Will a rinnai ex38 work?

[Soccer918843]

I have a 1500 sq ft shop, 28x52 with 10’ walls I have r23 in walls and r30 in ceiling I would of went more but have attic truss so only had 7.5” to work with. I live in upstate ny will a rinnai propane ex38 be too undersized? Or would I be better off going with a big maxx? How long would it take a rinnai to heat the space from day 40 to 65 if I kept it turned down majority of the time?
Thanks

 

[Firebrick43]

Fiberglass insulation or foam/cellulose? Insulation under the slab? Insulation on sides of slab? Air sealing none/ok/very good?

 

[Soccer918843]

Fiberglass insulation or foam/cellulose? Insulation under the slab? Insulation on sides of slab? Air sealing none/ok/very good?

All dense rockwool mineral wool no insulation under the slab or sides, every hole and crack has been spray foamed with a handheld can.

 

[nadogail]

IMHO, You need an engineering study that takes into account the number of degree days, the heating needs of the area to be heated, the human activity that will be taking place in the heated area and many other factors.

Without that information maybe you can find someone in a situation identical to yours and see if they are happy with your proposed solution.

 

[Showkey]

Or you can look at the wall chart:






It’s always a guesstimate ( compromise) as the choices are 30-50-70-100k in very round numbers.

38k might be just a little small, but will certainly work. Might be just a little slow to recover on very cold days.
50* setback is the recommended minimum temperature for most hanging garage heater. Cold intake is harmful causing rust and corrosion.
Agree on the ceiling R50 would have been better.
50k Maxx would work too and be half the cost of the Rinnai. Rinnai is high quality.$$$. The modulation burner is a nice feature. Cold air intake and more stainless.
70k would be quicker on the setback recovery.

Mine is similar climate 1000sgft R19 walls R50 ceiling with 45k had 70k that went out after 18 years. Build, insulation and 70k was prior owners choices.

 

[yeldogt]

My outbuilding space is about your size 1600 ... in PA ... 1/2 of the building is SIP construction. It's actually two buildings open to each other. The SIP side is very tight and the other is conventional. I did not build this .. but have built other SIP buildings. I can tell the conventional side is not as energy efficient. So my guess is together they have a load close to a new well built non foam structure. I have a 40k unit like what you want to use and it has no trouble heating the whole space. It's not going to have enough to raise a full space from 40 to 60 in short order .... I keep the space in the low 60's and bring it up when I'm going to work out there. The space also has a 4000k electric that I can flip on when I am away for a couple weeks and I drop it down a bit lower ... high 50's at the lowest -- I can arrive and turn them both on if I want to be out there right away.

Bringing a building up to temp takes lots of BTU's -- even more if full of cold tools and equipment. I'm on propane .... with a tight building -- it's not outrageous to heat. Also -- if you do that big of a setback very often 40/60 .... you are not saving all that much.

Most garage heaters are sized for more recovery ..... but you have to be careful and not go overboard as they cycle too much.

 

[Jackfre]

The 38 will handle it. Is it a push, yes, but the worst that will happen is when you get that odd sub-zero week the building will be cooler and you will wear a heavier shirt. Keep in mind that you only reach design conditions in heating about 2% of the seasonal heating hours. With the programmability and frost protection settings you will like this unit. Position it so the air circulates well.