I have received proposals from two reputable HVAC contractors for ducted systems using our existing air distribution system, one specifying Amana MDASZ60361E and the other Mitsubishi SUZ-KA30NAHZ. The Amana option is a couple thousand dollars less. Does anyone have an opinion about differences in the equipment? I am in Madison, WI, so it is cold, but it is a pretty well insulated, 1923, 1000 SF house and needs about 15,000 BTUH at -7 F. Backup will be electric.

Some more background information. Since electric resistance is the backup (ducted), the contractors are trying to get the heat needed at very low temperatures, which is why the units are large.  Heat load calculation is based on back calculating from the current worst month BTU per HDG natural gas use. It matches the Slant Fin program calculation (that I happened to still have on my computer when I did some radiant heating work in the past) pretty well, about 16k-17k BTUH at -7 F. We are disconnecting the gas, since the connection fee is more than the gas use fee and we have the ability to cover the electric with expanding our photovoltaic system. 

Final bit of backup information. Our PV system is grid connected. We have a pellet stove that can keep the house warm during an extended power outage with backup electricity, so we don’t need the natural gas connection that costs over $250 per year just to be connected. The contractor specifying Amana said the next size down is 24k (SZ60241E) for $800 less installed. That unit is rated for 13k at -10, so we would be switching to electric resistance at a warmer point than that, maybe 0 to – 5 F. But still, maybe it wouldn’t be a large difference over the winter. Just for background information, I’d like to replace our furnace, anyway, since it is a Heil high efficiency unit over 35 years old with no A/C. I work for a solar energy installer, so can expand the PV system pretty inexpensively. The existing furnace is oversized at 45k BTUH and doesn’t modulate at all, but other than a little overshoot when it cycles in the shoulder seasons, it hasn’t been uncomfortable for us. This should be an improvement.