Advice on mini-splits

[altmartion]

did any of these contractors do a load calc? with mini splits it is crucial. they don't have the dehumidifying capacity as a normal ducted system would. so it needs to be sized right.

 

[flyingcow]

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.

Both units are on a wall hanger supplied my Mitsu. Pretty slick set up. Yrs ago i used ti install comm HVAC equipment. This bracket system is pretty slick. But There is a slight vibration coming thru from the outside wall. especially in the heat mode. I have my downstairs unit on outside wall. maybe 3ft up? The upsatirs unit is about 18ft high. Both on the hangers supplied by Mitsu.

No pics, but this is one of the FAQ'a
http://www.mitsubishipro.com/en/professional/resources-and-tools/faqs

 

[flyingcow]

Not a great pic, not sure what will happen when you click on it

 

[peakbagger]

I built my own hanger out of spare unistrut and haven't noticed any extra noise on the interior. I also made a removable frame with a slant roof over the top of the heat pump that bolts to the hanger and the wall. The unit sits about 4' off the ground. Its near a driveway so I don't have room to plant a cedar in front of it. In addition to the mini split I have to have wall mounted disconnect and I also used the plastic gutter to route the control wire, condensate drain and refrigerant tubing. I have cedar siding so everthing in contact with wood is either stainless or coated fasteners.

 

[Justin M]

Here is mine.

 

[Dave A.]

But There is a slight vibration coming thru from the outside wall. especially in the heat mode.

Wondered about that. Kind of going full circle -- get a mini split to get rid of the window shaker aspect of window/wall units, then hang the outside unit on the wall and end up back where you started.

 

[flyingcow]

Wondered about that. Kind of going full circle -- get a mini split to get rid of the window shaker aspect of window/wall units, then hang the outside unit on the wall and end up back where you started.

It's a pretty minor vibra/noise. The house has to be dead quiet to hear it.

 

[altmartion]

It's a pretty minor vibra/noise. The house has to be dead quiet to hear it.

is it the unit itself or the refer line vibrating? it is common for the line to vibrate.

 

[Wear More Layers]

did any of these contractors do a load calc? with mini splits it is crucial. they don't have the dehumidifying capacity as a normal ducted system would. so it needs to be sized right.

All 3 companies did load calculations, which is why I was surprised by their very different conclusions. I called Company 3 back, and he indicated that he has installed thousands of units over the past decade and stands by his load calculations. He mentioned that he sized the units for AC, and by doing so, it will be more than enough for heat. Does that sound logical?

 

[woodgeek]

Not really.....your cooling loads are prob half of your heating loads.

 

[Seasoned Oak]

Not really.....your cooling loads are prob half of your heating loads.

Ill say,My cooling cost are about $40 if that for the whole summer while heating costs are many many times that amount when heating with anything but wood. About $1000 minimum.My homes Cooling Capacity is 22000 BTUS while heating is 95000 BTUs.

 

[Seasoned Oak]

All 3 companies did load calculations, which is why I was surprised by their very different conclusions. I called Company 3 back, and he indicated that he has installed thousands of units over the past decade and stands by his load calculations. He mentioned that he sized the units for AC, and by doing so, it will be more than enough for heat. Does that sound logical?

Ill be sizing my minisplit for heat, which will be more than enough for cooling.

 

[woodgeek]

What Randy said. ^^^

A NICE thing about minis is that their variable speed solves a problem. In a single speed (on/off) HP, sizing it for heating makes it oversize for cooling, leading to comfort and dehumidification problems. My singe speed system never runs more than 6 hours a day in AC, but can run flat out 24 hours in heating. But my dehumidification is just 'ok'. If it dried the air better, I could go a couple degrees warmer on the setpoint. Oh well.
A mini will throttle down for cooling and do a great, comfortable, quiet job of it.
Company 3 is starting sound like a loser.

 

[Seasoned Oak]

Hard to believe cooling load is greater than heating anywhere in the northern US.

 

[flyingcow]

is it the unit itself or the refer line vibrating? it is common for the line to vibrate.

outside unit. Not following the lines

 

[altmartion]

All 3 companies did load calculations, which is why I was surprised by their very different conclusions. I called Company 3 back, and he indicated that he has installed thousands of units over the past decade and stands by his load calculations. He mentioned that he sized the units for AC, and by doing so, it will be more than enough for heat. Does that sound logical?

somewhat.

 

[Dave A.]

When I was looking at heat pumps (not mini-splits) about two years ago. There were two types that seemed kind of appealing. One was what's called a reverse cycle chiller, which produces hot water to run to an air handler coil, or for in floor radiant (refrigerant stays in the outside unit, only the water, hot or cold, is circulated). Hot water temps were around 120F so not hot enough for baseboard heat. But what was nice about this is that you had stored heat in the water, so during a defrost cycle (where you normally lose heating capability with the heat pump) you would still have the heat from the stored hot water.

The other was a system with a dual stage compressor. And with one brand in particular you had a wide range of outputs for each compressor size. So like with a 36k BTU unit you could get as much as 72kBTU for heat out of it in the high stage or as low as 18k BTU for cooling in the low stage. This was nice because the problem with a lot of heat pumps in a mid-atlantic climate is if you size for heating you'll have too much cooling (and resulting poor dehumidification).

 

[DBoon]

You are getting a lot of good advice hear - nothing to add except that it is ok to go slow - just install one unit for now if you are worried about cost or want to see what the payback is like. One 18kBTU unit downstairs will throw a lot of heat (more than 18kBTU when temperatures are above freezing) and be the least cost option. You can always add more later if you want to.

Personally, I would get the Hyper Heat since I am an efficiency nut, but you'll still be plenty happy with the regular ones, especially if you are worried about the extra cost.

I personally wouldn't put much faith in what the installer says about Hyper Heats...the installers I talked to were remarkably unawares of the specifics of their products. I had to educate them and even specifically write down what I wanted them to quote me. It was a big eye opener. I would say that the quality of the advice you are getting here is likely better than what the installers are telling you.

 

[altmartion]

You are getting a lot of good advice hear - nothing to add except that it is ok to go slow - just install one unit for now if you are worried about cost or want to see what the payback is like. One 18kBTU unit downstairs will throw a lot of heat (more than 18kBTU when temperatures are above freezing) and be the least cost option. You can always add more later if you want to.

Personally, I would get the Hyper Heat since I am an efficiency nut, but you'll still be plenty happy with the regular ones, especially if you are worried about the extra cost.

I personally wouldn't put much faith in what the installer says about Hyper Heats...the installers I talked to were remarkably unawares of the specifics of their products. I had to educate them and even specifically write down what I wanted them to quote me. It was a big eye opener. I would say that the quality of the advice you are getting here is likely better than what the installers are telling you.

you also give good advise. sometimes, more than it should be, installers only know how to install. that is strictly what they do. some of the bigger company's around here won't let the install crew start the unit's. they are not trained like the techs or sales guy. if you want the real skinny on a product, talk to a good tech. they will most likely know more about it than the installer or salesman, and sometimes more than the manufacturer. lol. the tech can tell you reliability of a product and common issues.

 

[woodgeek]

You are getting a lot of good advice hear - nothing to add except that it is ok to go slow - just install one unit for now if you are worried about cost or want to see what the payback is like. One 18kBTU unit downstairs will throw a lot of heat (more than 18kBTU when temperatures are above freezing) and be the least cost option. You can always add more later if you want to.

Personally, I would get the Hyper Heat since I am an efficiency nut, but you'll still be plenty happy with the regular ones, especially if you are worried about the extra cost.

I personally wouldn't put much faith in what the installer says about Hyper Heats...the installers I talked to were remarkably unawares of the specifics of their products. I had to educate them and even specifically write down what I wanted them to quote me. It was a big eye opener. I would say that the quality of the advice you are getting here is likely better than what the installers are telling you.

Agree about going slow....but if he puts it downstairs, he has no AC upstairs in the summer.

 

[Floydian]

Hello Wear More Layers,

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.

I have to say, the specs on all the units you got quotes on are not all that impressive.

The MXZ-2B20NA is rated at 22,000 btus(heating) at 47 and only 12,500 btus at 17 and has an HSPF of 8.9 and a SEER of 18. Meh

The MXZ-4B36NA is rated at 35,400 btus(heating) at 47 and 22,000 btus at 17. I think the HSPF is 9.3 and the SEER is 17.5 but I'm not sure as my Mitsu catalog is a little vague with this unit.

As mentioned the Hyper heat units do quite a bit better but require the 1:1 configuration, also as mentioned. I was set on the Mitsu Hyper Heat for my folks super insulated house because of the superior performance vs the regular units. Then I started looking at the Fujitsu's and I encourage you to do the same.

Fujistu has the xxRLS2H series which is the direct competitor of the Mitsu Hyper Heat units but I think a better fit for you would be the xxRLS2 series, particularly the 12RLS2 or the 15RLS2 for your downstairs. http://www.fujitsugeneral.com/wallmountedRLS2_specs.htm

Heating specs on these units:

The 12RLS2 is rated at 16,000 btus at 47 and 15,000 btus at 5 and has an HSPF of 12.12,000 btus cooling and SEER of 25

The 15RLS2 is rated at 18,000 btus at 47 and 17,000 btus at 5 with an HSPF of 12 also. 15,000 btus cooling and SEER of 21.5

This units are also likely to cost less than the comparable Hyper Heat units.

Check for Fujitsu dealers/installers in your area and maybe get a couple quotes for two separate units. One upstairs and one down.

IMO, this would give you more bang for your buck and get you more heating capacity when you really need it without a lot of up charge over the quotes you have already received.

Sorry if this adds to your headache,
Noah

 

[Wear More Layers]

Based on everyone's comments and Noah's very recent post, I'm both worried and confused.

Worried because I invited Company 3 (two 12,000 Btus) back to talk me into a sale. I'm not made of money, and their $6K figure was the lowest by far yet still a huge pill to swallow. They also seemed to be the most experienced with installing mini splits. I will call them before they come over to press them on their statement that sizing the units for cooling will lead to more than enough capacity for heat.

Confused because I truly don't know what size units I really need. I'm definitely going to get a maximum of 2 units, but should it be 12/12, 18/9, 18/12, 18/18, 24/9……..? Only Company 2 showed me their heat load calculations and came up with ~39,000 Btus. Given 24,000 Btus from Company 3 and 36,000 from Company 1, I get an average of 33,000 Btus.

Nobody offered me Fujitsus as an option even though 2 of the companies are listed on the Fujitsu website as dealers (that's why I called them in the first place).

I guess in the end I really need to follow DBoon's advice and slow down. After several months of researching pellet stoves, wood stoves, and now mini splits, I had hoped to have settled into winter with some warmth. I guess I'll just have to Wear More Layers for a little while longer.

Don't let that stop you from continuing to offer advice!

 

[Wear More Layers]

One thing I just thought of: The companies that recommended 36,000 Btus and 42,000 Btus used as their baseline an indoor temperature of 75 degrees. I don't need nearly that much heat. I think Company 3 (24,000 Btus) took me at my word that I'd be happy with temps in the low 60s. Is it possible that 24,000 Btus in my house would lead to temps in 60s?

Interestingly, the company that showed me their calculations figured that the house needed 23,000 Btus for AC. That's right where Company 3 sized the units for, which jives with their statement that they sized the house for cooling and that this size would be enough for my heating needs.

Just a thought.

 

[Floydian]

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.
Then they have to assign the right R-values or the numbers could be all over the place. And they will have to guess about the air exchange rate unless you have had a blower door test done.
A real heating/cooling load calculation is going to take a least a couple of hours and they will want to charge you to actually do this I would think. Sounds like heating/cooling load guesses to me and they might be close or they might not.

In truth this is something you could do yourself along with some help here IF we have the right numbers to plug in or else...garbage in, garbage out.

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.

My main point was that if you are spending the coin on the mini's why not get enough capacity to use as little oil as possible. It could be doable and who knows, maybe you add some grid tie PV in the future to help offset your electrical usage. Yeah, we love to spend your money for you.

I know this stuff can be frustrating. Hang in there, a solution will present itself.

Noah

 

[woodgeek]

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.