Anyone added mini split heat pumps for supplemental heat? Did they save $$$?

I just did that. Had 2 window units and replaced with 3 wall mount 7K, 1 for each bedroom. Outside 24K, all Fujitsu.

Did it for the A/C but will be looking at how it helps the oil fired baseboard. It already helps for on demand heating in the room farthest from the stat.

I have a conventional split downstairs and wish I had installed a multi head minisplit system upstairs instead of my high velocity system. WOuld be a lot more efficient and I could zone it. 60% of the time it’s unoccupied and even we don’t use 2of the bedrooms unless we have guests. The other is a laundry room that’s all shaded after 10AM.

Below about 20-30F, when you add in defrost energy requirements, the boiler will be cheaper to operate. Above 30F, boiler standby losses are significant, so real delivery economy is lower than 82%, unless the boiler was installed in your living room... which for us steam nerds would be pretty cool.


The challenge with mini’s is very small rooms like bathrooms.

Ideal would be a air exchanger with a diverter When unoccupied it recirculates to a hallway dump zone, then a motion sensor turns on the outside air intake fan. Could have an entropy sensor and also act as an economizer. Wouldn’t be cheap but better than adding more indoor units.

I installed a COP 3 Mitsubishi 3 years ago to cool the downstairs (to old to wrestle the old 14k window rattler in and out of the window) I got the heat cool optionand it probably saves a couple of hundred a year because I use it when temperatures are the mid 30's or above. I've used it exclusively about half the time in the last 10 days

I give half that back for yearly service and if anything major goes wrong they are very expensive to fix. If you get one make sure it's a good brand and it's installed right - Daikin, Fujitsu and Mitsubishi.

Bob

We went with a 4 head Mitsubishi system, primarily for AC, but also for shoulder-season and supplemental heat.

We have an 82.1% efficient boiler for hot water heat and it does a great job at keeping the house warm, but we usually leave it set at 67 or 68. Having toddlers and infants, the wife likes keeping the kids rooms 70 all winter long and we were originally using portable space heaters to supplement so the whole house wasn't 70 degrees; the Mitsubishi mini splits solved that safety issue and likely more efficient too.

Overall, I have noticed they have decreased the gas bill some with the shoulder season use, but it's like running an air conditioner year round on the electric bill since the kids rooms need more heat. So instead of Paul getting the money, Peter gets the money.

We struggled deciding between the Hyper Heat model and the standard Mitsubishi heat pump. Since the overall 4-head system wouldn't provide enough BTUs for the whole house even at full capacity with Hyper Heat, we opted for the standard heat pump and saved 10%. Our thinking was the standard heat pump put out half of the overall system BTUs at 5 degrees and since we only needed supplemental heat in the two bedrooms with their smallest mini split heads, it was still more than adequate to provide the necessary heat - even at 5 degrees. While we felt confident in that decision during the summer, we are second guessing that now. The system put out the needed heat, but I wonder if the hyper heat system would have put out heat more efficiently as it got colder and have lowered our electric bill?

Someone on this site posted an excel spreadsheet recently for Heating Fuel Comparison Calculator. When I plugged in our numbers, running the mini splits, during shoulder season use, is roughly two dollars cheaper when comparing the Fuel Cost Per Million Btu (dollars).

Impossible to answer without you saying how much you pay for electric and your unknown existing fuel.

In my state of MA, at January 2022 prices, Natural Gas is cheapest. Oil is double natural gas. Propane and Heat Pump are equal at about 30% more than Oil. Resistance electric is double anything else as it has been ever since I was a little kid and that was all we had.

So Heat Pump is up there with Propane as one of the expensive ways to heat.

As a old HVAC guy who learned to hate air to air HPs back in the 70s and 80s. The mini splits are much improved, I installed a Mitsubishi Hi 2 on my back porch, regardless of what you hear it struggles below say 10 Deg F and mine does not have back up. Does a wonderful job 10 degrees plus and on AC.

But my indoor fan blower wheel in spite of regular cleaning of the thin, nearly useless OEM filter was packed, Packed full of dirt and other on the wheel fins. I cleaned with high pressure compressed air and then needed to clean the porch ! Yes they sell Bib kits with a sprayer to clean and for next time I have a canister filled with soapy water, power with compressed air, sprayer.

So complex and expensive to repair IF you have issues, and the multi head units can be a nightmare to service. Regardless they are a 200% improvement over the ones I had to service and hear the complaints about in the 1970s and 80s. I rarely worked on residential most were commercial units.

I am trying a filter coat spray on my filters to see if that will help reduce the cleaning of the unit.
Just one link to a Bib Kit >https://www.speedclean.com/product/mini-split-bib-kit-xl/

Here is the Fuel Cost calculator stolen from the State of Maine website:

Heat pump is 30% more expensive than oil? Something’s wrong with that heat pump.

ethicalpaul said:

Heat pump is 30% more expensive than oil? Something’s wrong with that heat pump.

Oil twice the cost of NG is also questionable!

Someone needs to check the BTU per therm, gal and KW

wmgeorge said:

I pay 9 cents per kWh, some here pay 22 cents, it all depends on the cost per Btu. The calculator I posted above does that for you.

What about all the other fees that are added on per KW?

My electric cost averages $0.10 to $0.12 per kwh depending on time of year and how much we use. That is total bill divided by total kwh, so inclusive of all fees. We have a 2 ton minisplit that we purchased mainly for AC, but I have found it to be very economical for heating the house in the fall and spring. With current oil prices the minisplit costs about half as much to run.

wmgeorge said:

pecmsg said:

wmgeorge said:

I pay 9 cents per kWh, some here pay 22 cents, it all depends on the cost per Btu. The calculator I posted above does that for you.

What about all the other fees that are added on per KW?

All the fees are included, Mid American gets most of its power from wind generation.
Nat gas cost is way out of line considering its basically a burn off or surplus from oil drilling. Oil has always been expensive it seems.

then you must have the cheapest electric rates in the country!

jlonj said:

I’m considering installing mini splits, mostly for air conditioning, but I like the idea of using them for heat during the shoulder seasons. I’ll actually probably get the hyper-heat models just as a backup if my boiler ever breaks down, but I have a pretty new Weil McClain EG65 82% steam boiler, so I’m not super worried about that.

But I want to understand energy savings before I pull the trigger. I’ve read these heat pumps are much more efficient in above freezing conditions, but I’m having trouble actually figuring out what savings I can expect. Is it like $500/year? Or like $50/year? Because obviously the former would make me pull the trigger faster.

Thanks!

I have many customers here in central PA who have similar systems. What you’re describing makes the heat pump the primary and the steam would be the secondary or back up for use as needed in the case the heat pump does not meet demand. The answer to your question involves quite a few variables but essentially it’s going to be a great idea if you live in a cold climate. Your situation will be unique but ALL of my customers have reported they were shocked how much money they saved by using Hyper Heat Mitsubishi units for the majority of the heating season. Most of them have heating oil hydronic systems and a few NG and most are older homes (1950’s or older). Hope that helps. Just my observations. Good luck. 

The heat pump will save you money on the shoulder season days. You won't have the big boiler and associated pipes heating up just to bump the indoor temps up 10-20 degrees. The breakpoint where you are better off with steam will vary based on local energy prices.

Making any kind of generalization about energy costs and energy savings is just plain wrong, and can be very misleading to less well informed people who happen to read the article or the post on the Wall. Just plain don't do it -- it's bad enough when some talking head "expert" expounds on it.

Each individual situation -- building by building -- must be considered individually.

I wish I had your electricity rates, @wmgeorge . Where we are it's more like 25 cents per KWh (about $7 per 100,000 BTU) -- and scheduled to go up in the near future. Natural gas isn't obtainable at all. Oil is about $2 per 100,000 BTU (bulk buy -- spot market is around $3, but wildly variable).

Jamie Hall said:

I wish I had your electricity rates, @wmgeorge . Where we are it's more like 25 cents per KWh (about $7 per 100,000 BTU) -- and scheduled to go up in the near future. Natural gas isn't obtainable at all. Oil is about $2 per 100,000 BTU (bulk buy -- spot market is around $3, but wildly variable).

I think that is the winter rate, never paid any attention before. I did the breakdown for my son who runs a 96% gas (I do not know the exact %) HW boiler and it also does his DHW. I said according to my calculations its cheaper this year to run Mini's, he said not. According to this he would save $4 per using the Mini's. He had the money when he built, should have gone geothermal.

But... Mini splits are suppose to last 8-10 years If you go that route. Geothermal since its All inside tend to have less service problems, once the start up is completed. Geo tends to have stable COP because ground temps don't change that much. So its going be interesting. 

It you pay 8 cents for power then heat pump is cheapest. 

@wmgeorge can you elaborate some? SEER is irrelevant to heating and having installed a ducted minisplit, it wasn’t expensive. Not important anyway if the decision comes down to ground source or air-source, since an air handler is being installed either way. I agree geothermal can be more efficient (sometimes), I challenge that it’s worth the cost of the drilling. 

SEER is just cooling and is confusingly named, probably because AC came first. I agree geothermal could be potentially easier to repair. I don’t think homeowners care.