I live in Virginia in a house built in 2002. I have a 6" pipe that
runs from the outside to my cold air return. I have a propane
furnace, but it is not the high efficiency kind that require a
separate line into it for combustion.. I can kind of see a reason to
have this in the winter time, but in the summer is it really
necessary? Also, my 6" pipe is located about 2 feet from my outside
AC unit. When I was having my routine maintenance done, the AC guy
commented on the horrible location saying it would be pulling in even
hotter air with that location. I would love to seal it up during
the AC season, if possible.
Speaking of return, how do they check to see if the return ducts are
pulling air adequately? I know nothing about HVAC systems, but it
seems to me the last intake location in my house is not doing much.
What did your service guy say? The service guy said that was a crazy
location to have an air intake pipe.
My reason for having it in the winter? Here is my uneducated guess:
In a newer house, it is going to be (hopefully) sealed pretty well.
With the furnace using combustion, it seems plausible that grabbing
air from the outside would help supply any extra air for that and
would stop any drafting around the house.
Respectfully disagree, and venture that almost certainly would be against
See.....what if he gets run over by a garbage truck during the summer ?
Suggest a motorized 120vac self opening damper with 24vac relay coil
between W and C--source line voltage so as to always close the damper unless
W is energised
If you want to get real fancy then additionally install a timer....
Also it is there for ANY exhaust needing air intake. For example...bathroom
exhaust fans, microwave exhaust fan, clothes dryer (either gas or electric)
...anything in the tightly sealed, newly constructed house that needs air
make up to work.
On Jun 28, 11:20 am, email@example.com wrote:
Well, from my experience in a humid climate, if you could put a damper
in that intake, it could help lower the humidity in your home.
For it to work, you are going to have to have the furnace fan in the
"Auto Mode" so that it just runs when the compressor runs.
What will happen is that whenever the AC runs, some fresh air will get
drawn in directly to the AC system. The heat and humidity of this air
goes right to your cooling coil, and you end up pressurizing your home
with dry air. Dry air will try to leave your house rather than warm
humid air infiltrate into your house.
You would adjust the damper and open it up enough so that when the AC
was running, you could just notice cool air leaving from a door that
was cracked open.
If your house leaks like swiss cheese it will not work, but if it is
reasonably tight it could work great.
You cannot run your fan all the time, otherwise you will be pumping
humidity into your house when the compressor is off.
IMC requires combustion air for commercial systems.
Some residential codes may require it as well.
I use them everywhere, unless an ERV/HRV is installed.
Here in MN. I've seen lots of them drop down the wall into a 5 Gal. bucket
or looped back up to act as a P-trap & stop cold winter air from flooding
in. Direct into the return works as well, but if it faces north or west,
runs the risk of winter winds blowing into the return, etc...
Dampering is a possibility, but a gas dryer, stove, or water heater will
need the combustion air year round.
If all of the units are on full fire, the fart fans & kitchen hood are
running, you can backflow the flue gasses & make the whole family sick...
We had a case here last fall of a home owner that installed his own boiler,
bought direct from local wholesaler.
Cops pulled him over thinking he was drunk, took him in for tests & released
He went back home & woke up sick with a family member dead of CO...
Sparky needs a license to wire a panel, but gas lines are anybody's
Make Up Air
Three related but separate issues. Should not rely on one system to do
more than one of those tasks. In some places a fresh air duct to the
return would not be deemed as providing combustion air.
Make-up air is usually required to be induced in to the space via blower.
Combustion should be ducted, & ventilation air is commonly allowed via
infiltration, residentially speaking,
unless there's an inordinate amount of exhaust, in which case MUA is
Take a look at the MN pressurization schedule for all three.
Unfortunately not all officials require them for permitting, & fewer still
know exactly what they're for.
I've seen the shortcuts used, best definite as "liars figure & figures lie"
They end up in the file & act as a CYA for the permitters if something ever
That said, I will again say I wouldn't block it off if gas appliances of any
type are in use...
Especially conventional B-vent natural drafters that could easily backflow
if a dryer or a couple bath fans are in operation...
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