You may have read my other post re oil furnace size, I've been given another option that sounds great but there's more questions. Got a great quote from a contractor, highly recommended, who (at one visit) appears very competent. Did a Manual J calculation and came up with 48.5k heat loss at 70 deg and avg infiltration (1.05 ac/hr), 42.7k with a tight house (.4 ac/hr). I feel the house is somewhere in between.
Also the comp is based on 0 deg that we get only rarely here in RI and we have alternate electric baseboard heating if necessary (though not desirable to use).
So, the issue is two choices: Amana AMV 9045 that goes 44.3k at high fire and 30.8k low, or AMV 9070 that yields 66.9k and 46.4k. We lived with a way oversized two stage gas furnace in a past house, that never ever went to high fire...doesn't make much sense to own high speed when you're never out of low.
On the other hand, the AMV 9045 might never catch up on the worst of days that happen kind of seldom. Am I incorrect in thinking that max efficiency comes from constant high fire at the worst expected conditions? I would imagine most of the time on cold days the furnace would run almost constant in low with occasional high fire...is this good to go?
The real issue is I'd love to have about a 50k furnace but none is being quoted. I have to make the decision here to go with this very efficient gas furnace, or to replace the existing oil with a Thermopride OH6 that provides 60k at low fire.
I really don't want to overfurnace but the spread between the 9045 and the 9070 have me forced to make a tough choice. Suggestions?