Advice on mini-splits

[Wear More Layers]

Hi. I was investigating pellet stoves and wood stoves as an alternative to oil heat when members of the Hearth Room brought mini-split heat pumps to my attention. I did a little homework and had 3 companies come out to give me estimates. Their solutions and prices are so different from one another that I don't know where to turn next. Below are details:

my home: 1,300 sq ft, 2 story, built in 1950s

Company #1 solution: 2 downstairs units + 2 upstairs (1 per bedroom); total of 36,000 Btus; cost = $12,350 after $250 utility company rebate; ineligible for tax credit

Company # 2 solution: 1 downstairs + 2 upstairs (1 per bedroom); total of 42,000 Btus; cost = $9,300; ineligible for utility company rebate or tax credit

Company #3 solution: 1 downstairs + 1 upstairs (in hallway pointing at bedrooms); total of 24,000 Btus; cost = $6,300 after $250 utility rebate and $300 tax credit

Each company uses Mitsubishi units, and each is charging me ~$3,100/unit after rebates/tax credits. How many units and how many Btus do I really need? Are the prices reasonable? If you have advice, I'd love to hear from you.

 

[DBoon]

Hi Wear More Layers, welcome to the site.

I just put in a Fujitsu mini-split. I had Mitsubishi units quoted as well, but they were priced higher by the installers around my parts.

It would be hard to estimate your BTU needs from the info you provided. Can you provide more info about your house? How much insulation in the attic and walls? How good are your windows? Does your home feel drafty? How much oil did you burn last year and what temperature do you keep your house?

Also, if you have few people in your house and the doors are mostly open to the rooms, you might find that company #3 solution is the right way to go, provided your heating needs aren't too high. Heat will travel. You can always add more later. You might even want to start with just one downstairs for the moment and see how that works for you - at the very least, it will reduce your oil consumption a great deal, and you can add more later.

 

[begreen]

The first thing to do is look at your old heating bills. Go back at least a few years. Take the total heating fuel consumption from Dec thru Jan. for each year, then average these numbers. Now divide that number by 62, then by 24. That will give you an average fuel consumption per hour during winter. Then convert that consumption to btus by mulitplying gallons of oil or therms of gas times the corresponding amount of btus in that fuel. That will provide the average btus per hour your house uses in winter.

Other things to check. Are they installing Mitsubishi Hyper Heat units? That is what you'll want in CT. But they are only available in single head units. It could be that you choose plan #3, but by the heat calcs come up with needing a larger downstairs unit. Whether one or two is better will depend on how open the floorplan is downstairs. If it is not open it may take two units or a dual-head unit. Upstairs is a bit harder to call. Are the bedroom doors normally left open or closed? If open, a hallway unit could be fine. If not, a head unit in each bedroom may work out better.

 

[peakbagger]

Single unit Mitsubishi Hyper heats are $1,600 on ebay with about $200 to $300 other installation accessories (tubing and plastic gutter to cover the tubing). I built my own support rack so that would be additional (I would guess $50). I had a breaker and wiring. So the installer is receiving $1100 for installation time. I expect with the right tools a tech and a helper can do an install in 4 hour average (more for second story and less for 1st floor). I would ask if they are doing the wiring or if that is separate as most hvac techs don't have electricians licenses. I don't know why but Mitisubishi doesn't make a hyper heat unit dual head and my understanding is dul head units don't have the low temperature efficiency.

One thing to keep in mind is that few folks would have 8 breaker spaces in their house electrical panel. If your panel is rated for split breakers you may get away needed in 4 full size. There is a good chance that you may have put in subpanel if you have a 200 amp panel and if you have a 100 amp service, you probably need an upgrade to 200 amp. This could add $1 to 2K to the project.

 

[DBoon]

Are they installing Mitsubishi Hyper Heat units? That is what you'll want in CT.

I would second the advice the get the Mitsubishi hyper heat units. I got the Fujitsu equivalent, and they do a great job of putting the heat out even at ridiculously low temperatures.

 

[Wear More Layers]

I would second the advice the get the Mitsubishi hyper heat units. I got the Fujitsu equivalent, and they do a great job of putting the heat out even at ridiculously low temperatures.

None of the 3 companies recommended Hyper Heat units. Someone else on hearth.com in the Hearth Room told me I didn't need Hyper Heat given my location in southern CT. I'm ok with kicking the oil heat on at very low temps because it will cost less to do that than to buy separate outdoor units for each Hyper Heat installation.

I don't have the skills necessary to install the units myself; hence the need to find a company to do it for me. I did consider purchasing everything online, but Mitsubishi and Fujitsu apparently don't offer warranties on web purchases.

All of the companies looked at my electric panel and indicated that their electricians could handle the job without issue.

As for heat use in my house: the windows were installed within the past 15 years and are doubel-paned. The walls are insulated, but I don't know how well. The attic is insulated but not ideally. Energy auditors tried sealing as many small leaks in the house as they could find, and I don't feel any drafts in winter.

I keep the house cool (mid-50s) during the day and "crank" it to 58 at night. That's frankly just a tad too cold for me. I'd like it to be in the low 60s. The downstairs is fairly open, and two of the three companies thought that one strategically placed unit could heat the whole 1st floor. The upstairs has 2 bedrooms plus an office and bath. I keep all of the doors open, which is why one company thought a hallway unit could heat everything. The other companies thought that at least the master bedroom needed its own unit.

I'm too tired to do math at the moment and will run the numbers suggested by begreen tomorrow.

Thanks for everyone's helpful comments.

 

[woodgeek]

I suspect the installers, in addition to wanting to sell you as much hardware as possible, do NOT want you to call back and complain that you don't have enough BTUs. You still have the oil backup system to 'top off' the heat on very cold days (you would set the oil stat a couple deg below the minis, and it would only come on when the minis were wallowing).

Yeah. Bottom line is that HPs or minis cost a lot per BTU capacity. Even more for Hyper-Heat. With a furnace, a slightly bigger burner is a small upcharge, so you oversize with a safety factor with a demand based on square footage or other estimates. With a HP, you do not want to pay for too much capacity.

If money was very tight (doesn't sound like this is the case), I would install 1 downstairs. It would take a big bite out of oil/wood usage, would carry the house in the shoulder seasons (if natural circ upstairs was not an issue) and would have good payback.

If money was not super tight I would do two units, one up one down. You get some zonal heat/AC control (I wish I had that with my 1 zone system) and more heat overall. More than 2 sounds kinda nuts to me.....I think those installers are worried about distribution, and you have addressed that and are not concerned.

Now to get technical......

1. let's figure out what your **average** BTU/h load is during January. If that is 24 kBTU/h, then Plan 3 is prob a good fit. If it is 36, then I would still prob go with installer #3 (I like his logic), but talk to him about getting bigger units (there are many sizes). Installation on bigger units will prob be the same as on smaller units (bigger units will give you more BTU/$$ installed)
2. get the specific part numbers the installer intends, and I will try to look up detailed specs. The '12k BTU' size mini that is a nominal value that depends on outside temp. We can look up performance tables and verify that is will provide the BTUs you need at average Jan temps.
3. Send $$/kWh from your utility and I will estimate savings/ROI.

PS: The folks pushing the '100% heating capacity at XX°F' are in my opinion selling snake oil. All HPs run on refrigerant, and the volatility (vapor pressure) of the refrigerant goes down with decreasing temp, so the BTU/h goes down too. This is not a design flaw for HPs, it is physical chemistry. The units that 'deliver 100%' down to some temp are just being throttled down above that temp. Duh. All you care about it that the BTUs delivered on an average Jan day meet your needs. All minis will throttle down above that (which is nice, since they will run quieter and more eff then). The Hyper Heat units are nice, and if I lived North of Boston climate-wise, I would research them. If you are in the lowlands in southern CT, with a roughly NYC climate, you don't need to go there.

 

[Justin M]

If you keep the doors open and you like it cool anyway you will be fine with 2 units. They take a while to recover, so you wouldn't want to do too big of a set back during the day. It's more of a set it and forget it thing, but they are cheap to run so that's not a big deal. On my Mitsubishi multi-unit setup there is a minimum heat set point of 68°. If I set it to anything lower it will still heat to 68°. I'm not sure why they would design it that way. So that's one other thing to look in to since you like it cool.

 

[woodgeek]

OK, found the other thread..... https://www.hearth.com/talk/threads/head-spinning-pellet-or-wood.117232/page-4#post-1577722

we already estimated cost per MMBTU.

You say you use <600 gals/year and keep the stat at more like 58° than (typical) 70°F. We need to estimate your demand at something warmer, like 68-70°F.

If your climate is 5000 heating degree days (HDD) like NYC, that assumes a stat setting of 70°F and a 'base temp' of 65°F. (other heat source like appliances, body heat and passive solar would heat your house 5°F above outside temps). Your base temp is prob more like 53°F rather than 65, so you are saving 12 HDD's per day * 150 heating days = 1800 HDDs, so maybe your usage is 1800/5000 = 36% lower than it would have been with a 70° setpoint.

Estimated another way...each degree you setback saves you 1% for an 8 hour setback, or 3% for a 24 hour setback (rule of thumb). You are setting down 12°F, so you are saving 36% by wearing long-johns and a sweater.

So, I still need more info....are you running that oil heater over the summer, and are you using it for hot water?? If the answer to both is yes, then you are likely using 150 gallons for DHW and summer standby, and only 450 gallons for heat. If you have a elec water heater and shut the oil off in the summer, then you are using 600 gallons for heat. This is a 25% uncertainty. I will do both cases.

Case 1: 450 gallons for 58°F stat setpoint.... at 70°F setpoint, this would be 450/0.63 = 714 gallons = 75 MMBTU for 5000 HDD (base 65). This means your demand is 15000 BTU/HDD. On a January day when the average temp was 28°F, that is 42 HDDs or 15000*42/24(hrs/day) = 26.3 kBTU/h @ 28°F outside.

Case 2: Same calculation, but assume 600 gallons: Final figure is 26.3 * 600/450 = 35 kBTU/h @ 28°F outside.

So, if the 600 gallons includes summer standby and DHW, then your 3rd quote system (if the nominal BTUs are accurate) will be able to carry your house down to 29-30°F, and likely carry 80+% of your total seasonal heating needs.

In the other case, your oil system will need to help out whenever the temp outside gets below ~40°F or so. This would still save enough money (>50% of your oil usage at 70°F stat setting) to make things worthwhile. I would still go with 2 minis, but try to upsize one or both to get closer to 36 kBTU nominal at 25°F. Of course, if the installer could get you three 12 k minis installed for the price of 2 18k minis, that would be great (but I think that unlikely).

 

[flyingcow]

I have 2 mitsu hyper's. An 18kbtu down stairs and a 12kbtu upstairs. The 18 kicks out some serious heat. I have a 2 story/1800sqft house on a hill in northern maine. Avg insulation. I was going to put a 9k in the upstairs, but the cost was the same as a 12k unit. And they performed equally. When we use the 18k unit, we leave the doors open upstairs(the upstairs HP is turned off). If I set the unit at 70f and it's 20f outside, leave it alone for the day, it heats the whole house pretty damn easy. My guess is a 12k unit would have done the job too.

I also think you might want to try one downstairs, then do the upstairs unit later. Also, if you're keeping your house at a "high" of 58, any more of a setback during the day might not help.

Look at the specs of these units. Find out how low you can put your heat settings. My 18k unit only goes down to 68 or 70f. I called Mitsu directly with a few questions. Very easy to talk to and took the time to answer my questions. It's worth your time to call them directly. They have very good customer service.

This is what Mitsu gave me for energy consumption of my 18k unit.

Cooling mode uses 1270 watts
Heating mode outside air at 47f uses 1540 watts
heating mode outside air at 17f uses 2620 watts.

 

[woodgeek]

Great advice....having the bigger unit downstairs makes good sense since warm air rises. You will want the AC function upstairs, but the BTU load in AC will be a lot lower.

 

[Wear More Layers]

I don't use heat from April to early November, but I do use oil year-round for hot water, so I think Case 1 from wood geek is a more accurate estimate.

The company that suggested 2 units proposed:
MXZ-2B20NA 2 port outdoor unit
MSZ-GE12NA indoor unit, one on each floor

The company that suggest 3 units proposed:
MXZ4B36NA-1 outdoor unit
MSZ-GE24NA indoor unit downstairs
MSZ-GE09NA-8 in each upstairs bedroom.

My cost for electricity is $.182/kWh.

 

[woodgeek]

Ok. Took a quick look at specs. I didn't find any real detailed info.

The quoted 2 zone system has one outdoor unit and 2 indoor units.

A selection guide can be found here....
http://www.mitsubishicomfort.com/en...ons/product-showcase/outdoor-multi-zone-units

It suggests that the quoted system maxes out at 22 kBTU/h, which is a bit short of the estimated 26 kBTU/h loss at typical Jan average temps (28°C) estimated above.

What if you wanted to upsize?
You could upsize the outdoor unit from the MXZ-2B20NA to the MXZ-3B24NA, the 'next size up'.
The latter unit (see link above) claims output up to 34 kBTU/h, above your Jan demand.

The quoted system looks like $2790 for the hardware....
https://www.acwholesalers.com/Mitsu...ump/19673.ac?gclid=CPGsu626oLsCFYQ7OgodnCYAeQ
The upsize system is $3600
https://www.acwholesalers.com/Mitsu...-Pump/19715.ac?catId=cat1034&mainCat=&subCat=
If we assume the install and lineset is the same price, this is a roughly $800-$1k upgrade to get a system that nominally puts out 50% more BTUs.

we need to be careful with nominal numbers....actual output will be lower than peak output by 10-20% due to defrost cycling....Are these numbers including defrost losses (I would guess not). At what temp is the nominal output achieved? Couldn't find that out, but probably around freezing (ok for our calculation). But this argues towards having a little margin. Maybe your installer knows?

Now, the quoted 2-ton system would def take a big bite out of your oil consumption and would likely carry you whenever the weather was above freezing, but it would need the oil to help out otherwise. Of course, even in cold weather it would be supplying 70-80% of your needs, so it would still saving you oil then.
In comparison the upsize system might be able to carry you solo 90% of the time. During milder weather it would run slightly more efficient and quieter.

A few issues....
--I suspect the smaller system + oil would be more comfortable. As optimistic as you are about distribution, the perimeter of your house will get cold during cold weather. Putting 10-20% of your BTU into the baseboards won't cost a lot, but will even out that cold perimeter nicely.
--The oil system has standby losses of 2-3 kBTU/h whether it circulates or not. That will help the smaller system to carry to lower temps w/o circulation.
--if you were planning on ditching the oil system at some point in the coming years (i.e. it is old, you don't like the DHW service), then you would be in for a cost down the road of a elec water heater (which by saving you oil standby would be cheaper to operate despite your spendy elec) and some sort of backup for the minis, either new elec baseboards, or better, an 'elec boiler' with your existing baseboards. That would cost more per BTU than your existing mini_oil setup, but if the mini was powerful enough, the need for backup would be negligible cost. If you are hating the oil, get the upsized system.
--If you are planning some sig energy audit/ energy eff upgrades to your house, the smaller system might make more sense. It will save a ton of oil right from the start, and will be 'right sized' for a future better sealed version of your house. Such an audit will help with the distribution/comfort issue.
--You need to contact you utility to see if you can get cheaper elec in the winter as a heating customer. I didn't do this until after I installed my HP. Turns out I got a 50% discount (!). That is phased out now, but you will wnat to know one way or another.

--Couldn't find out about the min setpoinf of 68°F. That would tick me off, ask your installer.

 

[woodgeek]

Ok. After a little more consideration, I have to say it comes down to your future plans and current desires. You can def get a system that saves oil, and whether you knock down the oil 70% or 85% doesn't really matter as far as the decision is concerned. More important is comfort and future options. I am not worried about your open plan downstairs, but I am more worried about your bedrooms upstairs. Maybe you are happy leaving the doors open, but that could change in the future to become an issue. If you will be keeping the oil system forever, the baseboards will prob keep everything nice and even. Go with Company 3 (as quoted or upsize).

But if you hope to get rid of the oil, then the company 3 option might force elec baseboards or elec boiler options in the future, whereas having two heads upstairs might avoid that issue all together. I might want a three head system, one big downstairs, one small in each upstairs bedroom, total nom BTU > 30 kBTU.

Think about your future plans, and talk to your installers some more.....

--At $0.18/kWr, your cost per BTU will be equivalent to ~$2.25/gallon oil (10% better than that in warm weather, worse in cold weather). If you can buy oil at $3.50/gal discount, this whole shebang will only save you $1.25*550 gal = $700/year. (assuming higher usage from a 65° setpoint)
--That is a ~9 year payback on the cheapest option, assuming oil and elec stay the same price. If you get a elec discount for heating, this changes big in your favor. If oil gets cheaper by 30% next year, you lose.
--Changing your DHW service over to elec or a HPWH could save you 150 gallons outright (if your boiler could get shutdown in the summer), saving you several hundred dollars a year net. This might have a better payback than the minis, depending on the cost of plumber.

 

[Dave A.]

PS: The folks pushing the '100% heating capacity at XX°F' are in my opinion selling snake oil. All HPs run on refrigerant, and the volatility (vapor pressure) of the refrigerant goes down with decreasing temp, so the BTU/h goes down too. This is not a design flaw for HPs, it is physical chemistry. The units that 'deliver 100%' down to some temp are just being throttled down above that temp. Duh. All you care about it that the BTUs delivered on an average Jan day meet your needs. All minis will throttle down above that (which is nice, since they will run quieter and more eff then). The Hyper Heat units are nice, and if I lived North of Boston climate-wise, I would research them. If you are in the lowlands in southern CT, with a roughly NYC climate, you don't need to go there.

Not sure where you're coming from here. First they're snake oil, then they're good in colder climates. No personal axe to grind with respect to the Hyperheats, don't even own one. But I do like the specs compared to other heat pumps. Most heat pumps significantly drop their BTU heat output as the outside temps drop and the temp of the heated air drops as well. Is that really what you want in a heating system. Not sure what changes Mitsubishi makes with the Hyperheats that allows a more user friendly heat pump system than others but it does sound (to me) like the direction the industry should be going.

We can get 5F temps here in this climate and a heat pump that works without requiring backup to 5F sounds pretty good to me. Electric backup has been the dirty little secret about heat pumps that's given them a bad name making people think they are inherently expensive to run. The resistance electric is automatically turned on at almost every opportunity (unless you work it out with your installer to set up the system otherwise) driving the utility costs up without the user even being aware of it. It's turned on during defrost cycles, turned on whenever the thermostat is turned back up to more than a degree or so above the current inside temp and turned on below certain outside temps. Although the heat pump may be still making minor contributions, most of the energy use is generated by the resistance heating at these times.

The hyperheat avoids all that, it's pure heat pump. What's wrong with that.

 

[woodgeek]

I just don't like downtalking the capabilities of other systems in milder climates (I think that is overstated).

No personal opinion about HyperHeats whatsoever. I just think that properly installed HPs of modern vintage are aok as far north as southern New England. Beyond that, it seems a lot of folks are happy with the their HyperHeats. I'm cool with that. I just stop short of folks saying that its HyperHeat or no go, and describing bad installs or systems from 20 years ago. I've got a cheapo 4-ton mid-range Goodman brand HP heating my house for $700/yr, and my climate is basically a match for NYC/southwestern CT.

I think HPs will revolutionize heating in New England, and are a possible solution for lots of folks stuck on Heating Oil. The glass is full, there are many systems that will work in southern NE, and at least one (HyperHeat) that works well in the North.

 

[Wear More Layers]

Everyone has given me a lot to think about. My head is going to explode. My latest completely unorganized thoughts that I'm trying to tie together include:

-My goal is to save money to heat my house into the low 60s (though if the splits bring it to 68, I'll live). Recouping $700/yr is lower than I had hoped, but I see that the ridiculously high elec rates in CT contribute to this reality.

-I don't have central air conditioning, and with a ductless home, estimates for installing traditional AC on both floors run from $7,500 up. I was even looking at mini-splits in the dog days of summer last year but didn't bite. (At that time I didn't know some of them provided both heat and cooling.) Getting AC as part of the deal makes the $700/yr return on my investment more palatable.

-I don't know what the future holds but expect that if a bedroom down the road needs a door closed for extended periods, a small space heater could solve the problem if it got cold and the oil heat didn't kick on.

-I don't plan to get rid of my oil boiler. With a pricy hot water tank running from it plus a new oil tank, both installed within the past 5-6 years, I'm wedded to oil at least for DHW for the foreseeable future.

In sum, knowing that it will be hard for me to go completely oil-free, I don't think it's worth spending over $9,000 on HPs at this time. I will call Company 3 and double-check whether they think they've sized the units properly. I'll also call Company 2 to see if they'll reconsider installing 1 bigger unit upstairs instead of 2 smaller ones.

As for regular HP vs. Hyper Heat, none of the 3 companies recommended Hyper Heat. I don't know if it's because they didn't think it gets cold enough here or because they knew the cost would be too great. Does anyone know the price difference between regular Mitsubishi's and Hyper Heat versions?

 

[velvetfoot]

I think HPs will revolutionize heating in New England

Watch electric prices go up then, lol.

 

[flyingcow]

Wear More Layers- My hypers were $600 more than a regular HP. My utility company was offering a $600 rebate, just on the hypers. But, it may have changed since this summer. Wouldn't hurt to check. It cost me a just a shade over $4k for my downstairs 18kbtu unit. I have it running now, it's 15f outside temp. Purring like a kitten. The variable speed compressors and fans are whats making these units favorable to the northern climate.

FWIW, i have a gassification wood boiler. prettty damn efficient in it's own right. On the back of an envelope figuring, the HP is on par( if not cheaper) for heat. Once I get a meter hooked up to HP, i will be able to get real numbers for my cost. I'm using the HP for heat during the day and running the wood boiler for DHW and radiant floor in my kitchen. I'm using significantly less wood playing with my new toy. It's supposed to be zero or below zero later this week. Might play with the HP and see whats happens. But I'll pretty much be back into the wood boiler 24hrs a day at those temps.

 

[Wear More Layers]

Wear More Layers- My hypers were $600 more than a regular HP. My utility company was offering a $600 rebate, just on the hypers. But, it may have changed since this summer. Wouldn't hurt to check. It cost me a just a shade over $4k for my downstairs 18kbtu unit. I have it running now, it's 15f outside temp. Purring like a kitten. The variable speed compressors and fans are whats making these units favorable to the northern climate.

FWIW, i have a gassification wood boiler. prettty damn efficient in it's own right. On the back of an envelope figuring, the HP is on par( if not cheaper) for heat. Once I get a meter hooked up to HP, i will be able to get real numbers for my cost. I'm using the HP for heat during the day and running the wood boiler for DHW and radiant floor in my kitchen. I'm using significantly less wood playing with my new toy. It's supposed to be zero or below zero later this week. Might play with the HP and see whats happens. But I'll pretty much be back into the wood boiler 24hrs a day at those temps.

Thanks flying cow. I'll see what prices my local companies give for hyper heats. How do you keep your outdoor unit free of snow up in Maine?

 

[flyingcow]

Thanks flying cow. I'll see what prices my local companies give for hyper heats. How do you keep your outdoor unit free of snow up in Maine?

It's mounted on the wall of the house, up high enough not to bother. But we'll see, this is my first winter with it.

 

[Wear More Layers]

It's mounted on the wall of the house, up high enough not to bother. But we'll see, this is my first winter with it.

None of the companies I talked to offered this solution. After bigger storms I would have to go outside and shovel the snow from the unit, which would sit on a concrete pad at ground level. Maybe I can convince them to elevate it atop pressure-treated lumber or concrete pavers to buy me at least a little extra clearance.

 

[woodgeek]

None of the companies I talked to offered this solution. After bigger storms I would have to go outside and shovel the snow from the unit, which would sit on a concrete pad at ground level. Maybe I can convince them to elevate it atop pressure-treated lumber or concrete pavers to buy me at least a little extra clearance.

That is pretty unacceptable IMO. I have my unit of 12" plastic legs called 'pump ups' and I seldom get more than 12" of snow. Imagine going to bed with the blizzard coming....no fun.

 

[Justin M]

How do you keep your outdoor unit free of snow up in Maine?

Mine is mounted on a metal stand on top of the pad that keeps it about 18" off the ground.

 

[woodgeek]

You could build (or pay a handyman to build) a couple 18" platforms out of pressure treated....I skipped the concrete pad, an just built a level frame of pressure treated, filled it with dirt and put a plastic pump pad on top. That and the legs.