Subject: Re: Depressurization-induced backdrafting

From: [email-masked] (Simon White)
Date: Sat, 29 Jul 95 18:26:41 GMT

The general approach to the problem in the UK is to avoid the use of
open-flues gas appliances by using appliances of the balanced-flue type.

With regard to extract fans and open-flues appliances the situation is
clearly set out in Approved Document F of the Building Regulations. To
quote from same:

Interaction of mechanical extract ventilation and open-flued combustion
appliances

1.8  Mechanical extract ventilation can cause the spillage of flue gases
>from  open-flued combustion appliances in dwellings whether or not the
fan(s) or extract air terminals and combustion appliances are located in
the same room. Such spillage of flue gases is dangerous and in dwellings
where it is proposed to install open-flued appliances and mechanical
extract ventilation the appliance needs to be able to operate safely
whether or not the fan is running. For example with:

a.  gas appliances, where the appliance and the fan are located in the
kitchen, the maximum extract rate is 20 litres/second. A spillage test
as described in BS 5440: Part 1, Clause 4.3.2.3 should be carried out
whether or not the appliance and the fan are in the same room. Where a
fan causes an appliance in a different room to spill, the extract rate
may be reduced to cure the problem. (Further advice is contained in
BRE Information Paper 21/92.)

-- 
Simon White
[email-masked]

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From: [email-masked] (Allenbau)
Date: 29 Jul 1995 19:51:35 -0400

To be fair, I'll say that I've seen vented combustion appliances backdraft
in homes, so I know that backdrafting exists.  I view backdrafting as a
health hazard because of the potential for exposure of occupants to carbon
monoxide and other pollutants.  I'm unsure whether existing codes are
adequate -- they just might not be adequately enforced.  Homeowners are
also resonsible to some degree --furnaces must be tuned periodically so
they burn clean and efficiently.

Oh joy - another researcher studying the obvious -> another silly assed
law -> another agency to "help" us.

Mike Allenbaugh

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From: [email-masked] (Mike Ivanovich)
Date: Mon, 31 Jul 1995 08:55:50 -0700

In article <[email-masked]>, [email-masked] (Allenbau)

> law -> another agency to "help" us.

Mike A. -- from your posts to other messages on this board, I would have
expected something more from you than a flame if you were going to respond
at all.  I gather from your posts that you have experience and a firm
grasp of reality that could help check pie-in-the-sky solutions.  I'm
disappointed that you so casually dismissed my inquiry.

I think its obvious that backdrafting exists and that it's a health hazard. 
But there are many who contend that backdrafting is a needle in a haystack
-- and that air coming down the chimney is diluted with outside air to the
extent that it is not a health hazard, or if high levels of CO are found,
the chance for exposure that induces health effects is so miniscule, that
it hardly merits any attention at all.

In other words, researchers have to be prepared to present a case with
much more in hand than a statement as to what they think is obvious.

And so I'm inquiring you -- and others that read this board -- to offer
both sides of the issue.  I've seen and heard backdrafting/CO argued
between researchers and industry representatives, but not among the people
who install systems or among those that respond to occupant complaints of
CO.

What's obvious to you, Mike?   Like you, I think that the U.S. has
probably 2 billion laws we could do without -- that "law is suffocating
America" (from the very persuasive book, Death of Common Sense).  So,
then,apart from laws, how are problems, like backdrafting eventually
resolved?  Getting to solutions of that nature requires digging --
thinking -- communicating.  Communicating -- like asking those out in the
field what they are experiencing -- asking them if they have ideas for
solutions, etc.  This newsserver could be a great forum for batting around
good ideas and experiences.

I hope to hear from you again.

Mike I.

-- 
_________________________________________________
Mike Ivanovich, Senior Research Scientist, PNL 
Opinions expressed are my own, but you're welcome to them.
email:  [email-masked]
phone:  (509) 375-4584        fax:  (509) 375-3641

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From: [email-masked] (paul milligan)
Date: 1 Aug 1995 01:31:31 GMT

In article <[email-masked]>,
   [email-masked] (Mike Ivanovich) wrote:

~~>I think its obvious that backdrafting exists and that it's a health hazard. 
~~>But there are many who contend that backdrafting is a needle in a haystack

	I've never heard this statement before, and I'm amazed that anyone
would present it.  The point is not the OA coming down the flue ( which you
would breath outside anyway ), it's the combustion gases introduced into
the living space, and the roll-out fire hazard.

	Roll-out can EASILY light a building and kill people.  Especially
considering how many idiots who pretend to be service techs run around
bypassing safeties.  This is not a 'needle', unless maybe the one you sit on,
which suddenly takes on a greater signifigance in your life than the one
you missed.  :~(

~~>-- and that air coming down the chimney is diluted with outside air to the
~~>extent that it is not a health hazard, or if high levels of CO are found,
~~>the chance for exposure that induces health effects is so miniscule, that
~~>it hardly merits any attention at all.

	Crap and more crap.  Are there actually people who say this and
mean it ?  Tell it to the two people who died from back-drafted CO
in Raleigh, NC, a few years ago.  Tell it to the many others who died.

	Mike I., can you tell us where you hear people saying this ?
Are they industry people ?  In what forums can they propound this deadly
nonsense ?

Paul

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From: [email-masked] (JaredM)
Date: 1 Aug 1995 21:59:34 -0400

In article <[email-masked]>, [email-masked] (David A.
Jump) writes:

>Is it true that an induced-draft furnace (maybe we need a glossary of
terms!)
>draws inlet air for combustion from the space surrounding it? 

Most, if not all 80% furnaces are induced draft (there are a few
exceptions) and use the space surronding them for combustion air.  This is
the reason for the ventilation requirements that are clearly spelled out
in the paperwork for every furance sold today. Sadly, these ventilation
requirements are rarely enforced, at least in my area.  When I say
ventilation here I am talking about ventilation for combustion and not
fresh air for the occupants.  Most 90% furnaces have the ability to be
sealed combustion, meaning that air for supporting combustion is brought
directly to the combustion chamber.  Some 90% furnaces are able to use the
air in the utility room, however unwise that may seem.

>I'm not exactly sure what a draft prover is.  Does it provide OA directly
to
>the furnace, effectively separating the combustion air from the house?

The draft prover in this case is a micro switch connected to a diaghram
that senses a slight negative and/or positive pressure created by the
draft inducer fan.  The ignition sequence is started after this sensor
makes a circuit proving that the fan is on and creating a draft.  These
switches fail with some regularity.  Because there are a number of brands
and models of furnaces that the typical residential service tech
encounters, it would be next to impossible to stock every one on a truck. 
Hence the temptation, as Paul mentioned, to jump the switch creating a
potentially dangerous situation.  The same applies to roll out switches
and spill switches. 

 I find that in many case these switches are simply doing their job due to
a weak or marginal draft.  Of course they are immediately blamed because
they are the obvious problem, not the true underlying one.  For example, I
remember last winter having a furnace that occasionally went out on the
draft prover, it would relight, run for a number of minutes and then fail
again.  Another company blamed the draft prover, it was replaced and the
problem remained.  I found a mouse and two birds in the flue pipe between
the furnace and chimney.  I also remember that customer complaining about
our service bill, we were a bit higher than the other firm.  Some people
can't see the trees through the woods.

---

From: [email-masked] (Allenbau)
Date: 31 Jul 1995 21:46:44 -0400

OK - you're right - I came on pretty strong. We do see a lot of buildings
that are running at negative pressure (residences included because of
exhaust fans, vent fans, range hoods, etc.).

Seems that negative pressure is usually considered when a building is
erected but future modifications often fail to take into account any
changes in the static pressure that may result. I think the solutions are
usually obvious (hence my remark) but obviously some of us are not doing
the obvious.

I have become an advocate of induced draft for any unit that burns fuel
inside the structure because they work in spite of most building problems.
I doubt that you have seen a backdraft in a system where an exhaust fan
and a draft prover were used. The new higher efficiency furnaces take this
into account and solve the problem for that one unit even if not for the
entire building.

A commercial building using economizers is a moving target because of the
varying use of outside air. Most economisers only change the amount of
outside air entering the building - some of the better engineers and
contractors on this forum probably adjust exhaust air to closely match
intake air but it is not real common. It is very hard to sell.

I installed several good size units and a bunch of smaller ones in a
hospital where the pressures must be closely monitored and controlled in
order to exhaust air that may be carrying undesired microorganisms. I
thought it was interesting that we had to install additional separate
venting for rooms designated for patients with airborne contagious
diseases when it was already the rule for the entire hospital.

This was my complaint about extra law - we took rooms that met the code in
every way except for the fact that they were designed correctly in the
first place. The law does not allow for that. We had to install additional
venting because we were required to have the hardware attached to the
room. In our case we didn't even have to turn the new equipment on in
order to comply with the law but we did have to install it and verify IN
WRITING - DAILY that EACH affected room was venting properly.

My experience has been that static pressure sensors are not very linear or
reliable so it takes a lot of care to keep a large building balanced out.
With the advent of tighter residential construction I think it would be
nice to have an "off the shelf" item to test for  pressure inside and
outside the house.

Finally - In a large building you may have doors blowing open or doors
that are hard to open or even people with unexplained allergies but the
three families who died in this county last year died at home breathing
fumes from their own furnaces.

Hopefully, your solution will be elegant (simple) and usable in residences
where people die as well as in larger buildings where we may be
inconvenienced or even become ill.

Please forgive me for the flame - I went off 7/16 cocked.

Mike Allenbaugh

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From: [email-masked] (Ken Irving)
Date: Tue, 01 Aug 1995 21:49:28 GMT

In article <[email-masked]>, [email-masked] says...

snip

>intake air but it is not real common. It is very hard to sell.

IMO the idea of "statically" linking exhaust to intake air (e.g., via damper control signals) is 
not sound.  There are so many variables involved, with damper linkages, etc. - rather, the 
answer is *active* static pressure control.

snip
>nice to have an "off the shelf" item to test for  pressure inside and

IMO modern static pressure transducers *are* reliable and very usable, and a key part of any 
static pressure solution.  Linearity should not be an issue; if the device is reasonably 
accurate at the desired control point, then it can be used for control.

>fumes from their own furnaces.

I'd say *none* of these situations are acceptable.

>inconvenienced or even become ill.

Yes, indeed.  My experience is with non-residential work, but with the progressing technologies 
higher levels of control *ought* to become more accessible at lower cost.

A related topic to this is the current emphasis on residential ventilation systems, sometimes 
with heat recovery.  These systems *could* easily be adapted to active pressure control in 
residences.

Ken Irving

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From: [email-masked] (David A. Jump)
Date: 1 Aug 1995 23:59:37 GMT

In article <[email-masked]>, [email-masked] (Allenbau) writes:
|> 
|> I have become an advocate of induced draft for any unit that burns fuel
|> inside the structure because they work in spite of most building problems.
|> I doubt that you have seen a backdraft in a system where an exhaust fan
|> and a draft prover were used. The new higher efficiency furnaces take this
|> into account and solve the problem for that one unit even if not for the
|> entire building.
|> 

Very true, however the difference in cost between the new > 90% AFUE furnaces
and the ~ 80% furnaces can be as high as $500.  I don't think you'll start
seeing these models in new tract construction unless the cost comes down a
bit.  For those who are aware of these IAQ issues, or are concerned about
energy efficiency, the cost may be worth it to them.  My experience is in
California, where the housing market is not primarily driven by energy efficiency
or IAQ considerations.  Maybe someone else can tell us whats going on in
colder climates.

Recently I was searching for an inexpensive commercially available 
directly-vented furnace, i.e. one with ducted inlet and outlet combustion air,
which would forever (pending proper operation) separate house air from the 
combustion.  Some here may recall my queries on alt.hvac, before the creation 
of this group (and once again, thanks to all who provided me with some valuable 
information). From this correspondence, and from talking with a few manufacturers,
I've found out that inexpensive residential directly-vented AFUE furnaces aren't 
available.

Is it true that an induced-draft furnace (maybe we need a glossary of terms!)
draws inlet air for combustion from the space surrounding it?  If so, then there
is always the potential for backdrafting.  I'm talking about worst case scenarios,
where perhaps all of the exhaust fans in a tightly sealed house are on.  Some of
the newer exhaust fans are strong, moving up to 50 cfm or more.  With a few of 
these in a house the potential for problems is there.

I'm not exactly sure what a draft prover is.  Does it provide OA directly to
the furnace, effectively separating the combustion air from the house?

my 2 cents,
David

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From: [email-masked] (Allenbau)
Date: 1 Aug 1995 21:09:31 -0400

>I've found out that inexpensive residential directly-vented AFUE furnaces

We've had great success in Iowa with the following:
1 - build a small room around the furnace
2 - Run insulated duct from the outside to bring combustion air to the
furnace
3 - drop the air into the furnace room  several feet from the furnace so
the cold air won't crack the heat exchanger.
Doesn't solve every problem in the world but customers like it and report
more comfortable and cheaper heating (no one has ever quantified either
term). Furnace does not draw a vacuum on the house.

> the furnace, effectively separating the combustion air from the house?

Draft prover is a device in the exhaust flue that senses direction of air
in the flue - if there is not adequate air flow FROM the combustion area
TO the outside then the gas valve will not come on.