Mitsubishi system.

[MGWillia]

Originally Posted by DRH

Frank - We had two Mitsubishi Mini-Split units installed in 2013. In cold weather when the units are in heat mode, the fins on the outside unit (compressor) can accumulate frost due to the extremely low temperature of the coolant running through them.

However, the units are programmed to sense this frost buildup on the compressor fins and to automatically go into a "defrost" mode that melts the accumulated frost.

During the defrost mode, the outside unit runs but the fan in the inside unit does not run. The system circulates the coolant, extracting some heat from the air in the house and using it to defrost the fins on the outside unit. (The fan on the inside unit does not run during the defrost mode so as not to blow cool/cold air into the house.)

On our two systems, we can tell when they are temporarily running in defrost mode as we can hear a "gurgling" sound coming from the inside units. The defrost mode only lasts for a minute or so, after which the system reverts back to the normal heat mode. On very cold days the units can go into temporary defrost mode a number of times during the day.

If this is not the way your system is operating, then a call to HEP is in order, if you have not already done so.

Please let us know how you make out.

Hi Frank. If I may ask, how big a space are you heating/cooling with two units? Do you feel they are cost effective to run? Are you running another system too? And if you don't mind saying, about what did a two unit system cost you? (Yeah, you get the big list of questions as you give the most indepth answers )

[DRH]

Originally Posted by MGWillia

Hi Frank. If I may ask, how big a space are you heating/cooling with two units? Do you feel they are cost effective to run? Are you running another system too? And if you don't mind saying, about what did a two unit system cost you? (Yeah, you get the big list of questions as you give the most indepth answers )

I think you may have intended to address your questions to me, so I'll provide some info.

We have one 18K and one 12K mini-split units. both of which were installed in August of 2013. The 18K unit heats/cools about 1,600 sq. ft. (first floor) and the 12K unit heats/cools about 900 sq. ft. (second floor). We also heat with a wood-burning fireplace insert and and an oil-fired hot water heating system.

The heat pumps supply about 90% of our heat on the second floor and probably about 70% of our heat on the first floor. A bathroom on the second floor is on its own oil system heating zone, and the oil system supplements the first floor heat pump in three relatively small rooms that are off a hallway on their own zone. Those are the only rooms that still utilize oil heat.

During the heating season we run the wood stove/insert on the first floor most days when the outside temperature is 35 degs or below, especially if it's windy, and every evening. We typically burn about two cords of firewood each winter.

Looking over our New Hampshire Electric Coop (NHEC) electrical bills for the 2012/2013 and 2013/2014 heating seasons, I estimate that the winter heat pump operation increased our overall electricity expense by about $600 during the 2013/2014 heating season. (Our useage of the wood-burning fireplace insert was approximately the same during both heating seasons.)

Offsetting the increased electricity cost was a significant savings on heating oil. I estimate that we burned approximately 750 fewer gallons of heating oil during the 2013/2014 heating season than we did during the 2012/2013 heating season. Based on today's going price of about $3.00 per gallon for home heating oil, that equates to a savings of $2,250 due to the use of the heat pumps in the 2013/2014 heating season.

Therefore, the effect of the heat pump installation in August of 2013 was a net cost savings of about $1,650 to heat our home during the 2013/2014 heating season compared to the previous year.

The total cost for the installation of the two Mitsubishi Mini-Split units in 2013 was $7,500. However, NHEC provided an $1,800 incentive rebate check, and the IRS allowed a $300 energy credit on our 2013 Federal tax return. These two credits reduced the net cost of the heat pump installation to $5,400.

So, it appears that the heat pump installation at our house will likely pay for itself in 3.3 years. The Mitsubishi units come with a 7-year manufacturer warranty.