Mini-split question

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ploughna

New Member
Apr 17, 2020
2
Pennsylvania
Hi all
As a new forum member I don't yet have enough privileges to put my question in the DIY mini-split thread a little further down so apologies for creating a new thread.
I've been thinking about one of the MrCool mini-splits sold by Costco and others for my workshop - the space has two cinder block walls (one of which is shared with my detached garage) and two stud walls, exterior vinyl siding all with no insulation. Area is 500sqft and an uninsulated sloped roof with asphaft shingles(7ft on one side and 11ft on the other). Roof is not vented. Concrete slab floor.
I'm looking primarily to cool the space in summer which in mid-Pennsylvania are hot/humid. It'd be great if it could heat in the winter too, but that's no so much a concern as the building does have a chimney that I can use for a wood stove if necessary.
Does anyone have an idea of what size mini-split will give me decent cooling - common options for these units are 12/18/24K BTU. I'm ran a number of calculators and was thinking 18K should be ok (even less if it were insulated). I know insulation is the way to go, but I'd prefer to suffer higher utility bill costs given my infrequent usage and insulation is not so straightforward or cheap either (eg the sealed roof would preferably need closed cell foam between the rafters)
If I go too large (24K?), will I run the risk of 'short-cycling' and end up with high humidity, or will the mini-split variable speed capability avoid that? Are there limitations to the range of this feature?

Thanks in advance for any advice

Paul
 
Ideally, for dehumidification, you want the thing to run constantly so your heat gain from outdoors needs to fall within the modulating range of the apppliance. 12/18/24 are the max but they all can modulate down.
 
Thanks for the response - that makes sense. Any idea on what size unit would be best fit for the room I've described?

Ideally, for dehumidification, you want the thing to run constantly so your heat gain from outdoors needs to fall within the modulating range of the apppliance. 12/18/24 are the max but they all can modulate down.
 
First of all, you should get some insulation above your head. Do not even try to heat with a mini-split without it. I would not do the 24k. 18k but with some insulation you could do the 12k. You are not looking to get it to 72 degrees.. 76 and dry will feel a whole lot better than what is outside, with that said it sounds like you have some insulating and or hole plugging to keep the moisture out.