We have a 2 family home with 2 separate forced hot air heating systems. Recently the main unit died so we figured we'd replace both units. We never heard the old ones heating the home and we were always plenty warm. The new ones cycle on and off every 3 minutes or so. They're noisy and don't warm up the house the way the old units did. They come on with a bang and shut down with a bang. My husband said they both sound like a commercial blast furnace coming on, and our units are in the basement so we shouldn't hear anything.

. It's loud. In the apartment the air coming from the heating vent is sometimes cool and not hot. The main apartment unit cycles on and off too and it sounds like an airplane motor revving down when it's ready to shut off. I have the installer coming back AGAIN tomorrow. The first time he came he lowered the air flow but it didnt help, the second time he came he told us to change our air filters that were only 2 mos old which we did, and it didn't do anything to help. Can someone give me any insight into what they think is going on with these units please?

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    What type of system - natural gas? heat pump? Make/model #? What size (kW or BTU or ??) What city or area are you in (to get an idea of climate)? Approximately how many square feet heated by each unit? Feb 11, 2022 at 4:13
  • It should be a separate question, but what kind of air filters? Many are designed to be replaced monthly, so replacing it after 2 months might be too late, not too early.
    – FreeMan
    Feb 11, 2022 at 13:00
  • natural gas. The model is the RunTru by Trane and it's the same BTU's as our old ones. The filter calls for a 'high velocity filter' but nobody seems to know what that is. Recommended filter size is 24x24x1 for return filter but we only have a 14 x 18 inch opening in the unit for the filter. The return is only open on one side.
    – RonG
    Feb 12, 2022 at 17:13

2 Answers 2


The banging noise could be from the new sheet metal plenum box that the installer put between the new furnace and the old ductwork. Also, the old ducts could have added stress from the new plenum. Stand nearby to listen for the bang. Be sure there is a flexible collar between the old and the new sheet metal.

Thermostats have an anticipator setting that must match the furnace. It could be adjustable for type of furnace or for length of delay. The motor noise and rumble could be reduced by installing some rigid fiberglas duct liner in the plenum area. It is a sound dampener that goes inside the plenum area.


Did your installer do a proper professional assessment of the heating needs of your systems and size them appropriately? (I think this is what they call, in the industry, and Manual-J calculation). This takes into account the region, windows, insulation, conditioned size, and probably other factors that impact the amount of heating or cooling needed).

What are the BTU ratings of these new units compared to your old ones? Were perhaps your old systems higher-end with variable speed fans, which tend to be quieter than the one-speed ones that are less expensive?

It's possible they installed much larger units (BTU-wise) than what you had before, and these new ones are way too big for your space, and so they're short cycling. Ideally heating systems (and cooling) should be sized so that at their maximum expected need they're running close to 100% of the time. If your furnace is oversized, you'll get short cycling in the winter, and if your A/C is oversized, you'll get a cool, but humid interior in the summer since it won't have time to pull out a lot of humidity before you get to the temperature set point.

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