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Considering new 'hyper heat' Mitsubishi mini-split for Boston addition - advice?

Considering new 'hyper heat' Mitsubishi mini-split for Boston addition - advice?

Old 08-29-18, 07:42 AM
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Considering new 'hyper heat' Mitsubishi mini-split for Boston addition - advice?

I'm adding on to my house. Basically, I'm increasing the square footage about 50% and adding two rooms (one on top of the other).

We had a plumber come out yesterday to plan/quote adding radiators to my existing system. We have a natural gas burner (about 5 years old) and a steam radiator system.

He recommended we go with a Mitsubishi hyper heat mini-split system instead. The reasons were:
1) Provides a/c in addition to heat
2) More convenient than trying to run new pipes/place radiators in new room
3) Won't disrupt the current system, which is perfectly balanced and works well

Now my obvious concern is that heat pumps are traditionally not efficient at very cold temperatures. I had one when I lived in Virginia (many years ago) and it required an electric coil backup in the air handler to keep up when the air was below freezing. The outside unit froze up a lot as well, and would require a defrost period.

The plumber told me the new "hyper heat" systems are rated down to -13F and that the ambient heat from the adjacent rooms would mean we'd be very comfortable.

Has anyone had experience with one of these systems in Boston winters? I don't believe I've ever seen the thermometer hit -10F or below, but I don't want to be cold in the winter time. We usually keep our house at around 68F in the winter
Old 08-29-18, 09:31 PM
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I'm not familiar with the "hyper heat" systems. Mostly a lot of service techs here..... myself included.
Heatpumps have gotten much better and are able to extract more heat from colder ambient temps.

I'm somewhat biased as we have great natural gas prices and what I'd consider higher than average electric rates. Therefore I tend to lean towards fossil fuel heating. If you were trying to heat the entire house with a heatpump..... I'd be a little leery but you basically need it for supplemental upper floor heating as a lot of heat will rise from the lower levels.
Old 08-30-18, 10:54 AM
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I live near Boston and installed two Mitsubishi "Mr. Slim" mini-splits several years ago to replace window/wall AC units in a family room and in a master bedroom suite (converted attic). The mini-splits are heat pump units designed to provide heat down to -13 degree outside temp. Although I was not familiar with the terminology, the specs say that the units use Hyper-heating inverter technology to drive the compressors.

In both cases these are not the primary heating units. I have used the mini-split to heat the family room sometimes in the evening when the main house zone is set back. The outside temperatures were in the 10 degree range and the unit had no problem providing lots of heat.

The master bedroom suite is a separate zone on my hot water heating system and I have used the mini-split to heat the area also when outside temperatures were in the 10 degree range. The area was set back to 55 degrees while I was away for several days. When I returned I used the mini-split to raise the temperature quickly (about 20 minutes) while the house system was coming back to normal (about 2 hours to get from 55 to 68).

In my case the heating is supplemental and optional so the cost difference between natural gas heating and electric is not a critical factor. If you do a heat loss calculation for your addition, you can determine the approximate difference in energy cost.

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