Mini split sizing and selection for 26x30 barn with 10' ceilings?

[TimberMan]

I am getting ready to run the electrical for my 26x30 gambrel barn and need to start thinking about which mini split, and which size I will use to heat and cool the first floor. I have 10' 6" ceilings (10', 2x6 studs on 24" centers on top of a 6" concrete curb which is part of the monolithic slab) plus the stairwell above the second floor. Walls will get R19, ceiling will get R38 and I am in central NC in climate zone 4a (although right on the edge of 3a).

I am looking for recommendations on which size unit to get as well as which make / model so that I can do the install myself and have my HVAC guy just do the final connections and charging.

Thanks!

 

[jblnut]

I don’t have professional advice but …..

I have a 6k btu window shaker in my 54x72x18 that’s cooling around 3,500ft/sq by itself and it does okay. It takes the humidity out but that’s about it. I have another identical unit in the office area that’s 14x16 and you can leave milk out on the table in there if you crank it to its coldest.

That being said ….. I just ordered a Fujitsu 24,000btu mini split for the big part and a 7k for the rest will do the office and upstairs hangout room. Should be plenty to dehumidify the shop part and coldify it decently. I’ll let you know in a few weeks !!

 

[pcmeiners]

There are many posts in this sub forum discussing your the sizing of mini splits for your garage size, 12k is what I have and is plenty for my 30x36 garage in PA with onnly average insulation, search the forum.

 

[The Metric System]

The various equipment suppliers have sizing tools that are generally pretty good, although they are intended for residential spaces so you have to apply a bit of additional re-rating to the results based on what you know of how the space will be built and used.

For example, garages (and presumably barns) typically have big poorly-sealed doors but also different expectations for HVAC performance and temperature control.

The calculator from Pioneer is good: https://www.pioneerminisplit.com/pages/hvac-calculator

Using the size/location information you provided it's saying you'd need a ~24,000 BTU unit which sounds about right to me.

The turndown ratios on minisplits are so good that IMO it's worth rounding up if you can afford the purchase cost and meet the space/power requirements. A unit that is too big will just run a lower capacity to meet the actual demand, but one that is too small won't keep up with the load.

If you aren't going to spring for a top-quality unit from Mitsubishi or similar I suggest you're best off buying the cheapest commodity product you can find in the highest SEER rating you can afford, as the lower-end units are all pretty interchangeable regardless of the brand they put on the sticker.

When I recently purchased a minisplit I found the best deal at Costway; sign up for their email list and they'll send some worthwhile coupons that will reduce the price further.

This is the unit I bought in a similar situation for a slightly larger building: https://www.costway.com/24000-btu-wifi-enabled-mini-split-air-conditioner-and-heater-black.html

 

[TimberMan]

Thx folks.

 

[pcmeiners]

For any minisplit buyers in areas requiring considerable heat, which is most of the country, SEER is not as important as a high HSPF number, average heating costs far more than average cooling costs. Only in the deep south and the south west does SEER become the important number.

RHC for Single-Family Homes | US EPA

This page describes the potential for renewable heating and cooling applications in single-family housing.

19january2021snapshot.epa.gov

 

[racecougar]

As with any similar purchase (many variables), a spreadsheet helps here. This is one I threw together years ago when deciding on which mini-split to buy for my shop.

 

[Notgrownup]

My 24x24 is fitted with a 18000 btu, i believe a 24k btu would serve you better with some strategically placed ceiling fans it would heat/cool your place good. I’m just east of you. I keep mine set at 81 in the summer and 64 intone winter all to keep moisture away from my lumber And comfort for tinkering around.

 

[TimberMan]

My 24x24 is fitted with a 18000 btu, i believe a 24k btu would serve you better with some strategically placed ceiling fans it would heat/cool your place good. I’m just east of you. I keep mine set at 81 in the summer and 64 intone winter all to keep moisture away from my lumber And comfort for tinkering around.

Thx. I am not sure about over or under sizing the inverter units but I want to be sure I can dehumidify in the summer without having to turn the temp down into the low or mid 70s….that will be below the dew point and I’ll have a disaster when I open the overhead door.

How tall is your ceiling and what r-value insulation do you have?

 

[PoorUB]

I used to cool my 24x38 shop with a 12,000 BTU window unit. It would keep up just fine, but it wouldn't catch up if I waited to turn on the unit later in the day. So my shop is a bit larger than yours, plus not as well insulated. 12,000 should cool it just fine, but you may want a larger unit for the heating capacity. In your area I would not go any larger than a 18,000.

Also, many people miss out on the fact that as it gets colder outside the heating performance drops off. When you narrow down the brand, take a look at the output at various outdoor temperatures and be certain the unit will heat in the coldest temps you experience. Some stop heating at 10F, some keep rocking until -20F.

 

[dcg9381]

Thx folks.

It's be helpful to know:

• What your geography is (PA is way different than TX)?
• Do you need to heat also?
• R-value and type of insulation (if any)?
• Any big-*** leaky additions - like large roll-up doors.

It's not as critical to size these things as it is traditional HVAC, as they can run partial power and often have dehumidify mode.

The other thing to know is if you're heating and cooling full time. If so, you can do a manual-J and get close. If not, you "oversize" (in my opinion) so you can rapidly heat/cool.

Heating performance (or lack of it) can be a killer, so definitely watch that. My 2 x 24K units will cool 2400 sqft, but will not heat it in the colder days of winter... My units are 17 SEER pretty basic, no hyper-heat.

 

[mike93lx]

I wouldn't put in smaller than a 24k and I would also add a standalone dehumidifier. Let the dehudifier stay at a set point of about 45-50% then have the a/c do cooling, heating and any additional dehumidification necessary

 

[Notgrownup]

Thx. I am not sure about over or under sizing the inverter units but I want to be sure I can dehumidify in the summer without having to turn the temp down into the low or mid 70s….that will be below the dew point and I’ll have a disaster when I open the overhead door.

How tall is your ceiling and what r-value insulation do you have?

10‘ ceilings, blown insulation, R-19 pink insulated in the walls and the styrofoam garage door kit from Home depot. It stays dry in there and I never use it on dehumidification mode. Like yesterday it was hot, 81 degrees was really nice in there.

 

[TimberMan]

10‘ ceilings, blown insulation, R-19 pink insulated in the walls and the styrofoam garage door kit from Home depot. It stays dry in there and I never use it on dehumidification mode. Like yesterday it was hot, 81 degrees was really nice in there.

Wow, very similar. Do you also have a 2nd floor? I have the the door to the attic at the top of the status so that stair well is also conditioned volume. Thx

 

[Notgrownup]

No only a set of folding attic stairs and light storage, it’s only a 3/12 roof pitch.

 

[TimberMan]

It's be helpful to know:

• What your geography is (PA is way different than TX)?
• Do you need to heat also?
• R-value and type of insulation (if any)?
• Any big-*** leaky additions - like large roll-up doors.

It's not as critical to size these things as it is traditional HVAC, as they can run partial power and often have dehumidify mode.

The other thing to know is if you're heating and cooling full time. If so, you can do a manual-J and get close. If not, you "oversize" (in my opinion) so you can rapidly heat/cool.

Heating performance (or lack of it) can be a killer, so definitely watch that. My 2 x 24K units will cool 2400 sqft, but will not heat it in the colder days of winter... My units are 17 SEER pretty basic, no hyper-heat.

I had most of that info in my original post except for the OH door which is 16x9 and will be insulated with r5 or 6 foam board and i didn’t mention that I will use the mini for heat as well.

Here are the other details:
I have 10' 6" ceilings (10', 2x6 studs on 24" centers on top of a 6" concrete curb which is part of the monolithic slab) plus the stairwell above the second floor. Walls will get R19, ceiling will get R38 and I am in central NC in climate zone 4a (although right on the edge of 3a).