On 2005-11-11, wrote:

Wayne Whitney wrote:

Perhaps using colder combustion air results in colder flue gasses?

Which leads to cooler air from the register.

That may be, but doesn't lowering the temperature of the flue gasses
increases the fraction of water vapor in the flue gasses which
condense, improving the efficiency? It's not clear to me which effect
would be greater.

Cheers, Wayne