[Greenbuilding] Visible Flames (Fireplaces) in Tight Houses

[Norbert Senf]

On Wed, Dec 3, 2014 at 10:31 AM, Lynelle Hamilton <lynelle at lahamilton.com>
wrote:

>  My masonry heater did just fine on this count.
>

Further to Lynelle's point, I did an investigation for CHMC back in 1994 on
air requirments for masonry heaters in airtight houses.
The only technical issue is whether the appliance consumes sufficient air
to depressurize the house enough to cause drafting problems for naturally
vented appliances such as gas water heaters, etc. and thereby cause a
carbon monoxide danger.

Previous CMHC sponsored research had determined a house depressurization
limit (HDL) of -5pa as being acceptable. We measured the actual air
consumption on a number of heaters, and assumed the tightest tested R-2000
house I could find (ELA of 0.02 m2, or 30 sq. in.). Computer modelling
showed a maximum depressurization of -2 pa or well under the limit.
Moreover, when the pressure test is done on a Canadian R-2000 house, you
have to tape up both of the 5" holes from the HRV, because these are
actually leaks in the envelope that are not counted as such. Here is the
study:
http://heatkit.com/html/papers-n/airreq/Cmhc-rep.PDF

On the other hand, if you install an outside combustion air supply on a
stove, and the exterior opening is on the leeward side of the house, a
strong wind can cause the combustion air supply to become a chimney. There
is a famous video of the flames going into the airwash outlet at the top of
a zero clearance fireplace door. In addition, to get clean combustion you
need a hot firebox, and sucking -20F air directly onto the fire is very
counterproductive in this regard.

Norbert
-- 
Norbert Senf
Masonry Stove Builders
25 Brouse Road, RR 5
Shawville Québec J0X 2Y0
819.647.5092
www.heatkit.com
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