Quote:
Originally Posted by bigdog
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Current furnace is a Trane X90 is only 17 yrs old, BTU output 60,000.
This is way under-powered for the size home I have (two stories-2800SF)
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That 60K BTU furnace could indeed be badly underpowered, if for example the home is poorly insulated and leaks cold air terribly. But if the home isn't all that old and built to code, 60K BTU could be grossly oversized. For example, my house has about 4,000 sqft of conditioned space over two levels but is kept quite comfortable when it's below zero outside by a two-ton heat pump in just first stage, putting out about 19K BTU/hr. But this is for a superinsulated class house, which your house unlikely is.
The failure of your current system to hold setpoint could be due to just erratic operation of a failing system rather than capacity. The correct furnace size should be determined from a properly done Manual J or other appropriate calculation for the specific house. Don't pick a contractor who isn't willing (or doesn't know how) to do the necessary calculations.
One reasonable way of calculating corrrect unit size is from fuel usage over a suitable period of time. Here is a good article on doing this:
https://www.greenbuildingadvisor.com...nace-or-boiler