Replacement air

[Tommymc]

We've been burning wood in our log home for the past 35 yrs in a 1975 Defiant wood stove. When we moved in, the house was very leaky. Through the years I've sealed air leaks, trying to tighten things up. Then a few years ago, we built an energy efficient addition and made a few improvements (insulation and new windows) to a few of the ground floor rooms. It's hard to believe the house is totally airtight, as some original doors and windows remain, but replacement air seems to have become an issue. Last winter we were plagued with back drafts and smoke in the house. Even in the non-heating months, we get a 'creosote' smell when running the kitchen or bathroom vents. Clearly, the fans are drawing replacement air through the easiest source: the chimney. Right now, we're leaving a window cracked, but in the cold months, that creates a draft and letting cold air in seems counterproductive.

I'm looking for ideas on how to both supply combustion air to the stove, and replacement air for when the vent fans are running. I can envision some sort of ducting coupled with a heat recovery system. As I understand it, heat recovery vents (HRV) supply replacement air to the entire house, but run continuously and simply exchange air 1:1. Can they make up for the air deficit caused by exhaust fans and combustion? Any help and suggestions welcome.

 

[begreen]

There are variations of HRVs and ERVs that have more or less options. Only the simplest are 1:1 exchangers. The better units can be tuned to balance the air flow. This has been covered in more detail in the Green Room and sometimes in the DIY forum. How tall is the flue system on the Defiant? Is it in the main house or addition?

 

[Tommymc]

There are variations of HRVs and ERVs that have more or less options. Only the simplest are 1:1 exchangers. The better units can be tuned to balance the air flow. This has been covered in more detail in the Green Room and sometimes in the DIY forum. How tall is the flue system on the Defiant? Is it in the main house or addition?

The Defiant is central in the original house, and close to the addition (6 ft pass-through into a great room). The stove pipe is about 3.5 feet with a 90 degree bend into the chimney. Then about 15+ ft to the top of the chimney. I'd been thinking of a floor or wall duct near the stove connected to outside air...hopefully through some sort of heat exchanger.

 

[begreen]

Is the addition taller than the main house? Can you post a picture of the chimney and rooftops of the main house in relation to the addition?

 

[Nordicbynature]

Can you find information on how much air the stove is consuming?

I have a Jötul, it uses 3.3 L/sec. It needs about 270 BTU to heat that outside air to room temperature. About 1.6% of the stoves nominal output power.

I would just open up an inlet in the wall near the stove. Close it, while not running the stove.

 

[brenndatomu]

The new addition could be causing turbulence/etc around the chimney....and it's possible (likely?) that adding 2-3' to the chimney height could help overcome the new added resistance
In the summer you could block the flue, they make "balloons" for that...in the winter a 3" air intake near the stove may help too

 

[begreen]

The new addition could be causing turbulence/etc around the chimney....and it's possible (likely?) that adding 2-3' to the chimney height could help overcome the new added resistance
In the summer you could block the flue, they make "balloons" for that...in the winter a 3" air intake near the stove may help too

Yes, before recommending fixes, I'd like to ascertain if there are exterior influences creating positive pressure around the chimney cap.

 

[Tommymc]

Thanks for your replies. The new addition is lower than the main house. For the first year or two after building it, there was no problem with the draft. The addition is a new kitchen/dining area. Last year, we converted the old kitchen into a larger bath, mudroom, and laundry. That area, which represents 1/2 of that side of the house got tightened up with new windows, entry door, and insulation.

My gut feeling is that poor draft is just one symptom of a tighter house. Even in the summer, the replacement air while running the exhaust fans is coming down the chimney. I assume that blocking the flue off in the warm months would just draw air from somewhere else...or make the vent fans work harder and be less effective. What I think I need is a unit heat recovery unit that will be responsive to inside air pressure. Begreen has mentioned that such things may exist. Any recommendations as to which ones to look at?