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QUESTION:I am replacing a 30 year old furnace and have had some conflicting
recommendations from heating contractors, maybe you guys could help.
House is bi-level, 2000 square feet, brick on block located in Salt Lake
City Utah, good insulation in ceiling, none in walls.
Current setup:
120,000 btu furnace American Standard, 3 ton Whirlpool Power Guard AC
Contractor 1 said a bi-level house should NOT have a 2 stage furnace because
when running in the lower stage all the heat will be forced upstairs.
Recommends a singal stage 100,000 btu, keep existing AC until it breaks.
Contractor 2 recommends 2 stage 100,000 btu, thinks contractor one is wrong
about bi-level house. Also thinks should replace AC. I asked about only
replacing the AC coils, in furnace ducting, and upgrading the compressor
later. He said, "No, you will contaminate the new coils with dirty freon".
He thinks might as well replace AC coils now as will be a major pain,
expense, later.
Contractor 3 recommends 2 stage 100,000 btu. Never heard about contaminating
a new AC coil when paired with an old AC compressor.
So the questions are:
Should a bi-level house have a 2 stage furnace installed?
Can you hurt a new AC coil by running it with an old AC compressor?
ANSWER: While warmer air will rise it still when driven will follow the path of
least resistance. The blower on a higher speed will deliever more air to the
upper floor normally, dependent on duct design. The contamination concern is a good one, the normal compressor failure burns
the windings in the compressor. The resulting contamination will transfer to
your new unit less the amount that can be cleaned with the use of filters.
Also the effiency of newer equipment can be lowered by not useing matched
equipment. Good installation procedure would suggest that the condensor,
line set and coil be matched and replaced at the same time. If he is being honest with you about the contamination issue he likely has
little if any background other than sales. If you aren't ready to replace
the AC keep it as it is there is no reason to replace the coil. If you are
ready to replace you should save money on replaceing both units at the same
time.
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