lot. I don't think the HRV will provide that because it is balanced to exhaust the same amount of air as it brings in. Maybe there is a system that can make it only supply air and shut off the exhaust while the hood is in use. I don't know. I just don't think an OAK will fix this problem on it's own.

 

[begreen]

Yes, that is why I am wondering the model range hood. Many have a variable speed motor. A compromise solution may be an OAK and running the hood on low speed.

 

[Highbeam]

Have any of you experienced a similar conundrum? Do you just open the window while the hood runs and live with it in the winter months, or has anybody found any ingenious solutions to this problem?

Ha! Ingenious? No, but obvious? Yes. This is why you should have an OAK attached to the stove as in the pic. There are several other reasons for directly providing your stove limitless outside air for combustion but you found a big one.

It's not entirely the fault of your high CFM hood, it is your tight house. Good job. If I am starting a fire with the loading door is open, and the wife runs the cheezy range hood that is part of the built in microwave (low CFM) it will suck smoke right out into my face. Shut that thing off and smoke goes up like it is supposed to. Shut the stove door and the OAK provides the air so she can run the range hood all she wants.

This very negative pressure situation in your home would be sucking nasty chimney air into your home through the stove even when there is no fire in the summer.

Do you have any other flues? Like natural draft water heaters, furnace, etc. Those chimneys could be backdrafting as well and the CO could be deadly. If you were also running the clothes dryer and maybe a few bathroom fans you could dang near suck your ear drums out!

 

[Mike M.]

Do you have an attached garage? If you do maybe open that door instead of the window. Likely it's not as cold as outside. I'll also comment on the OAK. I had thought these were much more air tight, then I got one and wow, not tight at all. They leak a great deal when connecting to the stove. Mine leaks out the damper lever area pretty bad. That said like others stated don't really on the OAK to solve the problem.

 

[DickRussell]

.... I'll also comment on the OAK. I had thought these were much more air tight, then I got one and wow, not tight at all. They leak a great deal when connecting to the stove. Mine leaks out the damper lever area pretty bad. That said like others stated don't really on the OAK to solve the problem.

While the duct from my OAK to the stove connection is essentially tight, the air control mechanism itself isn't. If our range hood or dryer, neither of which is anywhere near the OP's lowest 400 cfm, is running when I go to light off the stove, I get backdrafting, and leakage out around the air control area even if I close the stove door right away. And this is with the HRV always running, too, which normally would go out of balance to provide net makeup air for the house when the dryer or range hood needs it. I have to open a window quickly to compensate for the backdrafting, go up and shut off whichever exhausting device is running (or just wait until "the boss" is done up there), then get the stove going. Once running with a good draft going, the exhausting devices can be run. While I haven't tried running the range hood at highest speed while the stove is running, I suspect I could do so because of having the OAK and HRV. In a tight house without an OAK, I don't see how the OP ever will have that big honking range hood and woodstove going at the same time without a window open.

The OP ought to go to greenbuildingadvisor.com and do a search on "range hood makeup air." From the list of links that gives you, this is a good start for reading: http://www.greenbuildingadvisor.com/blogs/dept/musings/makeup-air-range-hoods. Another reports on a fairly recent announcement of a makeup air kit for that oversized range hood: http://www.greenbuildingadvisor.com...ws/fantech-develops-kit-range-hood-makeup-air. Having both an OAK for the woodstove and a makeup air supply for the range hood might be appropriate. Another option is to change out that range hood for one with a lower range of speeds, one that won't risk sucking out pets and small children with the cooking odors when it's run full tilt.

 

[Highbeam]

Do you have an attached garage? If you do maybe open that door instead of the window. Likely it's not as cold as outside. I'll also comment on the OAK. I had thought these were much more air tight, then I got one and wow, not tight at all. They leak a great deal when connecting to the stove. Mine leaks out the damper lever area pretty bad. That said like others stated don't really on the OAK to solve the problem.

Depends greatly on the stove. I also own an NC30 and using an OAK for that is a huge waste of time. Only one of the four air inlets to that stove is fed by the OAK hookup. My current stove, same as the OP's, draws 100% of it's air from the OAK connection. It's not watertight but very good. My previous stove was a Hearthstone heritage that also took 100% of combustion air through the OAK snout.

 

[bwooten]

Thanks everybody for the thoughtful comments regarding this issue.

Yes, the range hood is a variable speed model: Victory Tofion 36" (http://www.kitchenhoods.ca/shop/victory-tofion-36-wall-range-hood-36.html). It has 4 speed settings, 400/600/800/1000cfm. It is vented by an 8" pipe, and in our case that pipe runs in a straight shot (no bends/turns) directly through the 6" exterior wall to the out-of-doors. So when it's operating, it does so very efficiently.

We have run the dryer, microwave etc. with the Princess ablaze and have not had any problems. Our HRV has ports in multiple locations in the house, and also runs the two bathroom fans. We regularly run that system at its highest setting, with the stove on, without backdraft issues. The only other time we've gotten backdrafting is on extremely windy days, and we do get those here on occasion (we're on a bay in Nova Scotia).

The OAK sounds like it could be part of a solution, however our wood stove sits in the middle of an open room on the concrete floor, approachable from four sides. I would prefer to avoid running another pipe through the space, if possible, but if necessary does the air supply have to be drawn from below stove-level? Or could a pipe run vertically, parallel the chimney pipe, and then t-off partway up and travel horizontally to poke out the wall? I have heard some unpleasant stories about OAKs installed in high-wind areas and/or the wrong side of a house in a high-wind area. I am concerned I might invite more problems than I already have, because when it gets windy on this hill, it swirls around like a dervish. There isn't a "less windy" side of the house... it's all pretty wild.

I'm feeling particularly bummed about this because I was careful to get a fan that could run at a 400cfm setting, precisely because I believed that was the threshold whereafter make-up air during the winter heating months becomes an issue. Seems I've really undershot my mark here.

I will contact the range hood manufacturer to see what options they recommend. They have been wonderful on the customer service end of things, so perhaps they will have a solution on how to adapt the Tofion to have make-up air delivered directly to the hood?

Thanks again for all of your comments.

::edit:: They do not have make-up air kits, and returning the hood is no longer an option as it has been hardwired and mounted already.

 

[Highbeam]

The OAK sounds like it could be part of a solution, however our wood stove sits in the middle of an open room on the concrete floor, approachable from four sides. I would prefer to avoid running another pipe through the space, if possible, but if necessary does the air supply have to be drawn from below stove-level? Or could a pipe run vertically, parallel the chimney pipe, and then t-off partway up and travel horizontally to poke out the wall? I have heard some unpleasant stories about OAKs installed in high-wind areas and/or the wrong side of a house in a high-wind area. I am concerned I might invite more problems than I already have, because when it gets windy on this hill, it swirls around like a dervish.

The rumors you heard about wind causing issues with an OAK are myths, urban legends. However, a stove in the middle of a room on a slab makes it very very hard to utilize outside combustion air. According to BK, it does have to be drawn from below firebox level much to the horror of folks in basements who are somehow able to make it work. The worry is that the OAK intake will become an attractive chimney to the smoke and so the smoke will reverse direction from normal operation.

 

[bwooten]

The rumors you heard about wind causing issues with an OAK are myths, urban legends. However, a stove in the middle of a room on a slab makes it very very hard to utilize outside combustion air. According to BK, it does have to be drawn from below firebox level much to the horror of folks in basements who are somehow able to make it work. The worry is that the OAK intake will become an attractive chimney to the smoke and so the smoke will reverse direction from normal operation.

That last part was precisely my concern... and we have no crawlspace or basement to delve into here, either. In fact, the stove sits in a little sunken living space that would put the pipe about 18" underground if it made it outside. Ugh. The above GBA links were great to read, too, about the make-up air systems. I got a screaming deal on the range hood, but $1800-$3000 for a purpose-built makeup system, that would just pull in cold outdoor air into the house anyway, doesn't make much sense to me at this point.

Opening the kitchen window just adjacent to the range in the winter seems to be the simplest, most affordable, and direct solution here? It would only need to be open when running the hood fan, which isn't a big part of each day. The draft pulled in through the window should mostly get sucked right up the hood... hopefully the cold air won't be too much of an overall heat loss, all things considered.

I would have loved to get a 36" wide fan that operated at much lower speeds (100-250cfm max) but this was the model we could get where the fan motor could be turned for a horizontal exhaust, vertical exhaust being an impossibility in our particular installation situation.

 

[3650]

I would just put the OAK in and be done with it. Follow the manufacture's install. If they want it going down below the stove (which is how my stove maker recommends) put a hole in the floor, run pipe along the floor joists, through the foundation and up. It has to terminate outside and high enough that snow won't drift over it. My stove maker sells an OAK adapter. I would imagine BK does too. If you are worried about smoke following that path put a check in the line. Just a simple swinging flap that will only open one way. They probably sell them. It'll allow air in but not out. Or you can just open a window...lol.

 

[Heftiger]

Somewhere else on this forum I read about somebody putting in a pipe through the wall where on this inside the pipe pointed up, on the outside it pointed down. Since cold air sinks there should be no flow through the pipe unless there was negative pressure in the house. Not sure if that's common or if it worked, but it seemed like a simple solution.

 

[Highbeam]

I would just put the OAK in and be done with it. Follow the manufacture's install. If they want it going down below the stove (which is how my stove maker recommends) put a hole in the floor, run pipe along the floor joists, through the foundation and up. It has to terminate outside and high enough that snow won't drift over it. My stove maker sells an OAK adapter. I would imagine BK does too. If you are worried about smoke following that path put a check in the line. Just a simple swinging flap that will only open one way. They probably sell them. It'll allow air in but not out. Or you can just open a window...lol.

It's on a slab so they would have to cut concrete and then trench in the dirt. I am pro OAK but not in this situation, way too hard.

 

[Beerdog]

Hi bwooten...
We have a similar situation with our new home. Tight home, 400+ CFM range hood, woodstove in the basement with and OAK. We heat with a propane fired boiler that has it's own dedicated air supply to the same general area occupied by the wood stove. To provide the required air exchanges we run two 50 CFM bathroom fans continuously.

Some additional background:
The size of a range hood is stipulated by code and related to the Btu output of the range. Code will require a hood sized to the range, and recent code changes require makeup air if the hood exceeds 400 CFM.

Our OAK does not directly feed into the stove, and I am not sure any do. I read some where that stoves must also draw air from their surrounding space and not rely totally on a sealed OAK as its sole air source. Perhaps someone in the industry can clarify here. Anyway, the air plenum feeding my stove's combustion chamber is open to the room air, the OAK dumps into that plenum. So, a pressure drop in the home is experienced by the stove since. The OAK will help reduce the pressure drop, but it is insufficient with my stove.

When we run our range hood at its lowest setting, the barometric pressure in the home drops and we get a negative draft.

I solve the draft problem by coordinating wood stove and hood use, and by opening a window a couple of inches in the area where the stove is located. Not ideal, but it works.

Since our home was built two years ago, the code changed and it now requires builders take makeup air into consideration. I was aware that the hood would be an issue and installed a wall switch to electrically activate a damper in a 6" duct which I have yet to install into the basement's exterior wall. When we built the home three years ago, no residential range hood manufacturer was addressing the issue with a commercially available solution to provide make-up air. I spoke with high end range hood retailers, installers and contractors and they generally had a glazed look in their eyes when I raised the issue. Not a clue.

Your HRV won't be any help here because it's designed to balance exhaust and intake air flows. Conceptually, a HRV has two fans operating at the same flow rate... one exhausting and one blowing in. They are designed to balance the air going through the HRV... not to accommodate flow imbalances caused by other sources.

Some possible solutions:

Put in a damper in a duct between the conditioned space and the outside to balance the air pressure. It would allow outside air to enter the home when the home's pressure falls below the outside air pressure and allow pressures to equalize. A barometric damper is automatic and non-electrical solution. An electrically controlled damper in a duct between the inside and outside could be switched or tied into the range hood fan's power. I looked into tying the damper's operation with the fan, but I was afraid that any work I did might void the range hood warranties and cause problems passing the electrical inspection.

To equalize pressure, open a window. Not elegant, poor air control, defeats the energy efficiency measures you've got, and creates drafts. Also easily forgotten to close. I killed an African violet that way. Froze it to a crackely crunch. Wife was not pleased.

If your home is heated with a furnace, you may have an outside air supply tied into the system with dampers that could be opened or closed.

Bottom line is that the range hood reduces the home's air pressure below the outside air pressure. You can only overcome that by allowing air to enter the home.

John

 

[bwooten]

These are all good points, and thanks for relaying your situation/solutions.

Our stove is the primary heat source. We have in-floor heat, too, but seldom run it as the Princess does such a good job and the electrical system for the floor heat can be expensive.

400cfm is the make-up air threshold (code-wise) where we live in Canada, too. The damper-in-a-duct seems like a good solution, and basically amounts to opening a window without having to worry about closing it, yes? I am sorry to hear about your violet. Have you been forgiven yet?

I have written to the range hood company to see if our installing a rheostat would solve the problem? We really only need 150-200cfm, so if we could control the current in the winter heating months and keep it at that range, then maybe it would suffice to prevent backdrafting and we could keep our windows closed. Hopefully the motor can take kindly to infinite current adjustment?

In the meantime, we crack open the kitchen window during use, and it really pulls (I put my face in front of it last night and it made my hair shoot straight up). The cold air mostly seems to go right up the range hood and out again. It doesn't seem to cool the rest of the house off noticeably, as long as it is not left open after the hood is off. A stop-gap for now, or maybe the permanent solution if the rheostat doesn't pan out.

 

[Highbeam]

These are all good points, and thanks for relaying your situation/solutions.

Our stove is the primary heat source. We have in-floor heat, too, but seldom run it as the Princess does such a good job and the electrical system for the floor heat can be expensive.

400cfm is the make-up air threshold (code-wise) where we live in Canada, too. The damper-in-a-duct seems like a good solution, and basically amounts to opening a window without having to worry about closing it, yes? I am sorry to hear about your violet. Have you been forgiven yet?

I have written to the range hood company to see if our installing a rheostat would solve the problem? We really only need 150-200cfm, so if we could control the current in the winter heating months and keep it at that range, then maybe it would suffice to prevent backdrafting and we could keep our windows closed. Hopefully the motor can take kindly to infinite current adjustment?

In the meantime, we crack open the kitchen window during use, and it really pulls (I put my face in front of it last night and it made my hair shoot straight up). The cold air mostly seems to go right up the range hood and out again. It doesn't seem to cool the rest of the house off noticeably, as long as it is not left open after the hood is off. A stop-gap for now, or maybe the permanent solution if the rheostat doesn't pan out.

Funny thing about centrifugal motors is that they are not positive displacement pumps. You can just restrict the outlet to reduce the flow rate. Power consumption drops since the blower isn't actually doing as much work so you will probably hear the motor spin up slightly. When you've got them on the phone, ask if you can restrict the intake or outlet.

 

[begreen]

It's on a slab so they would have to cut concrete and then trench in the dirt. I am pro OAK but not in this situation, way too hard.

In this case could the OAK can go directly out the wall behind the stove?

 

[Heftiger]

Can we get a picture of your install?

 

[Highbeam]

In this case could the OAK can go directly out the wall behind the stove?

In a sunken living room I assumed the stove is not on an outside wall.

 

[showrguy]

In a sunken living room I assumed the stove is not on an outside wall.

Since it's allready in a sunken room, why not un-sink it by 4-6 inches ??
Frame it up, run OAK, insulate, sheet, hearth, flooring, done !

 

[begreen]

Yes, I need a better visualization of the setup.