Mini Split A/C Only or w/ Heat (+ Radiant)

[farmerisland]

First time post after lurking for about a year. New construction building an attached garage addition with mud room/breezeway transitioning to the existing old brick house. Garage is 28x38 OD and with the mud room transition it's all about 1115 sq ft radiant heated concrete. Garage won't be used as a shop, as I already have a gigantic one on the farm yard right nearby. It'll be used for some living space usage, gatherings, etc. Fully finished insulation, drywall, recessed lighting, etc. I want to keep it comfortable enough in both summer and winter. I live in Northern cold climate (think MN) so as hot and humid as it gets, winters are more extreme.

I am planning on ceiling fans, but the plumber convinced me a mini split A/C wall unit is the way to go in addition, for making the space quite comfortable. I had honestly never heard of these units before this past week, but they sound very efficient and a great option. With new construction, should I be looking at something ducted instead though? What type of mini split and sizing would be best? It sounds like I can get a unit that'd be one box outside and two interior "hoods", or just go with one?

And maybe my biggest question, aside from what size and brand of mini split unit, is would I just want an A/C only unit (what the plumber has initially mentioned) since I already have radiant floor heat... Or is it a no brainer to get a unit with heat too for supplementing the radiant? I have no experience or knowledge on efficiency comparison between the systems, but I should note for you that we don't have NG out here, so the Navien condensing boiler will be propane. Our electric out here is cheaper than avg, at $0.13 kwh.

Any other side suggestions or thoughts would be much appreciated too.

 

[chinboys]

Find a trustworthy HVAC-R company or an independent energy expert to perform both a Manual J calculation for heat and cooling based on your location, site orientation, and insulation values. Then get a blower door test to verify how badly your garage leaks outbound and inbound air.
Decide if you want to fix the energy loss problems or pay monthly for gas and electric bills and having a larger cooling system.

Use a ceiling fan as this device will make it more comfortable both in heating and cooling modes to circulate the condition air.

Look for a high SEER value system. A heat pump will also make heat in addition to cold air.
Heat pump systems usually have higher SEER values relative to mini-split systems.
You can have a mini-split or heat pump drive an inline air handler to distribute the conditioned air using a proper blower fan motor or install a couple of wall-mounted evaporators.

 

[u3b3rg33k]

I can't imagine paying for an HVAC contractor to install a minisplit, and then to skimp out on the reversing valve and not have the heating capability.

 

[dsimatt]

You will never regret getting the heat option. Our house is baseboard heat, in the shoulder seasons the one 18k btu mini split will heat the house up faster the they do.


If I had the money to build a place we would do what you are wanting to do with the garage and would run 2 mini splits solely 8 months of the year.

 

[farmerisland]

You will never regret getting the heat option. Our house is baseboard heat, in the shoulder seasons the one 18k btu mini split will heat the house up faster the they do.


If I had the money to build a place we would do what you are wanting to do with the garage and would run 2 mini splits solely 8 months of the year.

Thanks for the insight. Do you know of any value in running two interior wall units vs one or any other comparative setup for a 1000 sq ft garage space?

 

[American Locomotive]

I would think a single 12,000 BTU unit would cool that space provided it's well insulated, and provide adequate supplemental heat in the winter (assuming you buy a hyperheat unit). You could bump up to a 14,000 - 18,000 BTU unit if you wanted more headroom, but the smaller units are typically more efficient.

The old school "rule of thumb" was 12,000 btu for 500 sq ft, but that rule seems to date from the 1970s when plenty of homes had literally zero insulation.

 

[dsimatt]

Thanks for the insight. Do you know of any value in running two interior wall units vs one or any other comparative setup for a 1000 sq ft garage space?

To me it’s about more even distribution, two units can control the temp at a lower speed that one having to push all the air. We have a hyper heat in our house that puts out a lot of heat but then also pushing lots of air to get there, that makes it feel cooler than it is.


Not apple to apples but one unit in our house we freeze the living area but the other end by the bedrooms you feel the temp difference.