Heating systems for new home

[WinnisquamZ]

Curious if anyone will be operating their mini spilts for heating this weekend. If so, please let us know how they perform in this weather


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[Slickcraft]

Our hyper heat units 100% crossover efficiency is at about 0 deg F and they are good for operation down to minus 13 deg and 85% efficiency. However, when the temp drops below 0 deg I shut them off and switch to oil heat for zones not covered by the pellet stove. So I would not run them this Friday night.

Alan

[ishoot308]

Originally Posted by WinnisquamZ

Curious if anyone will be operating their mini spilts for heating this weekend. If so, please let us know how they perform in this weather


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We have used our hyper heat Mitsubishi in a large well insulated “efficiency apartment” over a garage. Last year in -10 degree weather it worked like a champ with no issue. It is the primary source of heat and at first I was skeptical….not anymore!

Will be using again this weekend and I will report back for you.

Dan

[FlyingScot]

Originally Posted by Slickcraft

Our hyper heat units 100% crossover efficiency is at about 0 deg F and they are good for operation down to minus 13 deg and 85% efficiency. However, when the temp drops below 0 deg I shut them off and switch to oil heat for zones not covered by the pellet stove. So I would not run them this Friday night.

Alan

I have never had mini splits in the same home as oil, so unable to do a direct comparison, but I am confused by your math or maybe by terminology. If mini splits are, say, 30% (or more) more efficient than oil, and they are operating at 85% efficiency at -13, aren't they still more efficient than oil at that temp? Thanks

[Slickcraft]

Originally Posted by FlyingScot

I have never had mini splits in the same home as oil, so unable to do a direct comparison, but I am confused by your math or maybe by terminology. If mini splits are, say, 30% (or more) more efficient than oil, and they are operating at 85% efficiency at -13, aren't they still more efficient than oil at that temp? Thanks

The math is straightforward. At minus 15 deg 85% efficient means 100 watts in gets only 85 watts of heat out. Over 0 deg temp the efficiency is over 100% so the heat pump puts out more watts than what is required to run the unit.

The above has nothing to do with comparison with oil heat. That said, the advantage over oil is temp dependent and numbers like 30% are on average. At 10 below zero best to run the oil burner.

Alan

[Descant]

With no direct experience, just quotes from vendors, I have the impression that as temperature drops, so does efficiency of the mini-splits. However, that says to me that they don't fail to heat, it just costs more to run them. If the temp drops to 0 F I pay more for oil and the electricity to pump the hot water or hot air around the house. Presumably, I pay more for the mini splits to operate as well, but I can turn down the heat in lesser used rooms and balance things out. Yes ? No?

[John Mercier]

I think it has to do with a drop in the BTU output to the point that the unit cannot keep up regardless of how long it runs.

[BroadHopper]

I know the efficiency of my condensing gas boiler and how much it cost per btu.
I also know the efficiency of my split system and how much it cost per btu.

The efficiency of the mini-split drops as the outside temperature drops. I find the cross-over point. This is where I switch to the more efficient heat.

Also, the gas boiler heats up a cold space rather quickly compared to the split system. So I use gas to increase the temperature and switch to the split.

An engineer told me that a split is inefficient when trying to raise the temperature of a cold home. It is efficient in maintaining a set temperature.

So do some research and use your judgment.

[TheProfessor]

I view so many new homes such as this.

With fancy dormers. With window bottoms so close to the roof.

Where do these architects think that the snow and melting snow is going to go?
Under dormer windows.

[WinnisquamZ]

Called my installer and asked about running my mini split in this cold. I have a 36k btu unit installed with 4 heads. Looking to run only one head. Kids are coming up for the hockey and we need to heat the space we close up for the winter months. I was told the performance will be cut in half, however with only one head running we should have no issues. Turned it on last evening and the space is holding at 62. About 800 sq feet


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[ishoot308]

Originally Posted by WinnisquamZ

Called my installer and asked about running my mini split in this cold. I have a 36k btu unit installed with 4 heads. Looking to run only one head. Kids are coming up for the hockey and we need to heat the space we close up for the winter months. I was told the performance will be cut in half, however with only one head running we should have no issues. Turned it on last evening and the space is holding at 62. About 800 sq feet


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Just curious if your split is a hyper heat unit or standard??

Dan

[WinnisquamZ]

Hyper heat, I believe. Good for -10 I was told


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[FlyingScot]

Originally Posted by Slickcraft

The math is straightforward. At minus 15 deg 85% efficient means 100 watts in gets only 85 watts of heat out. Over 0 deg temp the efficiency is over 100% so the heat pump puts out more watts than what is required to run the unit.

The above has nothing to do with comparison with oil heat. That said, the advantage over oil is temp dependent and numbers like 30% are on average. At 10 below zero best to run the oil burner.

Alan

Yes, this is why I am confused. I understand that a minisplit on warmer days is better than a minisplit on colder days. But the question is whether a minisplit on colder days is better than oil on colder days. If a minisplit is 30% better than oil in general, and oil is assumed to be always at 100% of its own efficiency, then doesn't the minisplit need to fall to 70% efficiency before oil is equal, and 69% before oil is more efficient? If all of this is the case, then the minisplit on a -13 day at 85% is still the best choice

[ishoot308]

Originally Posted by FlyingScot

Yes, this is why I am confused. I understand that a minisplit on warmer days is better than a minisplit on colder days. But the question is whether a minisplit on colder days is better than oil on colder days. If a minisplit is 30% better than oil in general, and oil is assumed to be always at 100% of its own efficiency, then doesn't the minisplit need to fall to 70% efficiency before oil is equal, and 69% before oil is more efficient? If all of this is the case, then the minisplit on a -13 day at 85% is still the best choice

Isn't the efficiency of an oil burner on average around 85%?? I realize some of the newer ones are better but for the most part 85% is pretty standard is it not?? Which would mean the mini split at -5 would be far more efficient would it not??

Dan

[John Mercier]

Originally Posted by ishoot308

Isn't the efficiency of an oil burner on average around 85%?? I realize some of the newer ones are better but for the most part 85% is pretty standard is it not?? Which would mean the mini split at -5 would be far more efficient would it not??

Dan

If it put out enough BTUs at the lower efficiency.

[DickR]

Originally Posted by Slickcraft

The math is straightforward. At minus 15 deg 85% efficient means 100 watts in gets only 85 watts of heat out. Over 0 deg temp the efficiency is over 100% so the heat pump puts out more watts than what is required to run the unit....

I think the term "efficiency" is being misused here (for a minisplit). The performance of a heat pump in heating mode generally is indicated by "Coefficient of Performance" (COP), that being the ratio of energy delivered inside (as heat) to energy input as electrical power (3412 BTU/hr per KW). A reasonable seasonal averaged COP might be around 3, but this will be substantially higher when the outside temerature is say in the 40s or 50s. The COP also drops as outside temperature drops. Think of it as being like pumping water uphill; for a given amount of pump power, you get a lower flow as you pump farther uphill.

That 85% number for the minisplit likely indicates how much of full rated capacity (BTU/hr) is being delivered from a very cold outside temperature. In general, except for some losses along the path, a heat pump delivers as heat all of the electrical energy input to the compressor plus whatever is absorbed from the source (outside air) by the evaporation of refrigerant on the cold (low pressure) side. Thus the COP will always be above 1.0 and substantially so.

It should be noted that heat pumps installed in heating climates generally are sized according to the expected heating load at some design minimum heat loss rate, which can be calculated sufficiently well for any house. On the other hand, most fired heat systems installed over the years typically are grossly oversized relative to expected demand, often by a factor of 2 to 4. Such a system has a lot of extra capacity, which leads to short cycling in normal use but which does let a cold house recover rapidly after a power outage or other period of deep setback. In contrast, a properly sized heat pump does not have that huge reserve of overcapacity for rapid recovery.

[Biggd]

My wood stove has been blasting out heat for two straight days now and I'm just able to keep the house at 68 degrees tonight, and it's a well insulated home. I have oil heat and I don't think that would keep up at these temperatures. I doubt a Mini Split would keep up tonight, it's -12 right now in Meredith.

[ishoot308]

Originally Posted by WinnisquamZ

Curious if anyone will be operating their mini spilts for heating this weekend. If so, please let us know how they perform in this weather


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As promised here ya go….12 below zero and still keeping up just fine. Approximately 1200 square foot apartment over garage. Mitsubishi hyper heat single zone mini split heat pump, (don’t remember the size). Impressive!

Dan

[WinnisquamZ]

Originally Posted by ishoot308

As promised here ya go….12 below zero and still keeping up just fine. Approximately 1200 square foot apartment over garage. Mitsubishi hyper heat single zone mini split heat pump, (don’t remember the size). Impressive!

Dan

Same here. Working great


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[John Mercier]

Good... that means that with any luck the store will be toasty warm when I get in tomorrow.

[WinnisquamZ]

As I have noted in the past. Mini spilts work when left on. Not great at recovery for either heat or ac


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[John Mercier]

They held the temperature at the Bristol store...
But the downstairs back up propane-fired heaters are going full bore.

[Biggd]

Originally Posted by ishoot308

As promised here ya go….12 below zero and still keeping up just fine. Approximately 1200 square foot apartment over garage. Mitsubishi hyper heat single zone mini split heat pump, (don’t remember the size). Impressive!

Dan

That's impressive! My house is about 1700 sq ft, lots of windows. With the sun shining in yesterday and the wood stove going full bore it got up to 76. Last night it dropped to 65 with the wood stove going full blast. I set the heat t-stat at 65 in case I didn't wake up to reload the stove.
I've been thinking of adding mini splits for AC and those days, in the high 40's & 50's, when it's not quite cold enough to light the stove.

[ishoot308]

Originally Posted by Biggd

That's impressive! My house is about 1700 sq ft, lots of windows. With the sun shining in yesterday and the wood stove going full bore it got up to 76. Last night it dropped to 65 with the wood stove going full blast. I set the heat t-stat at 65 in case I didn't wake up to reload the stove.
I've been thinking of adding mini splits for AC and those days, in the high 40's & 50's, when it's not quite cold enough to light the stove.

I will say that this living space above my garage is only a few years old and is very well insulated and I think that is obviously key.

I have mini splits out at my island camp also but not the hyper heat units just standard ones since I only use them for AC but they also kick butt in cooling down the camp on the hottest of days.


Dan

[joec]

I stayed up and monitored my Mitsubishi hyper heat heat pumps until 2AM last night and they performed well above my expectations. The specs on the heat pumps say the minimum temperature to make heat is -13. At 1:30AM, it was -17. The thermostat was set at 73 and maintained at 72 most of the day and dropped to 71, then 70 at 1:30 and stayed there. The house was 70 at 7AM this morning when it was -16.

The heat pump was a one to one 18,000 BTU unit that heated the entire downstairs, stairwell hall, upstairs hall and bath, about 850 square feet.

I have a second 3 head unit for each bedroom and heated only one bedroom last night with that and it did the job.

I have a propane stove in the living room as back up ready to go but it wasn't needed.

I had the dogs out at 1AM and those outside units were really working hard. The efficiency of the heat pumps were probably poor compared to oil or natural gas. The only other thing I noticed was the defrost cycles took a lot longer and it took longer for the heat to ramp back up. That was a little scary when the temperature got down below -14, but the heat pumps passed the test.

[DougNH]

Meredith about -17, Mitsubishi hyper heat, 5 heads, 42kBTU (2 years old). Monitored on the kumo cloud app from MA. This is for my 2nd floor, heads in 4 bedrooms and a large 40x20x10 room. Probably not a good comparison as the bedrooms open to a loft/great room and receives heat from the 1st floor which is oil boiler, hydro heat. I usually leave the 1st floor at 58 and 2nd floor at 60 but the heads in the bedrooms do not run much.

The large room (no heat from 1st floor) held 60 all night. As much as I like the system, I would have a backup plan. For us we have a propane wood stove in the large room.