Dec 8/08

Hi Bruce:

An interesting post today on John Gulland's woodheat list on Yahoo. It pretty much sums up why there is
confusion on the subject of outside air. I'm in agreement with John's assessment.



--- In, "John Gulland" <john@...> wrote:

Hi Stewart,
You are in an awkward position there. As I understand the
situation in Quebec, the national building code is used in
the large cities but the small municipalities have not
adopted a building code. I could be wrong about that,

No, I haven't seen anything new on the subject of outdoor
combustion air for a few years. The last work I did on the
subject was in 2003 as part of a delegation made up of a guy
from the National Research Council (building code) and a guy
from Canada Mortgage and Housing which attended committee
meetings of the oil and gas heating appliance standards
committees to try to convince them to give up on their
requirements for outdoor air (which are based on wishful
thinking, not science) and harmonize with the wood heating
appliance installation code which does not require outdoor
air, but says if there is a problem, you have to deal with
the pressure in the house. But the oil and gas heating
industries are in denial and haven't done anything to my

The national building code and the ventilation code are
vague and quite confusing on the subject and I think still
offers outdoor combustion air as an option. One of the
problems is that all factory-built fireplace manufacturers
dutifully include instructions and fittings for outdoor air
supplies for their products. They have no choice: if they
didn't, they wouldn't have access to a lot of markets in
North America. Note that factory-built fireplace instruction
manuals are what all installation codes rely on for the
authoritative rules for specific fireplaces.

The housing industry is resolutely in the mandatory outdoor
combustion air camp. It makes sense for them because it is a
relatively cheap fix, and whether or not it works, it does
obsolve them of any further responsibility.

To my knowledge, there has never been a scientific study
demonstrating that outdoor air supplies, whether indirect to
the room or direct to the combustion chamber, can reliably
prevent smoke spillage or backdrafting. There are a few
studies showing that they don't do much of anything positive
and can cause problems. By applying fairly straightforward
aerodynamic theory, this result is easily predictable. See:

You may be forced to install outdoor air (that is, put a
hole in your house) to satisfy everyone involved. If it
causes you problems later (and it might), you can plug it

I guess you could say my years of effort to convince people
that basing installation rules on science rather than
opinion is the way to go qualifies me as passionate on the
subject. But I reject the idea that this is a case of my
opinion against other peoples'. I am still waiting for
someone to fund a study showing the effectiveness of outdoor
air supplies.

It should be said that despite all of my efforts (and other
peoples') since the early 1990s in articles, discussion
papers, countless presentations to industry groups and
training sessions, I have been spectacularly unsuccessful in
convincing most of the people and agencies involved to
revise their approach to outdoor air. The science-based
housing agencies in Canada have spearheaded some changes,
but almost nothing has changed in the US.

I have now moved on and spend almost no time on the subject.

> -----Original Message-----
> From:
> []On
> Behalf Of stewabbey
> Sent: December 9, 2008 8:41 PM
> To:
> Subject: [woodheat] Outdoor combustion air
I am about to install a Valcourt FP 8 EPA certified fireplace in a
fairly tight new house. I have read "The Outdoor Air Myth Exposed" at I agree and respect the article but my builder and even
my HRV guy are trying to convince me otherwise. They are saying it is
a Canadian code. I'm in Quebec, I believe outdoor combustion air is
code in Ontario but I didn't think it was so in Quebec. I Have no
inspections where I am building so it would only be for insurance
reasons and to satisfy my builder. John, is it code in Quebec? Have
the codes for outdoor combustion air been taken away in very many
places yet? Can you give me anything new to show them since the
outdoor air myth was written? I know you are very passionate on this
subject. Has anyone else ever experience the need for outdoor air or
vise verse?

> ------------------------------------

--- End forwarded message ---

On Wed Dec 10, the following exchange followed on the Woodheat list at Yahoo:

RE: [woodheat] Re: Outdoor combustion air on mid efficiency central furnace(oil, ng, propane).

Sam wrote:
> If it is
> a sealed combustion
> chamber, then you need the air supply. You would
> not be able to
> tell if there was backflow until the police are
> there with the meat
> wagon.

(John Gulland replies) :
Sam, I usually think your posts are thoughtful and based on
something factual. Not this time. The above statement is
based on nothing but a religious kind of faith in a hole in
a wall. Worse, it employs exactly the same fear tactics that
have been hurled at me over the years by people who refuse
to cite any data to support their belief in the magic of a
hole in a wall. As I have said over and over to those who
make such wild claims with absolute certainty: show me the
test results.

A quick story.

I was called two years ago by a local oil heating contractor
to help diagnose a persistent spillage problem with an oil
furnace and water heater. They were in a nice, fairly new
house owned by a nice retired couple who had experienced
such severe backdrafting of the oil appliances that it was
once brought to their attention when he noticed that his
wife had black soot marks on her upper lip from breathing
sooty air.

The oil furnace and water heater were installed exactly
perfectly -- and I mean text book, right down to the
provision of two (2!!) 5" outdoor air supply ducts with
loops at their base. I set up my manometer and then started
turning on exhaust devices: the oil furnace and water
heater, an HRV, two bathroom fans and a kitchen range hood.
For an overview of the procedure I used, see:

As we stood in the kitchen reading the 15 pascal
depressurization (very high) that was mostly caused by the
range hood, a smoke detector in the basement family room
went off and we scampered downstairs to investigate, only to
find the basement filled with acrid black smoke. Because of
the severe depressurization of the house, there was somewhat
more air flowing through the outdoor air ducts than there
had been before the test started, but it was not even close
to enough to compensate for the exhaust flows. This result
could have been predicted easily by using a simple equasion.

The homeowners and heating contractor were slackjawed,
gobsmacked, as they say. Once we cleared the smoke, I took
them back upstairs to the kitchen and showed how, if the
range hood was never turned up past 1/3rd speed on its
control, the house pressure would remain within the allowed
limits for oil burners. Alternatively, if something burned
on the stove or something cooking needed maximum speed, the
window right next to the stove could be slid open about 3"
to neutralize the pressure enough to be safe.

The point of the story is that all the air supplies provided
was a false sense of security, but nothing to prevent a
hazardous situation. The installation codes that require
these 'combustion' air supplies and nothing else are
dangerous, and those who maintain them despite knowing that
they don't work are irresponsible. But, hey, they are cheap
and that is what's important, right?


Norbert Senf---------- mheat(at)
Masonry Stove Builders  
25 Brouse Rd.
RR 5, Shawville-------          
Québec J0X 2Y0-------- fax:-----819.647.6082
---------------------- voice:---819.647.5092