40x60x16 Mini Split? Heat Pump? Propane?

[kgasaway]

Hello,
I need to get some equipment ordered to heat my new shop.
I am located in central Oklahoma. We get some teens and 20 degree weather in the winters.
The 3 14x14 doors are well insulated and the rest of the shop will be 1-1.5” closed cell spray foam.
There is no gas in my neighborhood, so I’m stuck with electric or propane. My house has a 5 ton heat pump that works well, I am considering the same for my shop but have seen all the posts regarding mini splits and wondering if that might be a good option for me as well.
Does anyone have any experience with mini splits in a space this size?

 

[ducksface]

This is heresy but I'm saying it anyway.

Minisplits are ONLY for individual areas where hvac can't reach
Or
There is a space constriction causing you to have to use a minisplit.
Or
A cost constraint

Everything else is better served by a system as is on your house.


There is no value to me of a single air outlet trying to work in a garage the size of yours.
Standard Minisplit is a veritable permanently placed box fan with heating and cooling.

Put in ducts, enjoy the home type system you enjoy in your home.

 

[kgasaway]

Thank you for your reply Ducksface, I am leaning that way as well.

I am thinking of using a traditional heat pump and possibly using an air sock running the length of the shop.

 

[yeldogt]

Have you done a load requirement ?

As you know a heat pump has a rated output at a given temp -- you must match what that is to how you want to heat the building.

My outbuilding/ studio is 1700 sf and is very well insulated -- more foam thickness than you and only one door. Very tight. Being able to heat a large space with a single point is all about air leaking .. AC is a bit different as it's more about lowering humidity. I have no problem with heating mine with a direct vent sealed combustion cabinet type heater ...mine is net of 32k BTU ... but, when my propane was disconnected I was able to keep it warm with 14k BTU of electric. My space has a mini as well. With my electric rates the propane is a bit cheaper to operate -- so I tend to use the propane to keep the temp close to what I want and use both when I want to quickly bring it up a bit. I only use it on the weekends mostly. The single point 24k BTU mini has no problem with the AC.

With any amount of closed foam the leaking is taken care of -- its all about the doors. If they leak you will need to have heat/cool source near them to counteract the loss.

So -- it really comes down to cost ... some with cheap electric power go HP. The problem you may have is the split HP's with good cold output tend to be expensive and the stand alone mini-splits often are 1/3 more efficient vs them anyway. Matching heat often oversizes the AC side.

You need to get that heat load done and plug in how you want to use the space

 

[ducksface]

https://senior.com/products/sunheat...R6d5rIYJshSB0c-GzciStciefBaDLbRxoC59kQAvD_BwE

I use three of these.
I don't have a humidity problem so it's not a thing here.
They've never set off the gas sensors.

At the 9 to 12 cents pkw we pay for electric, propane is a breakeven at $3 a gallon.
(or thereabouts. Close enough for us.)

 

[kgasaway]

Yeldogt, Thank you for the reply.

I have not done a load requirement, I have tried to do a few online but haven't been successful.

To answer the door question, they have seals on each pane as well as the sides and top seals. I feel that they seal well.

 

[ericm]

Don't forget that the heat pump is much more efficient than the 100% you get from resistance heating. 3.0 at 30 degrees is not unusual. It can be a lot more (see below for COP discussion)

For me propane is about $2.75/gal or .10 per kw. (91500 btu/gal and about 3400 btus per kw)
Electricity is .27/kw. We go into tier 2. We have to run a well pump so we use more electric than people in town.
But at 3x the output from a mini split @ 30 degees the cost drops to .09 per kw of heat/cooling making the costs roughly equal for propane heat vs mini split.

And the mini will both heat and cool, which you're gonna need in Sacto and I will need in my shop here.

Coefficient of Performance is the amount of heat (or cooling) output vs the electricity to run the unit. Since a mini split is just pumping heat from one side to the other, it's much more efficient than making heat through resistance heating.
Heating COP decreases as the external temp decreases. 3 at 30 degrees is good but not uncommon. But when it's 50 degrees it may be 4 or 5. Likewise for cooling- 3 at 110 degrees but at 80 it could range from 4-8. So my calculations above are kind of worst case (at least for my climate). When it's not so cold/hot and the unit is not working as hard, it is more efficient. That's most of the time here.

With that, even with my expensive electricity, the operating costs of mini splits would win out over propane heating. However it will take longer for mini splits to quickly heat a shop that's been cooled by leaving big garage doors open than for a propane heater that puts out a lot more BTUs.

 

[yeldogt]

I just filled my new 1000g propane tank at 1.59 gallon ..had it been installed earlier I would have been able to do it cheaper My electric is just above .20 KW . So the propane at 80% is close to 1/3 the cost of resistive. Not quite. So using the HP --- I have to be pushing 3.0. They can get that around 45 degrees .... when it's cold the HP can still heat the place ... but the propane ends up being less costly.

split system is not going to hit 3 .... With NG it's always use NG.

The load is what matters --

 

[SALIV8]

If I had the choice of propane and electric, or just electric, I’d go the mini split route assuming this shop is a wide open floor plan.

1 on each end. I’d be looking in the 18-24k range depending on specs of the units. Check for your local rebates as well.

 

[meathooker]

A ducted system like your house with a HP and propane backup would be the ultimate setup.

To make a space feel comfortable you need to move some air. Mini splits just don’t do that well.

Also look at doing 2” closed cell. Most manufactures show and air permeance of zero at 2”.

 

[kgasaway]

That sounds like a pretty good idea Meathooker, thank you for your input.

 

[HoosierBuddy]

OK....Just to make a point in case no else already did:

Heat pump solutions (standard or mini-split) don't work well for "part time" heating.

Your typical heat pump overcomes this deficiency by including a resistance "emergency" element, that will kick in to bring a space up to temp in a reasonable amount of time, but this returns the systems COP to 1.0, likely using 4 times as much electricity per BTU while it runs....and it's producing a heck of a lot more BTUs per hour than it would in "non-emergency mode". This is often referred to as a "meter spinner".

My point being...in the OP's situation either a right-sized heat pump or mini split solution would work if the heat is going to be on full time without a lot of thermostat adjustments. If this is a part time heating solution, propane would be much cheaper.

Comparing heating full time with a heat pump vs part time with propane....the propane solution (part time) would be much much cheaper. Likely a fraction.

Good luck!

Phil

 

[yeldogt]

That sounds like a pretty good idea Meathooker, thank you for your input.

It's also the most expensive solution ..

 

[yeldogt]

OK....Just to make a point in case no else already did:

Heat pump solutions (standard or mini-split) don't work well for "part time" heating.

Your typical heat pump overcomes this deficiency by including a resistance "emergency" element, that will kick in to bring a space up to temp in a reasonable amount of time, but this returns the systems COP to 1.0, likely using 4 times as much electricity per BTU while it runs....and it's producing a heck of a lot more BTUs per hour than it would in "non-emergency mode". This is often referred to as a "meter spinner".

My point being...in the OP's situation either a right-sized heat pump or mini split solution would work if the heat is going to be on full time without a lot of thermostat adjustments. If this is a part time heating solution, propane would be much cheaper.

Comparing heating full time with a heat pump vs part time with propane....the propane solution (part time) would be much much cheaper. Likely a fraction.

Good luck!

Phil

The OP has one in his house .. so, one would hope he understand what's going on with the equipment.

Years ago the resistance strips were a necessity just to make sure you could have heat when it was cold out. Builders would use heat pumps in areas where they really should not have. They were cheaper to install vs doing a furnace .. the builder did not care about running costs after the sale. The homeowner had a month running the resistance heat strips and get a big bill. Today you can have a heap pump in very cold weather -- it's all about getting the proper size.

You are correct -- big setbacks don't work with heat pumps.

 

[meathooker]

It's also the most expensive solution ..

I said it was the “ultimate” ... that usually doesn’t mean cheapest.

 

[Rabbit929]

I have 3 mini splits in my home and boiler heat.
Boiler heat is awesome, if I was pouring a slap I’d pay the extra $ to have heated floors, expensive to install but cheap to operate.
Plus your floor never stays wet, and you could sleep on the floor if you saw fit.
As for mini splits, I agree with everyone else. These work good in small places But for a shop I’d just get a central system and mount it up high where the heat is. Mini splits are efficient but they lose some capacity from the FreeOn plumbing to and from your heat exchangers.
And they are a pita to clean, because of their low Fan speed they get dirty fast, and will start molding fast. I had to clean mine dramatically every 3 months till I learned to keep the fan off as the wet heat exchanger attracts dust, then it molds.

Central cooling and a heat pump would be the best bet hands down for long term low cost operation and durability.

 

[dwegner]

I'M in the Tulsa area and have a 30x60x13 with 3 overhead doors.
I have spray foam walls and a foot of fiberglass on the ceiling.
I put in a 3 ton mini split heat pump when I built it 5 years ago and it is probably the best thing I have made about this building. I keep it 60 in the winter and 82 in the summer and drop it to 74 in the summer and 69 in the winter when I am working out there.
It has cost me approx. 40/ month to heat and 60/month to cool it.

 

[Jackfre]

Should you go the mini-split direction with temps described you do not need the -20*f rated equipment. The standard heat pump models are generally rated to operate down to 5*f which is all you should need. Make sure you understand the specs on any unit you are thinking of.

 

[ericm]

@dwegner how long does it take to raise the temp from 60 to 69?

 

[kgasaway]

Thank you for the reply dwegner. Do you have any auxiliary (electric/gas/propane) heat or just the heat pump?