Exhaust Fans and Negative Pressure

[BuckyBeaver]

Hi Folks. I have a question regarding kitchen and bathroom exhaust fans. Will using them cause negative pressure problems for a woodstove's chimney draft? Thanks in advance for your input.

 

[begreen]

It depends on the house and the location of the stove. If the home is very tightly sealed, then exhaust fans can affect stove performance. Kitchen exhaust fans tend to be more powerful and their effect more noticeable. If the stove is in the basement it can be more vulnerable to negative pressure.

 

[Iembalm4aLiving]

If I try to start a fire when the kitchen fan is on, I'll get smoke pouring into the room. Once the fire is started and a good draft is going, the fan doesn't affect the stove. YMMV.

 

[BuckyBeaver]

It depends on the house and the location of the stove. If the home is very tightly sealed, then exhaust fans can affect stove performance. Kitchen exhaust fans tend to be more powerful and their effect more noticeable. If the stove is in the basement it can be more vulnerable to negative pressure.

thanks begreen

 

[BuckyBeaver]

If I try to start a fire when the kitchen fan is on, I'll get smoke pouring into the room. Once the fire is started and a good draft is going, the fan doesn't affect the stove. YMMV.

thanks gd9704

 

[fox9988]

Bath exhaust fan makes a noticeable difference in my draft, but the dryer really kills it.

 

[BuckyBeaver]

Bath exhaust fan makes a noticeable difference in my draft, but the dryer really kills it.

How do you handle that problem, especially the dryer??

 

[BuckyBeaver]

How do you handle that problem, especially the dryer??

Can you just open a window in the room of the dryer to equalize the pressure?

 

[begreen]

Yes, or add an OAK (outside air kit) to the stove.

 

[DexterDay]

Yes, or add an OAK (outside air kit) to the stove.

X2..
An OAK makes the stove more efficient and a completely sealed system. No fans or other air movers will affect your draft and you wont suck cold air in all the leaky and drafty points in your house, to make up for the air that goes up your flue. Every cu ft of air that goes up your chimney, has to be replaced with Cold air that infiltrates all the drafts in your house. An OAK will stop all of that.
Opening a window allows cold air in your home. An OAK only allows that air to be used for combustion. If your stove has an OAK inlet on it?

What stove do you have?

 

[BuckyBeaver]

X2..
An OAK makes the stove more efficient and a completely sealed system. No fans or other air movers will affect your draft and you wont suck cold air in all the leaky and drafty points in your house, to make up for the air that goes up your flue. Every cu ft of air that goes up your chimney, has to be replaced with Cold air that infiltrates all the drafts in your house. An OAK will stop all of that.
Opening a window allows cold air in your home. An OAK only allows that air to be used for combustion. If your stove has an OAK inlet on it?

What stove do you have?

Woodstock Progress Hybrid

 

[DexterDay]

Woodstock Progress Hybrid

Yes it has an OAK inlet and Yes it will improve the overall efficiency. Along with eliminating the fear of having draft issues because of other air movers.

 

[fox9988]

Can you just open a window in the room of the dryer to equalize the pressure?

Yes, I crack the bathroom window.

 

[BuckyBeaver]

Yes it has an OAK inlet and Yes it will improve the overall efficiency. Along with eliminating the fear of having draft issues because of other air movers.

Thanks for the info

 

[BuckyBeaver]

Yes, I crack the bathroom window.

thanks

 

[DickRussell]

If the house is tight, then even with an OAK installed you can have problems when lighting the stove if the range hood or dryer is on. Then you can just open a window near the stove while lighting it off. Once a good draft up the chimney is established, you can close the door to the stove and shut the window. Either that or turn off the range hood or dryer until you get the stove going. This is my experience with our new house, which is quite tight. Our stove does have an OAK.

 

[Ashful]

Careful with those OAK's. If the inlet is on the leaward side of the house on a windy day, it can actually cause reverse draft.

I've seen more than one engineer recommend providing make-up air at the source of the exhaust (near kitchen range, near dryer, etc.), rather than using an OAK.

Here's one very good discussion on the subject: http://woodheat.org/the-outdoor-air-myth-exposed.html

 

[BuckyBeaver]

If the house is tight, then even with an OAK installed you can have problems when lighting the stove if the range hood or dryer is on. Then you can just open a window near the stove while lighting it off. Once a good draft up the chimney is established, you can close the door to the stove and shut the window. Either that or turn off the range hood or dryer until you get the stove going. This is my experience with our new house, which is quite tight. Our stove does have an OAK.

thanks dick

 

[BuckyBeaver]

Careful with those OAK's. If the inlet is on the leaward side of the house on a windy day, it can actually cause reverse draft.

I've seen more than one engineer recommend providing make-up air at the source of the exhaust (near kitchen range, near dryer, etc.), rather than using an OAK.

Here's one very good discussion on the subject: http://woodheat.org/the-outdoor-air-myth-exposed.html

very interesting Joful.

 

[blwncrewchief]

Careful with those OAK's. If the inlet is on the leaward side of the house on a windy day, it can actually cause reverse draft.

I've seen more than one engineer recommend providing make-up air at the source of the exhaust (near kitchen range, near dryer, etc.), rather than using an OAK.

Here's one very good discussion on the subject: http://woodheat.org/the-outdoor-air-myth-exposed.html

While I will not totally disagree with the woodheat.org article do take it with a large grain of salt. It is an opinion that is only one side of a ten sided puzzle. Giving a blanket statement about what is best for all situations is just not possible in reality. There are dozens of potential issues with natural draft appliances and quite frankly 90% of the buildings out there are not designed "properly" for the given ventilation potential in the building. I have had to deal with hundreds of buildings with draft reversal problems over the years and not one has had to do with an "OAK". All of them have been from either depressurization issues or a very few from design problems. My opinion from 20+ years of HVAC design engineering would be you are 99 more times likely to have a draft reversal event with a natural drafting appliance without an "OAK". Now the potential is there for the case of circumstances stated in the article and why I said I did not totally disagree with the article. It is NOT an exacting science because of all the potential problems that come into play. I usually keep my mouth shut when I see this argument because it is a non winnable fight. There is not a perfect answer because every situation is different. Be aware of anyone claiming to be able to give a definitive one answer blanket statement on this type of issue. I will only give an opinion and that is my stove has an OAK.
.

 

[peakbagger]

If the house is tight enough to see a difference in draft, with a bathroom fan on, its time to consider and air to air heat exchanger. These units are code in most new energy efficient homes and in addtion to swapping stale air in the house, they balance the pressure. I have a friend that did a major renovation and spray all the walls with foam and had really good windows, when you close the door from outside you can feel the windows bow out.With the heat exchanger he has a pellet stove and wood stove with a failry short chimney with few issues

 

[John_M]

Bucky, here are two links you might find helpful: http://www.chimneysweeponline.com/hodraft.htm and http://www.chimneysweeponline.com/hooa.htm

There are many other helpful links on the chimney sweep web site.

Good luck!

 

[BuckyBeaver]

Bucky, here are two links you might find helpful: http://www.chimneysweeponline.com/hodraft.htm and http://www.chimneysweeponline.com/hooa.htm

There are many other helpful links on the chimney sweep web site.

Good luck!

thanks John

 

[BuckyBeaver]

If the house is tight enough to see a difference in draft, with a bathroom fan on, its time to consider and air to air heat exchanger. These units are code in most new energy efficient homes and in addtion to swapping stale air in the house, they balance the pressure. I have a friend that did a major renovation and spray all the walls with foam and had really good windows, when you close the door from outside you can feel the windows bow out.With the heat exchanger he has a pellet stove and wood stove with a failry short chimney with few issues

thanks