MRCOOL DIY Mini Split, Seriously, I Think...

[Fueler]

My experience is this. Unlike conventional AC you can't oversize one of these inverters. They have smarts.

I am going to get roasted for that but that is my experience.

 

[bluedog225]

Another here to say thanks for this thread. Hope to be buying before the heat next summer. Lot of ground to cover before then.

 

[justinjoyal]

My experience is this. Unlike conventional AC you can't oversize one of these inverters. They have smarts.

I am going to get roasted for that but that is my experience.

Or do you mean the other way around ? (Not that it's a great idea to oversize your mini-split.)

Oversizing a conventional A/C is bad.

 

[jjrbus]

My experience is this. Unlike conventional AC you can't oversize one of these inverters. They have smarts.

I am going to get roasted for that but that is my experience.

Varys by manufacture a 12K mini will modulate from 3000 to 13,000 btu of cooling. I can babble on but have a poor memory, here is a link from someone who seems to know what he is talking about. Had I known this I would have used a smaller mini in one area of my house. An interesting read for anyone considering a mini!! https://www.contractormag.com/hydronics/hydronics-systems/article/20878662/sizing-mini-split-systems-dont-oversize-choose-the-right-equipment

 

[Raisedonadeere]

Minisplits do accommodate over sizing much better than conventional hvac but work best when sized to the load. The unit can throttle down to 30=40% of its max capacity but on mild days you are going to see a wide temperature swing as the unit sees the point often where it has to shut down the compressor.

Bigger is still not better except to cover any uncertainty in sizing estimates. In a close call, roll the dice and go up one size if you still insist. But I have personally seen in several installs that the mini splits somehow do more than expected and one size down would have been better at holding consistent temps. I am talking about well sealed and insulated spaces. Just about everyone I know is installing a unit one size bigger than they need.

 

[Phydeauxman]

Cool air sinks - you shoot for stratification.
I find it happening with my 15’ cielings - 75 at the floor and 80 at the ceiling. It’s very comfortable.

How high on the wall did you install your unit?

 

[Phydeauxman]

And of course, again you were correct!! I was able to maintain 78F yesterday without the fans on at all, letting the air stratify. I wasn't able to do that on Thursday with them on. I had 78F and 33% humidity, which was very nice to work in. I did play around and turned on the fans to see how much it would change things, and it jumped to 82 and 45% in about 3 minutes. Left them off after that.

I was considering installing fans until I read this...now I am re-considering. Would the fans help to push the heat down in the winter? My ceiling is 16'.

 

[justinjoyal]

I was considering installing fans until I read this...now I am re-considering. Would the fans help to push the heat down in the winter? My ceiling is 16'.

Yes you can use them in the winter to pull the warmer air down but not in A/C mode.

 

[mepstein]

I installed a 12K mini split in my 22x24 insulated garage. I permanently opened up the stairs to the 2nd floor so I'm installing a fan above the stairwell to circulate the air. Push down in the winter and pull up in the summer. My ceilings are only 8.5'.

 

[Browneye]

How high on the wall did you install your unit?

Right at about ten feet.
The top wallpaper trim is at about eight feet, or a normal ceiling height.

 

[yeldogt]

With AC in a high ceiling room -- you don't want to have fans running. The goal is to cool the people in the room -- not all the air in the room. Placing the bottom of the unit in the 9' range works well .. the unit can then blow across the room.

There is never a reason to over size -- why? .. you are never going to need it. In most climates you will need the lowest output and this is especially true in mild times of the year with humidity.

Always read the specifications ... understand the room load and the units output. Most mini splits have rated outputs greater than the stated ... except at the limits. Having a unit fall behind for a few hours a couple times every few years is better than oversizing. Kitchens being somewhat of an exception ... they often need a tad more.

 

[BrianS]

There is never a reason to over size -- why? .. you are never going to need it. In most climates you will need the lowest output and this is especially true in mild times of the year with humidity.

I followed your comments and you seem to be really knowledgeable about the multi-zone mini-splits. Any thoughts on my install?

I'm looking at doing a 2 zone Mr Cool DIY for my 24x32x14 garage with a 12x32 bonus room above. Insulated with R19 walls and R30 on the underside of the roof sheeting, so a large volume of space. Located in SW Ohio. I only plan to run in freeze protection mode in winter and cool to 80* or so in summer.

I'm torn between a 18k+9k (27k outdoor unit) or 24k+12k (36k outdoor unit). Price is only $300 difference, does it make sense to just go with the larger units?

 

[ericm]

HVAC load calculator: https://www.loadcalc.net/index.php

 

[Jim Caudill]

I had originally calculated around 18K for my 24x24 garage. My retired HVAC friend saaid "No way!" 9k is all you probably need. So we compromised and I bought an LG12K inverter unit. Here in Ohio it is not quite enough. I wish I had gotten the 18K unit and got the cold weather version that will operate down to -4 degrees F. When the temperature gets down to15 degrees, I use a hanging electric heater to keep the shop close to 60 degrees. IT costs between 2 times and 3 times as much to heat with the hanging heater.

 

[mobetta]

I'm looking at doing a 2 zone Mr Cool DIY for my 24x32x14 garage with a 12x32 bonus room above. Insulated with R19 walls and R30 on the underside of the roof sheeting, so a large volume of space. Located in SW Ohio. I only plan to run in freeze protection mode in winter and cool to 80* or so in summer.

I'm torn between a 18k+9k (27k outdoor unit) or 24k+12k (36k outdoor unit). Price is only $300 difference, does it make sense to just go with the larger units?

You probably want to ask on your own thread, but here's my opinion.
Id be tempted to go with the smaller one myself.... I think in your climate it'd do fine.


What temp do those units heat to?? many stop around 15F, some -5F and some down to -20ish.

I went to a 24K (mr cool hyper heat, -20f(??)) for my 24x26x11 but I stepped up a size for more winter btus. I have no experience with AC yet and it looks like our overall low temp this year will be only -6F so not the best winter to see how well it heats in extreme cold but it worked fine at that temp.

I do notice that it spends a lot more time in Defrost when its running FP mode.

at 62 set point it doesnt seem to cycle DEF as often???

 

[BrianS]

Looks like one vote to go big and one vote to go small. I think these units heat down to 5*.

I should add that I plan to install a 50k propane Mr. Heater as backup for the really cold days. The smaller units would probably be ok, just don't want to regret not spending the extra $300.

 

[Browneye]

I have never and will never agree with down-sizing. Being right-sized or a little over means it cools faster when it's needed.
IMO the heating benefit of the heat pump is just a bonus - it may be enough, but having some direct-heat source makes sense, gas-fired or electric. I prefer gas.

When it's a hundred out and you want to cool things off quickly, the bigger unit on turbo will accomplish that much faster. They all shut down when they get up/down to temp anyway.

 

[Stefan S]

Does the 18k unit require a fused or non-fusible disconnect?

 

[justinjoyal]

I have never and will never agree with down-sizing. Being right-sized or a little over means it cools faster when it's needed.
IMO the heating benefit of the heat pump is just a bonus - it may be enough, but having some direct-heat source makes sense, gas-fired or electric. I prefer gas.

When it's a hundred out and you want to cool things off quickly, the bigger unit on turbo will accomplish that much faster. They all shut down when they get up/down to temp anyway.

Humidity control.

 

[jjrbus]

Humidity control.

Bingo! Instant gratification vs long term comfort.

 

[Browneye]

Sorry guys - I want instant gratification.
And I want it to keep up when it's hot.
So far, out of my two, one is a little under, the other a little over (capacity) and I much prefer the over - it's ice cold, just what we want.

 

[justinjoyal]

Sorry guys - I want instant gratification.
And I want it to keep up when it's hot.
So far, out of my two, one is a little under, the other a little over (capacity) and I much prefer the over - it's ice cold, just what we want.

Sizing should be done according to your needs.

Oversized is what some people want and it's alright, as long as you understand the downsides !

 

[C2F]

Sizing should be done according to your needs.

Oversized is what some people want and it's alright, as long as you understand the downsides !

A quality ductless split system can be oversized. In some colder climates with no aux heat you can size the system based off the heating load. The system may be oversized for cooling however the inverter and electronic expansion valve will modulate according to the load. A 24K BTU unit may modulate all the way down to provide just 4,000 BTU of cooling under low load to prevent typical tempature swings normally seen with standard On/OFF air conditioning systems.

 

[justinjoyal]

A quality ductless split system can be oversized. In some colder climates with no aux heat you can size the system based off the heating load. The system may be oversized for cooling however the inverter and electronic expansion valve will modulate according to the load. A 24K BTU unit may modulate all the way down to provide just 4,000 BTU of cooling under low load to prevent typical tempature swings normally seen with standard On/OFF air conditioning systems.

And humidity will not be properly controlled.

It has nothing to do with « quality » btw. Inverters and EXVs allow for slight oversizing, but grossly oversize your system and comfort will suffer.

 

[ericm]

So what do you do when your heating requirements are 22k and cooling is only 10k? I assume you go with the higher value. Humidity is not an issue here during cooling season though it can be during heating season if there are wet cars being pulled in frequently.

 

[C2F]

And humidity will not be properly controlled.

It has nothing to do with « quality » btw. Inverters and EXVs allow for slight oversizing, but grossly oversize your system and comfort will suffer.

Your idea and my idea of over sizing must be very far apart. A 24,000 BTU conventional install can be replaced with a 36K ductless with zero humidity issues. For very humid times of the year the controller can be set to dry.

I’ve been to buildings after small remodels and Heads were cooling rooms less than half the size they were designed for, grossly oversized with zero humidity issues. And we have very humid summers. I’ve dealt with numerous lead engineers are employed directly by manufactures on system startups and we never ran into humidity issues except in the case when to much Outside air was ducted to the units.

 

[justinjoyal]

Your idea and my idea of over sizing must be very far apart. A 24,000 BTU conventional install can be replaced with a 36K ductless with zero humidity issues. For very humid times of the year the controller can be set to dry.

I’ve been to buildings after small remodels and Heads were cooling rooms less than half the size they were designed for, grossly oversized with zero humidity issues. And we have very humid summers. I’ve dealt with numerous lead engineers are employed directly by manufactures on system startups and we never ran into humidity issues except in the case when to much Outside air was ducted to the units.

Excessive humidity, excessive noise, larger electrical requirements, larger IDU/ODU, etc.. Not my cup of tea.

Of course it depends on the climate where the system is installed. If it’s usually pretty dry outside, humidity is less of an issue.

Around here it tends to be rather humid at times.

So what do you do when your heating requirements are 22k and cooling is only 10k? I assume you go with the higher value. Humidity is not an issue here during cooling season though it can be during heating season if there are wet cars being pulled in frequently.

You size according to your primary needs/goals and what you can live it.

If heat is what you want the most, size accordingly but understand the tradeoffs.

 

[C2F]

Excessive humidity, excessive noise, larger electrical requirements, larger IDU/ODU, etc.. Not my cup of tea.

Of course it depends on the climate where the system is installed. If it’s usually pretty dry outside, humidity is less of an issue.

Around here it tends to be rather humid at times.



You size according to your primary needs/goals and what you can live it.

If heat is what you want the most, size accordingly but understand the tradeoffs.

I stand by my statement if you live in a colder climate and have no aux heat then the heating requirement will be higher and the system will be slightly oversized for cooling.
The humidity on a proper system like a Mitsubishi PUZ series there will be ZERO humidity issues. I deal with ductless splits on a frequent basis.
.

 

[Stefan S]

Does the 18k require a fused or non-fusible disconnect?

 

[C2F]

Does the 18k require a fused or non-fusible disconnect?

I can not recall seeing a fused disconnect for a modern ductless split install.
Look at the install manual of the unit u want

 

[Browneye]

Excessive humidity, excessive noise, larger electrical requirements, larger IDU/ODU, etc.. Not my cup of tea.

Of course it depends on the climate where the system is installed. If it’s usually pretty dry outside, humidity is less of an issue.

Around here it tends to be rather humid at times.



You size according to your primary needs/goals and what you can live it.

If heat is what you want the most, size accordingly but understand the tradeoffs.

Give it a rest. People are contemplating a 2 ton vs a 3 ton, not doubling or tripling the size.

My 12k unit location would have been ideal for a 9K, but MrCool doesn't have one of those, so the 12K was installed. I got it for about $800. No humidity issues summer or winter - so-Cal is very temperate.

The other unit is a 2-ton, covers an area about 1200 sq ft with 15' ceilings - it could have easily been a 3 ton, but it works fine. When it gets over 100* with the sun on the west windows, it has trouble maintaining under 80. But it's good 95% of the time.

We get you want to save everyone from themselves.

 

[Browneye]

Does the 18k require a fused or non-fusible disconnect?

They have beat this to death here too. The code-junkies are just sure you have to have a fused disconnect if that's what the UL label says, but the pro's don't worry about it, just make sure there is a breaker up-line appropriately sized to your load and circuit.

The installation manual specifies wiring size and max breaker size. All breakers today are AC rated - all that funky coding was done away with years ago to simplify things. There is also a variance for breaker size vs wire gauge when applied to air conditioning. Whatever the manual spells our is fine.

If you have a really old panel or wiring system with fuses, then all bets are off.

And you do need a disconnect at the unit for servicing, to meet code. It can have a breaker there, or at the main panel, that is appropriate for your circuit.

 

[justinjoyal]

I stand by my statement if you live in a colder climate and have no aux heat then the heating requirement will be higher and the system will be slightly oversized for cooling.
The humidity on a proper system like a Mitsubishi PUZ series there will be ZERO humidity issues. I deal with ductless splits on a frequent basis.
.

If you live in a colder climate you should have aux heat. (And by colder I dont mean 40 degrees.. I mean places where below freezing temperatures are not unusual.)

Obviously if you dont have aux heat you will be forced to size for heating which will most likely mean oversized for cooling, can’t really work around that.

Give it a rest. People are contemplating a 2 ton vs a 3 ton, not doubling or tripling the size.

My 12k unit location would have been ideal for a 9K, but MrCool doesn't have one of those, so the 12K was installed. I got it for about $800. No humidity issues summer or winter - so-Cal is very temperate.

The other unit is a 2-ton, covers an area about 1200 sq ft with 15' ceilings - it could have easily been a 3 ton, but it works fine. When it gets over 100* with the sun on the west windows, it has trouble maintaining under 80. But it's good 95% of the time.

We get you want to save everyone from themselves.

Well, oversizing by 50% is not something I would advise, but as long as the customer is fine with it and understands the probable issues, then I'm fine with it as well..

I've had customers insist on a 18k unit when all they really needed was 9k... After doing some explaining, they still wanted to go ahead with it so thats what we did. They were happy, I got paid and that’s it.

Many times however they followed my advice and happily saved a few hundred bucks and they love their system. ;-)

 

[Stefan S]

Hi all just finished my install and it was super easy. Took me about 6 hours not counting the time to weld the brackets for the condenser.

I’m also going to list some extra pieces of line set in the classifieds. I needed part of a piece so I bought two sets. Thought maybe somebody could be in the same place and want to save some money.

 

[Browneye]

Terrific!

 

[vannjd]

I have had a Mr Cool in my 24 by 26 shop for about 2 years. it works great. I took 2 of us about 3 hours to install. My friend that helped was so impressed that he put 2 in his house and his heating and cooling bill is about half. He took out his furnace and window ac.

 

[Viz]

I have had a Mr Cool in my 24 by 26 shop for about 2 years. it works great. I took 2 of us about 3 hours to install. My friend that helped was so impressed that he put 2 in his house and his heating and cooling bill is about half. He took out his furnace and window ac.

My shop size exactly. What is your interior height, and what size unit do you have?

 

[Stefan S]

Mine is 25x25x9’3” and I run an 18k.

 

[clymer]

Hi all just finished my install and it was super easy. Took me about 6 hours not counting the time to weld the brackets for the condenser.

I’m also going to list some extra pieces of line set in the classifieds. I needed part of a piece so I bought two sets. Thought maybe somebody could be in the same place and want to save some money.

..nice work. Nice dog

I am in NH, used a 36K condensor multi-head unit with three heads (two 9 k's and a 12 = 30k total), yes the condensor was oversized for the head units, but it's all ingrams had at the time and I can heat this place to 80 degrees when it's in the teens outside, and cooling the place is no problem. My backup heat is forces hot water / hydronic via wall-mount propane combi unit and I have a wood stove for power outages, because I am up in the windy mountain tops here)

 

[Heiny57]

I just bought a Mr cool and had a question on what size line set hole is really needed. I know they say to drill a 3 1/2 to fit the provides sleeve through the wall. I briefly examined the line set and don’t see the need for such a large hole. Has anyone drilled a smaller hole to run the lines? The reason I would do a smaller hole is it would be easier to patch when I move and take the unit with me.