DIYbanter - View Single Post - Question about combustion air input on a high efficienct furnace.

wrote:
wrote:

Sealed combustion eliminates one of these losses. It is my observation that
sealed combustion can eliminate the need for supplemental
humidification altogether.

That seems unlikely to me, in a typical US house with 0.7 ACH. Then again,
is there any such need?

My criteria are that if the house holds 45% RH, there is no such need.
It is possible that the houses in question were atypical, but the
sealed combustion was instrumental in this.

A hypothesis that may interest you: the effect of a very large "stack
effect" air loss through the old furnace flue, now eliminated. For
example the flue was 8"x8" tile liner within a masonry chimney. Has
since been lined with a 4" stainless steel "snorkel" for the water
heater, sealed top and bottom (except of course where the 4" tube
passes through) to minimise air movement. This is a very large
reduction in effective thermal mass. I guesstimate that the water
heater flue cools within minutes of burner shutdown and stops drawing,
as compared to the case when the furnace operation kept the tile and
masonry warm enough on average to draw constantly through the generous
passageway.