Heat Pump Unit
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I have a heat pump but for the most part do not touch for a couple reasons. (1) The system uses the highest amount of amps of anything in our household, those it could be deadly if you forget to first turn the power off. (2) The freon like substance that it uses is hazardous to handle, the tubes are pressurized, and you need a license to even handle it and (3) To service it would require specialize skills and literature that I do not process. Instead, I pay a company to look at every year or two.
In fact, the heat pump is probably the only part of my household that I don't mess with. I have been thinking about this for a while, and if you want to be more mustachian, the best route is probably to leave the heat pump alone and install a secondary, simpler, and easier to understand heating system such as wood stove. With these, you can service it yourself, it is simple to understand, and cheaper to operate assuming you can find a free supply of fuel. In the worst cold winters, use the wood stove instead of the heat pump to heat your house.
Filters
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In regards to filters, I use the cheap fiberglass MERV 4 disposable filters. Like you said, I also did research and the higher rated MERV filters, i.e the permanent ones, actually block too much air from getting to the unit and result in higher electricity costs and lose of efficiency. These fancy filters claim to last "up to 3 months" but in practically, in my house they last only 1 month. The higher MERV filters also claim to purify the air, however, these filters and the heat pump were never design to purify air in the house. If you want purified air buy a portable air purifier for the room you spend the most time in. Thus, I found it better to use the MERV 4 disposable filters to maximize air flow to the heat pump while still filtering enough for the heat pump to function.
One thing I do that I am not sure if it is 100% ok or legit, is that I will actually take a high powered vacuum cleaner hose over my cheap MERV fiberglass filter that is dirty to clean it. Even though this is probably not recommend by the manufacturer, it works surprising well on the low MERV filters and they look pretty clean afterward. Usually, I will do this once a month to the filter when the heat pump is in use. After each vacuuming I will mark a star on it. After 5 cleanings or stars on it, I will dispose of it. Lowes and many of the hardware stores stopped selling the fiberglass MERV 4 filters so that customers would be steered to buy the ultra expensive fancy pants ones that cost $15 a piece. However, you can buy a large box of the cheap fiberglass MERV 4 filters from amazon, and it is a great deal.