Mini-split heat pump owners....satisfied??

[Throbber]

I have been researching these for a while now, and am about ready to buy, but have a question for all the owners. With this brutally cold winter, were you satisfied with the heating performance of your unit?

The garage I want to heat/cool is 1400 ft, with 12' ceiling, insulation is R30 ceiling, R19 walls, 26' of which is shared with my house. Twin 9x8 insulated doors (R6.5), and 5 windows (3'x5', not sure of R value, they are double paned). I am located in central Illinois. 100F in summer, -15F in winter this year.

I am looking at units by LG, Mitz, and Fujitsu. They are all inverter units that claim to have the ability to heat at low ambient temps. I am planning on using a 36,000 btu condenser with two 18,000 btu air handlers. The garage has three ceiling fans evenly spaced along its long axis (45') to help with air circulation. I want to keep the temps between 55-75 year round.

My concern is that I won't be able to keep the garage warm enough on the coldest days. I am still in the completion phase of the walls, so I can run a gas line and heater to supplement the heat pump if necessary. But it would be an added expense, and over 100' of line that is not exactly an easy straight shot out to the garage.

For those that have similar set-ups, does your heat pump keep up? should I run the gas line and supplemental heater? Or do I need to rethink/resize my whole system??


Thanks in advance

 

[Rockhead261]

You have gas available? Use it.

I tried getting away with an 18K BTU Mitsubishi Mr. Slim heatpump in my basement. Didn't work out well. Best it could manage was mid 50's when it got real cold, and the unit ran all the time (I'm in NY). I supplemented it with some electric heaters for the first year, then installed a Rinnai wall furnace that vents outdoors. Killer. Still use the Mitsu for A/C and it works great, but haven't even thought of it as a heater in ten years.

 

[Todd.Brock]

I know that they also put heat strips in to supplement the Heat pump function. Have you called an HVAC company that could recommend a system for you?


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[papasmirf]

I'm an hvac contractor from Oklahoma. My advice is use them for cooling and find a 95% efficient gas furnace or heater and go that route. A 100' of 1/2" or 5/8" gas line and an hour or so with a trencher will be $$$$ better spent in the long run.


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[Jackfre]

Pay close attention to the specs on each manuf mini-splits. I will use Fujitsu as an example as I know them best. You want a 36k but condenser driving two 18kbtu evaporators. The seer on that system will be 16, hspf 9.4.That system will heat down to 14*. It will actually go lower, but the output drops and 14 is what their literature says.

If you look at individual 18 units they will run at 19.2 seer and 10 hspf. Heating temp range from 5*upwards and output is from 7-29 kbtu. If you go down to the 15RLS2 ,model you jump to 21.5 seer and 12 hspf with outputs from 3.1-23.9 kbtu. That 15 is rated down to -5*. Fujitsu have a new unit (15RLS2H) out this year that will operate down to -15 at 21.5 seer/10.3 hspf. output range 3.1-23.9 kbtu

I would suggest that you go with one 18 kbtu unit or possibly a single 15. Put it in the most critical area in the shop and work the hell out of it. These are the ultimate in zone control so what you do is define the cold spot(s) and you can treat them the following year. You may find you don't need the second

I was originally going to go with a triple in my home. Once I priced up the triple I found it better to go with a dual 24 for upstairs bedrooms and install a stand alone 25 seer/12hspf 12 downstairs. We rarely run the upstairs units but I run the 12RLS downstairs for heat all the time.

I also run the Rinnai Energysavers that Rockhead spoke of. I think the ideal combination for you would be the Rinnai EX38 and one mini-split. That allows you to size the heat with gas and you don't need the super low heating spec for the mini-split.

I will say that even if you don't run the gas line to the garage, rough-in the gas lines for the building. Pressure test them and then you have options.

 

[theoldwizard1]

For those that have similar set-ups, does your heat pump keep up? should I run the gas line and supplemental heater? Or do I need to rethink/resize my whole system??

Unquestionably you are going to need supplemental heat, but not very often. I would probably install a propane/gas wall furnace and use and outdoor thermostat to simultaneous turn on furnace at about 10-20°F and turn off the heat pump.

The gas versus propane is the big issue. The gas line would be expensive. Check with a couple of local propane companies and see what the charge for 100 lb tanks, delivered. You need a minimum of 2, 3 would be better. They would likely be able to hook you up with a manifold and an automatic selection valve. 100 lb tanks are too big for the average person to haul around. A full 40 lb tank weights about 75 lb.

The biggest downside to this kind of setup is make certain that the tank going back to truly empty. The simplest solution is make up a transfer hose. and connect the 2 tanks together. The receiving tank (spare 20 lb) needs to be put in an ice water bath and the sending tank should be warmed.

 

[Throbber]

Thanks for all the replies. Looks like I will probably go ahead and run the nat gas line to the garage and use it for heat. The garage is attached so no trenching necessary, it's just a PITA to run the line where it needs to go and I had hoped to avoid it.

I still believe I will go with a twin 18k setup with a multizone condenser, even though it won't be as efficient, to ensure that my cooling needs are met. I listed 75F as the top of my range, but will probably run it closer to 70F, as I like it cool. I also want the multizone capability, as down the road I would like to add a small (6-9k) air handler for occasional, supplemental use in a home theater room. I prefer the multizone setup over multiple individual units. Don't really care to have several condensers hanging on the side of the house vs only one. Again, I do realize I give up a measure of efficiency doing it that way.

I do plan to install the units myself and have an HVAC guy come out and make the final connections. Partly to save on installation costs, but mostly because it's just rewarding to do it myself, and hey, that's why we come to this forum!! Lol!!

Now I'll have to start researching gas heaters. Looks like more time on the GJ!!