Ok_Low_1287 t1_j7h32xx wrote on February 6, 2023 at 7:22 PM

Are small mini split type heat pumps really more cost effective given electricity cost vs. other fuel types (oil/propane/gas)??

magellanNH t1_j7h61ni wrote on February 6, 2023 at 7:41 PM

Right now natural gas can be tough to beat with a heat pump, especially when it's really cold out. OTOH, heat pumps are usually cheaper to run than oil or propane, even with today's higher electricity costs.

This website shows how much it costs to heat your house with various fuels given current prices (Look at $/MBTU for comparison)

https://www.energy.nh.gov/energy-information/nh-fuel-prices

The key is to know the heat pump's coefficient of performance (COP) at various temps. COP tells you how much more efficient a heat pump is compared to using a resistive heating element. A heat pump running at a COP of 2.00 costs half as much to run as a heating element. A heat pump running at a COP of 3.0 can heat your house for a third as much as using resistive heat.

Here's a data sheet that shows real numbers for capacity (btus/hr) and for efficiency (COP) for a modern low temperature heat pump at different temperatures (see table on right):https://ashp.neep.org/#!/product/34469/7/25000///0

zeeke42 t1_j7pk7od wrote on February 8, 2023 at 2:33 PM

Heat pumps beat oil pretty well in the shoulder seasons. When it's like 45-50F outside, and they run at low load, they're crazy efficient.

magellanNH t1_j7ppqco wrote on February 8, 2023 at 3:13 PM

Most heat pumps on the market today will beat oil at temps much much lower than 40 degrees. That 40 degree cutover number is from heat pump technology over 5 years old. The industry has really improved low temp efficiency a ton in the last 5 years.

My Bosch unit (installed in 2022) runs with a COP of 2.4 at 5 degrees. With that COP it's still cheaper than oil to run. As temps go above 5 degrees into the 10s and 20s and 30s, it becomes significantly cheaper than oil (as much as 1/2 the cost at higher temps).

Most current Mitsubishi mini-split models, even the non-hyper heat ones, maintain a COP around 2.2 down to 0 degrees or so. At temps above 10-15 F, they're often closer to a 3.0 COP and some make it close to a 4.0 COP in the upper 20s and 30s.

zeeke42 t1_j7pt6ca wrote on February 8, 2023 at 3:36 PM

Yeah, they beat oil at the lower temps, but they absolutely wipe the floor with it at the higher ones. COP at 47F on some of the newer LG systems is pushing 6! It's better at 10-15 than I realized though, thanks!