On 9 Mar 2006 07:05:01 -0800, wrote:

dnoyeB wrote:
RayV wrote:
I'm with you the OP said "...the previous owner had disconnected some
ductwork (4") which connected to the cold air return of the
furnace...". That doesn't sound to me like it is being used for
combustion.


Yes and no. I have such a connection in my home. There is a 4" or so
duct that is piped into the return duct. That 4" pipe comes from
outside. So anytime hot air leavs the house through the roof, or the
bathroom fan, or furnace/hot water heater exhause, the cold air sucked
in is through the furnace. (in theory)

Its not directly used for combustion, but its for pressure equalization.
The air used for combustion which is exhausted is replaced by air coming
in from this pipe and into the return.

--

Boy, I'd disconnect that crap real fast. This is an energy disaster.
What makes you think outside air is only coming in to equalize pressure
when air is leaving via say a bathroom fan? In reality, the powrful
furnace blower is gonna draw outside air in all the time. And the
inside air will make it's way out, via things like the bathroom fan,
whether it's turned on or not, or any other ways to exit the house.

A normal house shouldn't need any air specifically brought in from the
outside when the furnace is heating/cooling. Housed get enough from
existing air leaks around doors, windows, opening/closing doors, etc.
If you have a high energy efficiency house that is sealed very tight
and you need more outside air, then an arrangement with a heat
exchanger is used. Anything else is just wasting a lot of energy.
IMO, the arrangement you have is similar to leaving a window partially
open.


You obviously never heard of Sick Building Syndrome! Indoor air is highly
polluted and needs a replenishment of fresh air. In the winter time the
house is usually shut up more than in the summer and contaminants just
build up. This is especially bad if someone has allergies to indoor
contaminants, a growing cause of asthma! Also the air exchanged with
opening a door is contributing unheated air to the house. The outdoor air
supply is being heated before entering the house.

http://www.epa.gov/iaq/pubs/sbs.html