If you are a little handy, IMO there's not much to be gained from an annual inspection, and twice a year is definitely not worth it. Have a working CO detector, regular filter changes, clean the outside coil annually (easy), make sure the condensation drain is working, take a look at the >inside< AC coil every few years and clean >it< if necessary (use the correct cleaner, see the coil manufacturer's recommendation), visually inspect the heat exchanger for cracks.
The one exception IMO would be an oil furnace. They tend to burn dirtier than a gas furnace and the burners sometimes need cleaning/adjusting. Their flue temperatures (esp older, non-condensing models) tend to be higher than the temperatures for gas furnaces, which can lead to accelerated rusting of the flue, etc. The flue should be checked for residue buildup, integrity of connections and of the pipe itself, etc. A once-per-year inspection would seem plenty to me.
Disclaimer: I'm not a certified HVAC tech or even especially knowledgeable on this stuff.
The one exception IMO would be an oil furnace. They tend to burn dirtier than a gas furnace and the burners sometimes need cleaning/adjusting. Their flue temperatures (esp older, non-condensing models) tend to be higher than the temperatures for gas furnaces, which can lead to accelerated rusting of the flue, etc. The flue should be checked for residue buildup, integrity of connections and of the pipe itself, etc. A once-per-year inspection would seem plenty to me.
Disclaimer: I'm not a certified HVAC tech or even especially knowledgeable on this stuff.
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