Q: The dealer we talked to told us if we go with a vent-free system it is recommended that we leave a window open in the room? Is this true?
A: Your dealer is partially correct. All gas burning appliances (vented
and vent-free) need fresh air for proper combustion. If your house is
of very tight construction, then you will need to provide air into the
room to replace that which is being consumed in the combustion process
(the burning of the gas). Vent-free gas logs and heaters are considered
to be "supplemental" heaters, not your primary source of heat. The
longer the vent-free gas log or heater is operated, the more the need
for fresh air.
On the other side of the issue is to consider whats left over after
the gas is burned. The vent-free standard limits the amount of gas that
can be burned, and Chilbuster burners are very efficient, so the amount
of combustion products is quite low compared to other gas appliances,
but still, there are combustion products (water vapor, Carbon Dioxide
and small amounts of Carbon Monoxide are the largest components). You
can either dilute them or vent them. Fresh air will dilute them, and
cracking your damper will vent-them (but will also send some of the heat
out of the house and up the chimney).
Your nose and eyes can be you guide as to whether you need to open a
window and/or crack the damper. Since vent-free gas logs draw the air
it needs for combustion from the room, any impurities in the air (like
dust, cigarette smoke, pet hair, incense, scented candles, off-gassing
from new carpet, paint or varnish, etc.) will be recycled through the
flame and be sent back into the room as odors, which are most noticeable
in the absence of fresh air. Even without any of these influences,
there is a natural odor of
combustion, to which some people are more sensitive than others. Water
vapor condenses on cold surfaces (like windows and walls) when not
diluted or vented (just like in your bathroom after taking a shower).
In all such cases, "dilution is the solution", and/or slightly opening
the damper to vent the combustion products.
Slightly opening a window may provide enough fresh air. If your
home is very active, with people opening and closing the doors to the
outside often, or if your home is older and drafty, then you may
naturally have enough fresh air input.
In summary, vent-free gas log sets can be a very good source of heat
for a room, but like all heaters, you need fresh air. Slightly opening
a window and/or slightingly opening the damper can be the solution to
the need for fresh air or to reduce any odors from having a tight house
or impurities in the air.