Garage mini-split + propane heater results

[BrianS]

I did a lot of research here before installing the HVAC system in my garage, so I thought I'd share the results, especially after this recent cold snap.

Building is 24'x32' with 14' ceilings and attic trusses with a bonus room. Walls are insulated R-19, roof has 3" spray foam covered with R-13 batts for about R-21. Location is SW Ohio.

I installed a 36k DIY Mr. Cool unit with a 12k head upstairs and a 24k head in the main area. I also installed a 50K BTU Mr. Heater hanging propane heater as back-up if the mini-split couldn’t keep up.

Everything has been working great for the last year or so. During the summer I set the mini-split at 78* and it has no issue staying right on target. During the winter, I use Comfy Mode on the Mr Cool, since it has a minimum temperature setting of 62* and I didn’t want to keep it that warm. With Comfy Mode, I have it set to turn on the heat at 50* and turn off at 55*. This keeps it right around 52* most of the time. I have the thermostat on the propane heater set at 45* so if the Mr Cool can’t keep up, the propane heater will keep it above freezing.

This recent cold snap was a real test for the system and it did great. We had lows around -6* and the Friday before Christmas I don’t think it got above 0* that day. The picture is from my remote thermometer in the building. You can see the smaller temp swings from the mini-split. Then during the coldest time, the larger swings are the propane heater. Then as it is warming up outside, you can see them alternate. It really is working even better than I hoped.

 

[LostCauseRanch]

Thanks for sharing, I am contemplating a similar mixed setup with the mini split and a propane tube heater. I have a heat pump on the house so the I agree with you that the backup propane heater is necessary when we get as cold as it has been.

Does that thermostat app give you the total run time?

Did you have the high winds like we did coupled with the cold? That stretch last week here was the hardest my heaters have worked in the 6 years I've been at this house.

 

[BrianS]

The Mr. Cool app does show total run time. It used to show a timeline of when and for how long it ran, but doesn't seem to do that anymore.

On Friday, the coldest day, it ran for a little over 9 hours. Subsequent days it runs for 3-4 hours per day.

We did have the super high winds to go along with the low temps. It definitely was a good test of the system!

 

[solo machinist]

Thanks for that information. I'm in Lima, and looking at heat pumps with propane back up for the house and shop.
I can't remember it being this cold for so long. I'm looking forward to the warming trend coming.
Would you say the cost is minimal for running the system?

 

[Bolson32]

Thanks for sharing, I am contemplating a similar mixed setup with the mini split and a propane tube heater. I have a heat pump on the house so the I agree with you that the backup propane heater is necessary when we get as cold as it has been.

Does that thermostat app give you the total run time?

Did you have the high winds like we did coupled with the cold? That stretch last week here was the hardest my heaters have worked in the 6 years I've been at this house.

Can I ask what setup you have in your house?

 

[BrianS]

Thanks for that information. I'm in Lima, and looking at heat pumps with propane back up for the house and shop.
I can't remember it being this cold for so long. I'm looking forward to the warming trend coming.
Would you say the cost is minimal for running the system?

I can't say I've noticed any difference in our power bill month to month. The system is very efficient from what I can tell.

 

[dcg9381]

Thanks for posting that. Looks like it hangs in there even at -6, which is something that surprises me. It does appear to be running frequently (as expected) in that environment. You've got more than enough heat with the propane backup and are probably good for a "power out" situation too!

 

[thammel]

Just about exactly my situation. I have a 28x32 with attic trusses for a room up top. I have an 18k btu mini split downstairs and a 9kbtu one up stairs. The 60k btu propane Reznor UDAS in the first floor helps a ton when things are really cold. What amazes me is the very warm air blowing out of the mini splits (Mitsubishi Mr Slim) even when it is 10F outside.