Advice on mini-splits

[Wear More Layers]

Wear More Layers,

Are you heating with hot water baseboard or cast iron radiators? If you have CI radiators then heating to the low 60's with radiant is a LOT more comfortable than convection. MIni splits would require at least a few degrees warmer to achieve the same level of comfort as radiant but would be comparable with baseboard. Just curious.

As far as heating and cooling load calcs go, unless these guys or gals are taking lots of measurements all over your house(exterior ceilings, floors, walls, windows, doors, etc...) then they are just guessing.
A real heating/cooling load calculation is going to take a least a couple of hours

I don't think this is really needed though. Woodgeek's numbers with your prior oil usage look pretty sound to me and with mini splits it is safe to oversize up to about 1.5x. More than that and efficiency will start to drop as well as comfort. Undersized and you have the oil boiler to back you up if the mini splits come up short.

Noah

Thanks Noah. I do have cast iron radiators and didn't consider the difference with convection heat. The last thing I want to do is feel even colder than I already do.

t think you're right that everyone just guessed with their calculations because nobody took detailed measurements. If I go by Woodgeek's numbers, then I should aim for 26,000 Btus at a minimum. I've found the names of 3 more local companies that are listed on the Fujitsu site and will try reaching one or two tomorrow.

 

[woodgeek]

If I go by Woodgeek's numbers, then I should aim for 26,000 Btus at a minimum.

Rather than 'at a minimum', you should think 'diminishing returns' for systems larger than 26 kBTU/h.

 

[Wear More Layers]

Let's start over. You should def take a little time here.

Install cost:
If you bought a small minisplit, that provided X BTU/h and cost $Y installed and a bigger minisplit that also provided 2X BTU/h and cost 2Y, the smaller one will have a better payback because it would run all the time, while the bigger one might be idle sometimes (and thus not providing any value). So, the goal is different than with a furnace. With a furnace, you want to exceed your maximum demand so you never get cold. With a HP, the payback starts to suffer when the HP is oversized.

Frankly, I trust any demand calc based on usage more than any computer model done by a contractor. If your 450 gallons/year at your stated low temp is accurate, my estimate of 26 kBTU @ 70°F inside and 28°F outside is prob accurate to better than ±10%. The amount of oil you save annually is roughly proportional to the systems BTU/h output at 28°F for small units, but can't exceed 450 gallons no matter how large it is. By my estimate, a system that puts out 26 kBTU/h at 28°F would offset >80% of your oil usage. A single mini downstairs that puts out 18 kBTU might still cover 60-70% of your usage and cost half as much (and thus have better payback)

Since hot air rises, and the stack effect brings cold air from the bottom of the house I might skew the system to somewhat higher BTU/h downstairs. Maybe 18/12.

Operating cost:
On my side, I found that to a decent approximation, your operating efficiency is well approximated by that at your average January temp. You can look that up for your zipcode, but I would guess is is ~27-29°F. If Noah can find COP data for different models at that temp, you can convert those to costs per million BTU. Which unit puts out closer to nominal output at 5°F is irrelevant....you don't spend enough hours at 5°F for that to matter.

If your system offsets 350 gallons, it saves you $1200-1400 on oil. But at COP = 2.5 @ 28°F it would add $700 to your elec bill. If Noah finds a unit that works at 15% higher COP, that saves you $100/year. Compare that to the difference in install cost. In my case the lowest cost of ownership over 10 years was one step below the most eff unit.

This is frustrating, if your elec cost were <$0.15/kWh, the payback would be <6 years and it would be a no brainer. At 9 years payback, with some unpredictability in elec and oil prices, there is no rush to move. Do some internet research on kWh pricing options and/or call your utility. If you can get a lower rate, it will make the decision clearer.

Thanks Woodgeek. I've investigated elec rates and switched to the lowest cost provider in my area. Unfortunately, the overall kWh prices have little to do with the cost of generating electricity. Most of my bill is made up of distribution charges, fees, and taxes. (And people wonder why companies are fleeing the state of CT.)

When I call companies tomorrow, I will tell them that I'm thinking of 18 downstairs and a 9 or 12 upstairs.

 

[Wear More Layers]

Rather than 'at a minimum', you should think 'diminishing returns' for systems larger than 26 kBTU/h.

Good point. You know, Company #3 told me that the 12,000 Btu units are capable of 15,000 Btus each as long as both aren't ramped up to full speed at the same time. His point was that I'd be getting more than 24,000 Btus. II think I read somewhere that each could generate 14,400 Btus. So if 26 is the point of diminishing return, is Company 3 on target?

I gotta go to bed. My brain hurts.

 

[peakbagger]

minus 13 degrees at my house and the minis split is still running and putting out some heat. It locks out at minus 15 but I am impressed. Obviously the COP is darn low but more than 1, but the power is free from my net metering on solar.

 

[flyingcow]

The gentleman that installed mine was telling me that his was about -19 before it quit. He uses it all winter. Pellets and oil for back up.

 

[peakbagger]

After a bitter cold day (less than 10 F I think, the main floor of the house got cold away from the heat pump. Its still putting out heat but I expect the heat loss exceeds the heat pump output. I also noticed some ice buildup from snow that drifted on the coils. I think I will make some more robust snow shields around it one of these days.

 

[Wear More Layers]

minus 13 degrees at my house and the minis split is still running and putting out some heat. It locks out at minus 15 but I am impressed. Obviously the COP is darn low but more than 1, but the power is free from my net metering on solar.

What kind of mini split do you have?

 

[Seasoned Oak]

Why even try to push heat pumps at those temps. Is it not hard on the equipment to try to push heat pumps to make heat at sub-Zero temps? I would be firing up pellets or even oil at those temps.

 

[peakbagger]

Mitsubishi Hyper heat 1 ton..

With regards to "pushing" heat pumps, the unit is rated down to minus 15 and has a lockout when it hits that temperature and has a seven year guarantee on the compressor. I would expect that if there was a issue with using the equipment at low temps they would set the lock out at the point where this wasn't an issue. The reason for not running pellets or oil is that my power is essentially free based on a net metering surplus plus I don't have to feed pellets and scrape out a burn pot on occasion. I travel for work on occasion and would like an alternative to just running the house on oil at $3.40 per gallon.

 

[Seasoned Oak]

AS you said below -10 you dont have much choice.

 

[Wear More Layers]

I invited Company # 3 back to explain their calculations in person. He still comes up with needing no more than 24,000 Btu and offers a 1 year satisfaction guarantee on meeting my heating needs. Also, if I fear that I'm really not going to have enough heating capacity, I could upgrade from the original proposal to a slight larger set-up:
original -- 2 port external unit at 20,000 Btu; two 12,000 Btu indoor units = $6,300
alternative -- 3 port external unit at 24,000 Btu; one 15,000 Btu downstairs unit and one 12,000 Btu unit upstairs = $7,200

I also had a 4th company come out to give me estimates on Fujitsu units and am waiting on their proposal.

It appears that the $300 federal tax credit will go away on 12/31, so it looks as if I've lost out on some savings.

 

[Floydian]

Hi again Wear More Layers,

I've been meaning to comment on your situation. I'm concerned about your comfort level switching from CI rads to point source with warm air. I really think you will need to keep your air temp at least 4 or 5 warmer to achieve the same comfort you are used to now. Maybe not during mild temps but when it drops into the 20's during the day and colder at night you are going to feel the difference if you heat your house to 62. CI radiators offer a higher degree of comfort because they heat both the objects in your house as well as the air. MSHP's heat the air and you just don't get much heat transfer between warm air and cool objects.

That said I still think a MSHP could be a good fit for your situation, I just don't feel the MXZ-2B20NA is it. Again, it puts out 22,000 btu/h at 47 and 12,500 btu/h at 17. It would be nice to know the output at temps in between but I can't find that info. If we take a guess based on drop in output from 47 to 17, you could be looking at 18,900 btu/h at 37 and 15,600 btu/h at 27.
That is well short of the woodgeek's number of 26,300 btu/h at 28 and maybe worse still if you really do need 4 or 5 more degrees vs the CI rads.

As you may be forced to rely on oil in the colder temps regardless of what options you choose, I think I would be looking at a single unit installed in the lower level of the house to take a big bite out of the oil bill. Natural convection should allow enough warmth to make it upstairs assuming doors are open most of the time. With Mitsubishi, the MSZ-GE24NA would still give you more btu's at 27 vs the MXZ-2B20NA and it should cost less too. With Fujitsu the 15RLS2 could be a good fit at 18,000 btus all the way down to 5.
I would hope you could get either of the these units installed for under $5K, maybe even closer to 4k?

Obviously a unit like this installed downstairs does nothing to AC upstairs but a few hundred bucks on a window AC unit could solve that issue for not much money.

It's too bad that air to water heat pumps are not further along at this point. They are out there but prohibitively expensive. I look for this to change in the not so distant future.

Not sure I am really helping you in any way, sorry.

Noah

 

[peakbagger]

I agree with Flyodians observation. I normally keep my house at 66 when I am running baseboards, with the heat pump I tend to run a few degrees warmer. I have baseboard but not a lot of it as the house is well insulated so I don't have any real radiant . I don't know about 4 or 5 degrees but I ascribe some of it to the draft from the blower which is far more noticeable than the minor convective draft from baseboard. In general I think the heat pump tends to stratify the air more, its noticeably warmer near the ceiling and the difference between the ceiling and floor is noticeable. I also have learned not to set my heat pump back at night like I do baseboard.

Its all a learning curve. All I know is that the zone for my main floor is set at 58 degrees and generally above 10 degrees outside the main floor stays at 65 so the heat pump is contributing.

 

[Seasoned Oak]

Mitsubishi Hyper heat 1 ton..
With regards to "pushing" heat pumps, the unit is rated down to minus 15 and has a lockout when it hits that temperature and has a seven year guarantee on the compressor. I would expect that if there was a issue with using the equipment at low temps they would set the lock out at the point where this wasn't an issue. The reason for not running pellets or oil is that my power is essentially free based on a net metering surplus plus I don't have to feed pellets and scrape out a burn pot on occasion. I travel for work on occasion and would like an alternative to just running the house on oil at $3.40 per gallon.

WoW thats what i call a backup plan and a back up for the back up. Only weak link i can find here is a power outage,but im sure your prepared for that as well.

 

[Former Farmer]

I invited Company # 3 back to explain their calculations in person. He still comes up with needing no more than 24,000 Btu and offers a 1 year satisfaction guarantee on meeting my heating needs.

What temperature is he guaranteeing? If this does not meet your heating needs, what will he do? Will he install another system to meet your needs, all at his expense?

 

[peakbagger]

Backup plan if I am not home and the power goes out is homeowners insurance

 

[Wear More Layers]

What temperature is he guaranteeing? If this does not meet your heating needs, what will he do? Will he install another system to meet your needs, all at his expense?

He didn't mention what temp he'd guarantee. I'll have to ask. He did say that if the units don't keep the house at a desired temp, they company would install larger units.

 

[Wear More Layers]

Hi again Wear More Layers,
With Mitsubishi, the MSZ-GE24NA would still give you more btu's at 27 vs the MXZ-2B20NA and it should cost less too. With Fujitsu the 15RLS2 could be a good fit at 18,000 btus all the way down to 5.
I would hope you could get either of the these units installed for under $5K, maybe even closer to 4k?

Isn't MSZ-GE24NA an indoor unit and the MXZ-2B20NA an outdoor unit?

On Monday I'll be getting quotes from the company that sells Fujitsu units. I'll see what solution he comes up with.

 

[Floydian]

Isn't MSZ-GE24NA an indoor unit and the MXZ-2B20NA an outdoor unit?

Yeah, sorry about that. The outdoor unit for that is the MUZ-GE24NA.

I gotta run now but I'll post a little info on the Fujitsu's tomorrow.

Noah

 

[Wear More Layers]

I did some more reading on Mitsubishi and Fujitsu units. Here's what I picked up in tonight's leisure reading:

-- It appears that to get the highest HSPF, I have to purchase single port outdoor units. If I want a unit that has multiple ports, HSPF drops for Mitsubishi to 10.0 and Fujitsu to 9.8.

-- Both brands are comparable in price for multiport units, with Fujitsu just a little cheaper.

--Whereas a company would charge $6,800 for a 2 port unit plus 2 indoor units, the same items online cost about $2,900 with tax and shipping. Assuming additional materials plus labor adds $1,000 - $1,500 to the overall price, there's still another $2,400 - $2,900 in the mark-up. Purchasing these things online voids the warranty, but is the warranty really worth $2,900? Given how many websites are selling these things, people must find the savings to be worth the loss of warranty.

Could purchasing these heat pump thingies get any more complicated? Maybe I should just move south.

 

[Seasoned Oak]

THese companies should first have to determine if improper installation was the cause of failure before they can blanket void warranties. I think its just a money grab to just "assume " their product failed cuz it was installed wrong.

 

[flyingcow]

they won't cover the warranty unless put in by an authorized installer.

 

[DBoon]

Hi Wear More Layers,

You are seriously agonizing (likely without much benefit) about this.

Either the Mitsubishi HyperHeat or Fujitsu RLS2H High Heat models are what you want. You'll see them on-line for about half of what an installer will charge you. If the installer is charging you more than 2x the on-line price, you are being ripped off. Some will sell a 2x premium is a rip-off, but that is likely the lowest you will negotiate with a capable installer.

The Mitsubishi literature and documentation is terrible, and the Fujitsu is somewhat understandable, but both will tell you that the BTU ratings are for pretty low temperatures (i.e. 5 degrees F) and that you get much more heat from them at temperatures above that. Fujitsu and Mitsubishi rate their units differently, so don't go by model number alone. You might have to dig out the installers manuals to find this info, but I've already looked at both and these are comparable units.

Don't go with the multi-zone units. They are not as efficient and comparisons get complicated and prices get expensive with anything but the high-wall indoor unit.

Start slow with one single-zone unit downstairs. You will likely want a Mitsubishi 18k BTU unit or a Fujitsu 15RLS2. Sure, you won't have AC upstairs. Put in window unit for the 2 to 3 weeks a year you need AC up there. Then see how it works. You can always add one more mini-split upstairs later.

The first unit for ~$3500 will give you the biggest payback. Start with that first and see if you want another (upstairs) later.

 

[peakbagger]

One thing I learned is that installing a slanted roof over the unit for winter is a requirement. I had made a temporary 45 degree angle snow roof to keep snow off the coils on the back of the unit which ahs worked well but the overhang was too short on the front of the unit and therefore water dripped done the front of the unit and froze on the plastic grill on the front of the unit during the icing event that is occurring locally. I expect once I mod the roof to have more overhang it will be far less of an issue.

I and service techs I have talked to all recommend the single units and not the dual head units, due to the major efficiency difference and need for heat in cold weather. The rebate program I bought mine under was $900 rebate for a$1,600 unit, so it was definitely worth it for me. My theory stated previously is that based on what techs have told me, they rarely if ever see a unit fail except due to poor installation or external influences like physical damage to the unit. They rarely if ever fix the units, the just swap out the damaged unit. The outdoor unit which has most of the wear parts and most likely to get damaged can be bought separately so it highly unlikely you will have to buy the entire unit. Given the markup by installing dealers, I could buy an entire spare unit for less than their installed cost. Realistically, DIY is not real difficult, although it makes sense to hire a pro to do the lines if you dont have the specialized tools and the confidence. In theory the 7 year compressor guarantee is valid if you have a pro install, but the reality is that Mitsubishi has no system in place except its dealer network to make these repairs and it will be difficult to find a dealer that will honor a guarantee on a unit they did not install. I would expect they have some sort of cost split between Mitsubishi and the dealer on these repairs. The internet retailers can afford to sell them cheap as they have no need to have service network to honor guarantees beyond replacing a unit that was dead from the beginning.