Mini split heat pump vs forced air

[jack anderson]

Greetings,

I have a two car detached loft garage 30' X 28' 10' 4" ceiling.. I framed in 2X4 walls on all the walls downstairs. 8/12 pitch. The walls are insulated with R19, Ceiling is insulated R38 with sheet metal covering, The loft knee walls are R19 as is the loft ceiling rafters. The roof is sheet metal. The loft area is 12' X 26'. I have put in a 5' Andersen French door in the loft going out to a deck and a window on the opposite side. I have been considering options to heat and cool the upstairs. I am leaning towards a Fijustsu Mini spilt system but I also have other options to consider such as putting in a forced air propane heater like a Hot Dawg or Renzor etc. and the putting in a 14,000 BTU window AC upstairs... If you have been down this road please give me your opinions of a mini split vs forced air etc. I live in central Pa and I don't plan on being in the garage all the time and would like the ability to regulate the temperature.

 

[ghnl]

We have forced air in the house. I installed a pair of ductless mini-splits in the garage & bonus room above.

I like the mini-splits. Clean & quiet. They are quite efficient - we've hardly seen an increase in the electric bill (but they are not used every day either). Heat pumps do lose some efficiency at very low temps (below 20-25F). (I bought units with back up electric heat but that is rarely needed here in NC.)

The only thing I wish they had is a lower set temp for heat in the garage. I sometimes want to just keep it on 45-50F on a cold night so the garage isn't stone cold the next morning but these only go down to ~ 60F.

 

[turbowoodworker]

I have to agree with Eric in NC. My experience is limited as I am in the permitting stages for my house and shop in Chatham County NC. My builder has lots of experience with the mini splits and has made that recommendation to me. I think Mitsubishi makes them too. The only other consideration would be nat gas but that is not an option in my community. Good luck and let us know which route you choose. Rick

 

[JakeKohl]

We have forced air in the house. I installed a pair of ductless mini-splits in the garage & bonus room above.

I like the mini-splits. Clean & quiet. They are quite efficient - we've hardly seen an increase in the electric bill (but they are not used every day either). Heat pumps do lose some efficiency at very low temps (below 20-25F). (I bought units with back up electric heat but that is rarely needed here in NC.)

The only thing I wish they had is a lower set temp for heat in the garage. I sometimes want to just keep it on 45-50F on a cold night so the garage isn't stone cold the next morning but these only go down to ~ 60F.

The units that use 410A are more efficient at lower temps than the older R20 systems - I've read that you can expect them to be able to reasonably heat a space down to 5 degrees F outdoor temp (but... that sounds a little far-fetched to me).

I have an LG 18k btu unit in my 24x36 garage and another in my 24x36 second floor. They really work very well and easily cool each space. My only complaint, like yours, is that the thermostat temperature in heat mode doesn't go down below 60 degrees F. I would like to just normally knock a little chill off the air downstairs and keep it from freezing unless I'm planning a long work weekend in the garage.

Mine have an option for a wired thermostat but I haven't had a chance to check and see if it allows them to be set lower (I doubt it since most of the brain power / probes resides in the unit itself).

 

[thammel]

I'm in a similar boat. I bought a reznor UDAS to run off propane. Then I plan to get a mini split heat pump and have the reznor kick in once the outdoor temp gets to about 35F. This should get me the best of both worlds with a hybrid system. Honeywell tstats have options for use of outdoor temp sensors to allow control of the system by the outdoor temp too.

Tom

 

[Jackfre]

I'm in a similar boat. I bought a reznor UDAS to run off propane. Then I plan to get a mini split heat pump and have the reznor kick in once the outdoor temp gets to about 35F. This should get me the best of both worlds with a hybrid system. Honeywell tstats have options for use of outdoor temp sensors to allow control of the system by the outdoor temp too.

Tom

In Maryland you will not need the Reznor back-up. The Fujistu's will operate at rated capacity, or very near to it, at 5f. You could rough-in for it but you won't need it.

 

[Highbeam]

In Maryland you will not need the Reznor back-up. The Fujistu's will operate at rated capacity, or very near to it, at 5f. You could rough-in for it but you won't need it.

That is so great. At 5 degrees they're still making full heat. Not your daddy's heat pump.

 

[drb007]

My understanding is that the Mitsubishi Mr. Slim heats down to -15 degrees. I have one in my shop in northern WI and have never had trouble keeping it 68-70 degrees all winter long. I have no backup heat souce. Love the heat pump. Very inexpensive to run. I personally would never go back to my HotDawg. Plus I have AC now too!

 

[RKA]

I put a Fujitsu in my garage last winter. I have a few simple observations.
1. These weren't meant for garage environments where you're trying to raise a 35F garage to 65F. That said, if you're patient, they will do reasonably well. However mine is in an insulated attached garage, which typically doesn't get below 35F when ambient is in the teens without heat.
2. Heat output is pretty good until ambient drops below 20F. Around that point heat output drops and the garage is cold enough that it can take hours to bring the temps up 20F. Electric usage also gets pretty high at this point. It would be nice if they allowed a lower set point, but that's been mentioned. As a result I just shut it off until I need it.

In a detached garage in central PA, I would consider using a small forced air unit to bring it up to temp quickly (and probably more economically), then let the mini split take over maintaining temps. If its below 20F outside, just switch over to forced air. You'll have to do some math to see if that makes sense.

All that said I'm still happy with my investment. I did get a small 15K BTU heater that runs on a 220v line in the garage to supplement on those cold days. It's not a lot, but it's something and it's not often that I need to use the garage on a day like that. It's also nice to have AC, which probably gets used three times as often as heat. The only gripe I have is this unit eats 270 watts continuously when it's off (summer and winter). For something that's is used one day a week, that means I kill the breaker when it's not in use.

 

[theoldwizard1]

I am assuming you are trying to heat and cool both the garage and the loft. I am also assuming that the loft is separated from the garage by walls, door(s) and floor.

Mini-splits are good options but they don't heat well.

A Renzor would heat the garage well, but it would take a long time to heat the loft unless you had some fans (and possibly holes in the ceiling/floor) to circulate the air from below to the loft. If you only want A/C in the loft, a window A/C is the way to go. This combination is probably the cheapest, but will require more "fiddling" to get things comfortable.


I would look into a forced air system with A/C, but you really need a 2 zone system. A bit more duct work and couple of dampers and 2 thermostats, but both areas will be comfortable.

 

[Crazy68Dart]

My understanding is that the Mitsubishi Mr. Slim heats down to -15 degrees. I have one in my shop in northern WI and have never had trouble keeping it 68-70 degrees all winter long. I have no backup heat souce. Love the heat pump. Very inexpensive to run. I personally would never go back to my HotDawg. Plus I have AC now too!

What electrical service does the unit need? Are these units affordable compared to alternatives?

 

[drb007]

The Mitsubishi takes 200, and I think a 30 amp breaker. The HVAC guy told me that it never draws more than 17 amps.
My dad has the Fujitsu in his house, and I agree, they can only heat down to 20-30 degrees. He has hot water to back it up.
In my shop, which is really not that well insulated, I keep it at 68, and I really don't have a hard time when it gets below zero. My heat bill (combined with my house, of course) was about$ 60/month more compared to the previous year during the coldest part of the winter.
Jackfre is the guy on this forum to talk to...he was a HUGE help in my decision making, and is a wealth of knowledge in this area.

 

[drb007]

Oh, and I paid $2300 for my unit, plus $300 for the HVAC to hook up the lines for me and make sure I did it right.
Very easy install.

 

[jack anderson]

Thanks for the response do you have a fujitsu system? One quote i got from a HVAC contractor was 6,200 dollars to install two zones one downstairs and one upstairs 12,000 btu's plus the outside unit. Thought this was a high estimate?

 

[drb007]

I have the Mitsubishi Mr. Slim. One indoor unit.
My dad has the Fujitsu, and has an upper and lower indoor unit. $4500 installed.

 

[jack anderson]

4,500 dollars seems like a reasonable price. What size units went in upstairs and downstairs? What is the Seer rating? What size is the outdoor compressor? The Unit I was quoted is for (1) 2 1/2 ton 17.5 Seer outdoor compressor system with 18,000 btu's for the downstairs wall mount and 12,000 BTU's for the upstairs. This would include some additional wiring and a 30 amp fuse etc. Once again the quote was for 6,128.00 dollars installed. I was hoping for a price near 4,500 dollars or so.

 

[jack anderson]

Greetings,
The contractor gave me an estimate of 6,900 to install a Fujistu mini spilt heat pump 17.5 SEER (air and heat) with the main unit outside and two units inside one 12,000 btu's for upstairs and one 18,000 btu's for the downstairs. He plans to run the lines outside the garage into the second floor. I was wondering if running the line sets into the wall vs. running the lines outside the wall makes a difference. I read on some previous posts that line sets should be run inside the wall? Does it matter which way it is installed? Also I thought the estimate might be high?

 

[ghnl]

Inside the wall is neater - looks better but could make a future repair problematic.

If run outside they should be inside line set covers. (Being frugal I used some plastic downspout.)

 

[Steevo]

What does the "inside" portion of these "mini-split" units look like?

Edit: Never mind, I Googled it and found them.

 

[JakeKohl]

Greetings,
The contractor gave me an estimate of 6,900 to install a Fujistu mini spilt heat pump 17.5 SEER (air and heat) with the main unit outside and two units inside one 12,000 btu's for upstairs and one 18,000 btu's for the downstairs. He plans to run the lines outside the garage into the second floor. I was wondering if running the line sets into the wall vs. running the lines outside the wall makes a difference. I read on some previous posts that line sets should be run inside the wall? Does it matter which way it is installed? Also I thought the estimate might be high?

Inside the wall is definitely cleaner but it is considerably more difficult and will involve interior finish work if the interior is already finished. I installed mine in the wall - and would do it again in a new construction situation...not sure if I would go to that trouble for an existing installation. Also note that if I do have to replace an indoor unit, it's going to involve opening up drywall and removing insulation.


DSC_3020 by Team Seacats, on Flickr


DSC_3027 by Team Seacats, on Flickr

 

[jack anderson]

Very nice install. What is the SEER rating on the outside unit? Also what size units are on the first and second floor?