Chimney height in addition/wing with lower roof than main house

[nhwoods]

Hi all,
Working on designing a 20 x 24 addition with fireplace. This would be single story, with cathedral ceilings and it would be join the main house through a 12' opening. The main house is a two-story colonial. Does the chimney need to be two feet higher than the peak on the main two-story house or can it merely be two feet higher than the peak in the addition? My guess is the only way to have the shorter length is to completely seal off the addition from the main house.

 

[Corey]

I think code is generally two feet higher than anything within 10 feet of the pipe. Though we've had several people over the years complaining of poor draft in the exact situation you mention... stove in a single story add-on of a two story house. The two story house will act like its own chimney and fight for air with anything in the add on. If I had to do it, I'd be looking to get the chimney two feet taller than any portion of the house. That should at least give you a fighting chance. Hopefully others will chime in as well.

 

[gthomas785]

How far away (horizontally) will your chimney be from the main house? I have a similar setup, My chimney is about 15 feet away from the 2-story part of the house and is about 3 feet above the 1-story roof. Drafts fine. By code you have to be 3 feet tall above the roof and 2 feet above anything within 10 feet.

Edit: Your total chimney height should be a consideration as well. Most new stoves want at least 15' of rise from the stove flue collar which is sometimes not achieved in a single story setup if you just follow the 3-2-10 rule.

 

[Highbeam]

How far away (horizontally) will your chimney be from the main house? I have a similar setup, My chimney is about 15 feet away from the 2-story part of the house and is about 3 feet above the 1-story roof. Drafts fine. By code you have to be 3 feet tall above the roof and 2 feet above anything within 10 feet.

Right, the whole “higher than the ridge” thing is not a rule.

 

[nhwoods]

Thanks all! Minimum distance to the closest point of the main house would be 14'. Might be further if we slide the addition forward a little more. One more question...I have read about some having that issue mentioned above of the main house acting like a competing chimney. Do you think that affect would be greater on a 10' long by 9' high opening (free span) or a smaller opening of say 6' long x 80" (double french doors)?
Thanks again!!

 

[Corey]

IMHO - as yoda says - 'Size matters not.' You are basically building a giant "U". The stove flue is one upright and the 2-story house is the other. If the connection between the two - your doors or pass-through opening - is bigger than the stove pipe (which either is by multiple orders of magnitude) then there is effectively free-flow between the two legs of the U. All that matters then is which one drafts stronger.

Also bear in mind that "burning fine" and "easy starting" and "doesn't set off CO detectors when the fire dies down" are three completely different modes of operation. The first is easy - the second two are where problems can arise. Your actual flue will have some effect too. If you have a "mostly interior" insulated pipe, only peeking out a few feet at the top of the roof (which it sounds like, given the cathedral ceilings), that would be ideal. If you plan to go 'through the wall' and have a full exterior pipe, fully out in the cold, then you are increasing the slope of your already up-hill battle.

 

[begreen]

Thanks all! Minimum distance to the closest point of the main house would be 14'. Might be further if we slide the addition forward a little more. One more question...I have read about some having that issue mentioned above of the main house acting like a competing chimney. Do you think that affect would be greater on a 10' long by 9' high opening (free span) or a smaller opening of say 6' long x 80" (double french doors)?
Thanks again!!

Is this fireplace going to be a masonry fireplace mostly for ambiance or a modern EPA ZC fireplace for heating and fire view?

 

[nhwoods]

Is this fireplace going to be a masonry fireplace mostly for ambiance or a modern EPA ZC fireplace for heating and fire view?

This is primarily for ambiance, and at first we were mostly thinking masonry. However, as we've been looking at the ZC options, we're becoming more intrigued. Would one or the other have a better chance of performing better in our setup? Also when one is talking about an interior insulated pipe, does that include a pipe running inside and exterior wall?
Thanks again!!

 

[begreen]

A good EPA fireplace will actually heat the place, like a wood stove would. A basic masonry fireplace will radiate heat, then suck it all back up the chimney as the fire dies down. Glass doors can help reduce the losses.