My point was if the furnace is even 50% oversized there would never be enough heat loss for 2nd stage to kick in. The only thing 2nd stage would be used for is faster recovery from setback. Most furnaces are in fact at LEAST 50% oversized. I have a 44k (40k output) furnace (as yous stated, smallest you can buy) that replaced my 88k 80%. Even the 44k is too big, what were they thinking when they originally installed the 88k?
Calculating load based on cycle times on the coldest winter night is great if you live in the house. When you downsize cycle losses decrease, you could actually go a bit smaller than the cycle test indicates. I personally have yet to see a furnace that wasn't at least 50% oversized, much less undersized...
|