Mini split or forced air?

[TwinFins]

I was set on a low cost traditional forced air furnace/AC unit....The more I read threads on this site the more I am considering a mini split system. I would do the majority of the install for either with an HVAC pro doing the final connections and an inspection.

The space is a fully insulated three car garage in Michigan with about 300 sqft of insulated finished workshop space above. Heat and air would only occasionally be used nights and weekends when I am out there.

Hardware costs seem to be cheaper for the forced air unit and install looks a little easier on the mini split. Duct work for the forced air system would be exposed round duct for an industrial look...

Which way should I go?

 

[bzinsky]

I'm a big advocate of mini-splits, but largely in part due to their efficiency. You need on demand hvac, your goal is to rapidly heat or cool a space. The mini-split likely just not have the output you'll need. It's great to maintain, but not to take a frozen garage up to room temp in 20 minutes.

I have a forced air system in my garage and I love it, 2 car detached garage, 80k btu's. It's perfectly oversized as I can work comfortably in about 20 minutes in the dead of winter.

The mini split would do well for AC though, as it takes the humidity out quickly and taking a garage from 95 degrees to 75 degrees is a lot easier than taking it from 20 to 70.

If I was doing it over again, I might go with a mini split and a seperate keroseen heater, like a hotdog. The kerosene heater just to get it comfortable quickly in the winter and the mini split to maintain heat and cool. Keroseen burns pretty clean with very little CO, so does propane.

I've tried a 200k btu hotdog in my garage before, it's so powerful you can basically start working as soon as you turn it on.

 

[ghnl]

The mini-split units are heat pumps (some have back up electrical heat). Heat pumps are not very efficient at supplying heat when outside temps are below 30F.

I have a mini-split in our garage. I like it a lot. Very quiet (just a fan running inside) and I don't really see an increase in our electric bill (it is not running every day however). Here in NC the A/C works fine and winter temps are rarely below 40F. But in Michigan where typical winter temps are a lot lower it might not work as well for heating.

 

[theoldwizard1]

If you have natural gas available, it will be hard for a mini-split to beat the cost to install and operate. Very few cooling days in MI.

IMHO, mini-split heat pumps work best and/or are most cost effective in small to medium sized, 1-3 room application and in an location that does NOT get much below 0F cold weather and a good number of cooling days (questionable in most of MI). 1 or 2 car garage, even with a loft is perfect. At about 3 car size (32x24) it becomes questionable whether the output of a single air handler can properly cool the whole area even with a auxiliary fan. The cost of a second air handler is not cheap.

They may make sense in a home where you do not want to heat/cool several rooms (unused bedrooms), because each air handler has its own control (when installed in the same large room the can be slaved together).

 

[bzinsky]

Heat pumps are not very efficient at supplying heat when outside temps are below 30F.

That was true 10 years ago, there are many options available now that are still very efficient below 0F. Anything with an inverter should still be efficient down to about 10 degrees, and still produce heat until around -15. Then there are some higher end models, such as mitsubishi hyper heat, which will still be efficient until around -5F, and then continue to produce heat until around -30F.

 

[bzinsky]

Also, man it is a weird feeling for it to be extremely cold out, stand next to your heat pump, and feel the air being blown out that's like 25 degrees colder than it is outside.

 

[Notgrownup]

Mini split but you should have a way of bringing it up to temp quickly like a torpedo heater or propane blower...then turn the mini split on to maintain. Them heat strips will burn a hole in your wallet at the end of the month...

 

[Jackfre]

You will not find an efficient mini-split with back-up electric heat. Any that will operate at lower temps will have a plastic housing and you cannot add elec strips to a plastic housing. I think a company called EMI may make one, but it has been some years since I've seen them.

 

[theoldwizard1]

You will not find an efficient mini-split with back-up electric heat.

We aren't talking about back-up electric heat. Some mini-split heat pumps do not require backup electric resistant heat.

Mitsubishi M - Series High Performance Hyper-Heat

 

[fastjohnny]

We aren't talking about back-up electric heat. Some mini-split heat pumps do not require backup electric resistant heat.

Mitsubishi M - Series High Performance Hyper-Heat

Post #7 is, but is, but incorrectly, as Jackfre pointed out.

 

[theoldwizard1]

Post #7 is, but is, but incorrectly, as Jackfre pointed out.

#7

Mini split but you should have a way of bringing it up to temp quickly like a torpedo heater or propane blower...then turn the mini split on to maintain. Them heat strips will burn a hole in your wallet at the end of the month...

The first part is correct (common for a garage with the heat set low/off to save money when not in use).

The second part is also correct IF you have a heat pump that requires heat strip. The Mitsubishi and other mini-split heat pumps do not.

They do require more frequent defrost cycles which is factored into that chart.

 

[bzinsky]

#7


The first part is correct (common for a garage with the heat set low/off to save money when not in use).

The second part is also correct IF you have a heat pump that requires heat strip. The Mitsubishi and other mini-split heat pumps do not.

They do require more frequent defrost cycles which is factored into that chart.

Yeah I think the older/cheaper non inverter heat pumps used the heat strips just to operate at colder temperatures. Pretty sure they only exist so that someone could still use them as their sole form of heat and not be left with a no-heat situation if it gets cold out. I don't believe adding the backup electric does much for total output and probably not going to get a space up to temp any faster.

 

[TwinFins]

Thanks for all the advice!

After reading thru the replies I think Ill stick with the forced air system. I have 240V near where it will be needed and natural gas within 10 feet.

Ill try to remember to post the results in a couple months when its all done.