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Question about combustion air input on a high efficienct furnace.
wrote:
wrote:
The outside air is "dry" so you'd have to add moisture to get it within
the "comfort zone", which requires additional energy. Using outside air
for combustion reduces or eliminates this energy sink...
Agreed, altho you don't have to add moisture to be in the comfort zone.
You can also raise the air temp slightly. The energy needed to evaporate
water is several times greater than the energy saved with a lower thermostat
setting, unless you live in an extremely airtight house.
Some people would rather not tolerate relative humidity below a certain
level, even if they "feel" warm enough, so "comfort zone" does not
pertain to temperature alone. We agree that constantly replenishing
water in the air generally requires greater energy than the slight
increase in temperature that would make it "feel" just as warm, unless
the humidity lost to air leaving the house can be made small. Sealed
combustion eliminates one of these losses. It is my observation that
sealed combustion can eliminate the need for supplemental
humidification altogether.
It also decreases the potential for air infiltration in certain areas which
would make those areas "feel" cold, inciting the occupants to increase
the thermostat setpoint.
And if exterior walls are warmer, with less inward infiltration, they lose
more heat to the outdoors. And uniform infiltration through wind barriers
could make them act like Scandinavian "breathing walls" with no heat loss
to the outdoors.
That's food for thought, but I remain skeptical that infiltration
induced by non-sealed furnace combustion will significantly decrease
the overall exterior temperature of conventionally built exterior walls
or make them perform like these Scandanavian walls of which you speak.
If infiltration creates cold spots on the interior surface, they'll
draw heat from the room.
It seems to me that even if unidirectional infiltration (i.e. enter
through wall, exit through furnace exhaust stack) were to reduce the
wall exterior surface temperature to outside temp so as to eliminate
heat loss from that surface, it wouldn't eliminate heat loss to the
outdoors altogether. The heat-losing surface has simply relocated to
somewhere within the wall or the living space.
I could see how the R value for a well designed breathing wall would be
unexpectedly high compared to a conventionally framed and fiberglassed
wall, if one's expectations are based on looks alone.
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