Mini split installation for a house

[Zachary Hoyt]

Got a call this morning from the guy who was going to put in the mini split, saying his supplier had a preliminary materials list that came to $4800. I said that was more than I would be able to afford. If I remember correctly a couple of months ago he had mentioned $2k+ as the likely materials cost, so I was a bit surprised. I imagine this is a "don't want to do the job" quote. I have been looking at the 4th generation Mr Cool units like Jim Becker is buying for his shop, and they say they are able to heat down to -13(not that I want to anyway) and can be installed by a normal person with normal tools, so that all sounds pretty hopeful. I am thinking an 18k BTU unit might be right, given the smaller size of the house, and it looks like I could get a kit with everything for a bit over $2k or so from various suppliers. I'll just have to hope there are good instructions.

[Bill George]

Zach the Mitsubishi I put in had one of the highest SEER 24 AHRI Ratings on the market, if not the Highest. They are AHRI Certified not just advertising claims. It still uses Flare fittings I believe even now, but the unit has the complete charge contained. I ordered with the shortest line set, 15 ft long. Both lines insulated as they should be for a heat pump. Your guy is BSing you, most of those mini splits today come as a package you just need to get the correct line set.

My son got me a wholesale his company price and I am still CFC Certified to work with refrigerants so I had No issues getting the $300 Rebate after they inspected the install and got the AHRI number off the nameplate.

I looked at one of those Mr. Cool install videos and they do a good job of showing you what to do and even leak checking... and they are using insulation on Both the lines as they should for a heat pump.

[Zachary Hoyt]

I don't understand SEER enough to know how much difference there is between the unit I am looking at which is 22 SEER vs 24 that you mentioned. I watched a video too and it looks well within my ability, I think. Flaring is something I would just as soon not have to do, though it would doubtless come in handy again someday if I learned it now.

[Jim Becker]

Zackary, the Mr Cool 24K BTU unit I bought via Costco was $2299 plus tax with free shipping. I was expecting a couple of weeks, but delivery is scheduled for next Tuesday. The single head 18K BTU unit is $1899 plus tax and the two head 18L BTU unit is $2799 plus tax. No vacuum pump is required...just electrical and a few other odds and ends are needed to complete the install.

[Lawrence Duckworth]

I don't understand enough to know how much difference there is between the unit I am looking at which is 22 SEER vs 24

zach.....the difference between 22 and 24 is 2

[Jim Becker]

I don't understand SEER enough to know how much difference there is between the unit I am looking at which is 22 SEER vs 24 that you mentioned.

24 SEER is slightly more efficient for cooling than 22 SEER, but these units are "way up there" in efficiency compared to most traditional HVAC systems. For where you live, the "cold temp limit" is probably more important if you are comparing two or more options, honestly.

[Zachary Hoyt]

I do have a general understanding of the concept of 2, most days, but I don't know if the scale works like decibels do, or is a more conventional system. I can't even remember the right words to describe these systems.

I don't plan to use the mini split in sustained sub-freezing weather, as the wood stove is well able to heat the house. I haven't been able to find any information about how cold of a temperature they can withstand while just sitting there idle, but I imagine if one can keep making heat down to -5 it would probably be able to survive without damage even down to -30 or -40 on rare occasions.

Thank you Jim for posting the prices. I'm not a Costco member, but I'll have to look into what it would cost to join, and if that would be cheaper than buying one elsewhere. I'd also need to get the wall mount bracket for the outside unit.

I am still a bit confused about what size to buy. The main part of the ground floor is a bit under 500 square feet, but with 9 foot ceilings and several large windows. It is also very well insulated as the whole house is now spray foamed. I don't plan to use the mini split in really cold weather, and our cooling load is not that high up here, where the nights are usually cool even in the middle of the summer due (I think) to the higher elevation. We rarely get many days over 90 in the summer. Some things I have been reading talk about the greater risk of undersizing the system, and some of oversizing. Based on the manufacturers recommendation we'd be somewhere between a 12k and an 18k unit depending how much of the house is considered. Counting the upstairs and the added bedroom we're still under 900 square feet, not counting attics, which are spray foamed but will be kept shut off most of the time.

Thank you all for your help, I really appreciate it. I'm hoping to get something ordered in the next week or so, and get it put in as soon as it arrives, weather permitting. Tomorrow morning is the final electrical inspection on the house and workshop, so I am a little nervous.

[Tom M King]

You don't have to do any flaring if you can make the stock length of the lineset work. If it runs under the house, you can just let it snake around some extra. If you're limited with how the lines have to run, an end may need to be flared.

You can get a Parker fitting that works much like a Sharkbite to adapt a cut line with a flare end. I haven't used the flare adapters, but have used couplings and elbows and am pretty impressed with them. I used them on a bad line in a rental house, but they may be as expensive as buying a good flare tool, but there are other options. I just didn't want to braze where I needed to use those fittings.

They are Really efficient. We cooled 7,000 sq. ft. with 18k btu this Summer for all but two days. Our house is super insulated. I had that unit put in for my Mother's Suite when she had to move in with us because I thought she would want her part warmer than we do, but she didn't. I did a bit of rearranging of ducts under the house so we can run fans only in other systems so it moves it around in a circle. So far, with a few nights down close to freezing, it's working well for heat too. I think it will serve us through the Winter because we have a gas heater we can add when it gets cold for long. It saved us over 200 a month this past Summer with no loss of comfort, and less noise.

With that in mind, 18 sounds like too much for 500 sq. ft. I think you could make ice in there in your Summertime, but they do adjust on their own really nicely, so you may make good use of the heat.

Check Supplyhouse for price too. They sell Mr. Cool, and have really knowledgeable people working there. Their stuff gets here the second day after I order it. I have a pro account there, which gives some discount and free shipping on any order regardless of size, but you have to be a building pro and have a website, and be approved.

[Bill Dufour]

The term you are seeking is logarithmic scale. I do not know if seer is that way or not. I know db sound is a log scale.
Bill <D

[Walter Mooney]

Zach, I bought a DIY Mr Cool unit from Costco after reading Mr. Becker’s recommendation. It was delivered in two boxes. The directions were great — clear, concise, and very easy to follow. I poured my own slab for the outdoor unit because I couldn’t get one anywhere close to my little shop in the TX Hill Country. Then the next day, installed the unit, with help from my son, and had it up and running before 2 PM! The biggest thing to be careful of is the connection of the two lines in the two different places. Be extra careful starting the threads, pay attention as you tighten them, and everything else is a piece of cake. I couldn’t be happier with my unit and the ease of installation. I’ve only used it for cooling thus far, but none the less, I am a very satisfied customer.

I thank Mr. Becker for his many ‘on-point’ posts. Good luck to you!

[Michael Schuch]

Oversizing a mini split kills its efficiency.

18,000 btu sounds too big for 500 sqft to me also. It will work and cool but it will run at a lower efficiency rating than advertised. Getting the right size unit is the key to efficiency. None if the HVAC guys I ever talked to ever calculated load (probably didn't know how to). They all pretty much shot from the hip... What do they care, they aren't going to pay your electric bill.

[Bill George]

I agree and a lot of HVAC guys are self taught and do not have a clue about load sizing. I learned the Manual J software heating and cooling load calculation and then taught the subject. However the Mini split I have adjusts to the load and the SEER rating more or less holds true. My heating and cooling costs for that area are very reasonable and with sizing don't forget the sun or solar load on the exposed glass.

The Mr. Cool seems to be a decent system IF you can follow directions and IF there are no issues.

[Dwayne Watt]

I do have a general understanding of the concept of 2, most days, but I don't know if the scale works like decibels do, or is a more conventional system. I can't even remember the right words to describe these systems.

I don't plan to use the mini split in sustained sub-freezing weather, as the wood stove is well able to heat the house. I haven't been able to find any information about how cold of a temperature they can withstand while just sitting there idle, but I imagine if one can keep making heat down to -5 it would probably be able to survive without damage even down to -30 or -40 on rare occasions.

Thank you Jim for posting the prices. I'm not a Costco member, but I'll have to look into what it would cost to join, and if that would be cheaper than buying one elsewhere. I'd also need to get the wall mount bracket for the outside unit.

I am still a bit confused about what size to buy. The main part of the ground floor is a bit under 500 square feet, but with 9 foot ceilings and several large windows. It is also very well insulated as the whole house is now spray foamed. I don't plan to use the mini split in really cold weather, and our cooling load is not that high up here, where the nights are usually cool even in the middle of the summer due (I think) to the higher elevation. We rarely get many days over 90 in the summer. Some things I have been reading talk about the greater risk of undersizing the system, and some of oversizing. Based on the manufacturers recommendation we'd be somewhere between a 12k and an 18k unit depending how much of the house is considered. Counting the upstairs and the added bedroom we're still under 900 square feet, not counting attics, which are spray foamed but will be kept shut off most of the time.

Thank you all for your help, I really appreciate it. I'm hoping to get something ordered in the next week or so, and get it put in as soon as it arrives, weather permitting. Tomorrow morning is the final electrical inspection on the house and workshop, so I am a little nervous.

this calculator might help you understand your sizing needs: https://www.ecomfort.com/stories/143...d-You-Buy.html
The shortcoming of this estimator is not having a specification for wall or ceiling R-values.

[Jack Frederick]

It used to be that the rule of thumb for cooling was 400 sq ft/ton. One ton=12000 btu. In Orwell NY for a primarily cooling unit an 18 is almost double what you should get. Mind you, you get some buffer on sizing as the units modulate. My 12 k unit modulates from 3200-about 14000. Over sizing a cooling unit hurts the dehumidification operation which is what you need most in the NE. Folks will tend to go larger when sizing for heating. One thing to consider in picking the unit is that a Hyper-Heat model which can heat to those lower temps is invaluable when you are away and the stove is out. It can prevent freeze-ups…some. SEER is seasonal energy efficiency rating and is used for cooling efficiency. HSPF is Heating Seasonal Efficiency Rating. The thing is on the ratings they basically test them as a standard single stage unit negating all the benefits of the modulation. They do the same on AFUE on Gas heating. When the 410a inverter minis came out standard AC was 10 seer and the US manuf fought like hell to not have to meet the 13 seer gov’t requirement. In ‘06 I installed a Fujitsu in my home that was 24 seer and heated down to -5*. it was magic. In speaking with one of the Japanese engineers from Fujitsu he said that if they could actually test the units properly they would be coming in in the mid 30’s seer wise.
In your place Zack I would do a 12k unit for that primary space. You can use products like Tjernlund Products, Airshares to move air to other rooms or you can cut registers into walls high and low to encourage air flow. That works.

[Jim Becker]

Zachary, Costco "regular" membership is like $60 annually and "Executive" membership is $120.

The 18K BTU unit may very well do the job for you. If you have direct floor vents between the first and second floors, even better. But jack is correct that the 12k BTU unit would likely do well for just the primary space. The cost difference is only a few hundred and unlike traditional HVAC systems, mini splits tend to compensate better for "more than you need" because of their completely variable heating/cooling/airflow model.