Your learned opinion sought on heater sizing

[olytdi]

Hello heaterphiles,

Moving forward on my heating project and could use experienced recommendations with regard to sizing a NG unit heater. I've settled on either the Modine or the Reznor.

Disclaimer: I used probably six or seven BTU/heat loss/heater sizing calculators that came-up with recommendations from 25,000 to 160,000 btus. The discrepencies largly were due to limitations in the calculators or in variables I couldn't calculate (insulation, regional temps, etc.). I also read pages of "what size heater" threads which, interestingly, were more useful. Hence, I'm posting in hopes the variables can be "eyeballed" by those more experienced here.

This is a 28 x 28 square (800 square foot) pole barn sided and roofed with corrugated sheet metal and insulated with 1" to 2" fiberglass sandwiched on both sides in vinyl (vinyl wrap insulation). The R value is probably around 5 or so. The open truss ceiling is 16 ft at the ridge and 12 ft at the walls and also is insulated with the vinyl wrap. It is a square building.

There are two large sliding doors: 12 x 12 and 8 x 8. These seal poorly at the top and bottom but also are insulated with the vinyl wrap. There is one standard steel man door.

There are four windows with double pane glass and are about 18 square ft each.

The floor is concrete and is not insulated.

This is located in western Washington where it is temperate and rarely (but sometimes) fridgid. In the winter, it's typically in the 30's and 40's though down into the 20's at night happens regularly. I like to work in the shop at about 60 degrees so anywhere from a 20 to 40 degree temp rise is what will be used.

I have a ceiling fan mounted dead center that keeps air moving around the shop.

I'm aware of cycling issues with sizing too big but also don't want to wait a half hour to raise the temp. I hadn't intended to keep ithe heater on when not used but I've also heard that dead cold starts are where the wear and tear occur.

Sorry for the long winded post -- I just wanted to get all of the variables out there.

So what size are we talking here? Will a 45K do it?

Thanks up front!

 

[Mike007]

45K Will be more then enough. I have a 24 x 24 pole barn with an R30 ceiling and 1-1/2" polystyrene in the walls with sheet rock on top. I heat it with a 20K net BTU radiant tube heater. When I'm in it I usually set the stat at 60* which it maintains. Ive done this with the outdoor temp in the teens. Ive run probably thousands of load calculations. For some reason Ive found the program I currently use to grossly oversize garage heat. I think it's the roll up doors. The calc on my garage called for something like 100K BTU's.

 

[olytdi]

I hear what you're saying but your shop sounds like apples and oranges compared to mine. I'd like to think you're right, though!

 

[regguy1]

I have a 45K NG in my 26' x 30' 780 SF / 2 windows / 1 16' OH Door / R13 walls and ceiling. It heats the place just fine. You can see it in the video link below

 

[olytdi]

I have a 45K NG in my 26' x 30' 780 SF / 2 windows / 1 16' OH Door / R13 walls and ceiling. It heats the place just fine. You can see it in the video link below

Okay, so you've got twice the insulation, and fewer windows and doors. That helps me calibrate a little. Where is this located?

 

[Motofixxer]

Yep, a 45k should be no problem. A 75k is pretty standard size for many average houses. So realistically speaking a 45k is about perfect.

 

[olytdi]

Appreciate the input -- anyone else?

 

[regguy1]

Okay, so you've got twice the insulation, and fewer windows and doors. That helps me calibrate a little. Where is this located?

NE Ohio

The Mr. heater site had a calculator and it needed a total cubic foot number. with your high ceiling you might need a larger unit

 

[Mmfh]

I just helped a friend install a 75k Maxx heater in his pole barn, 30x40, a little bigger than yours but very similar in the way its insulated. This one only has one large door and one man door and a 30x30 window.

It was about 40 degrees outside when we fired it up for the first time, after about two hours we were at 60 degrees. We mounted the heater up high, probably about 12' off the floor, you can just barely feel the luke warm heat blowing at the floor level.

If you want to heat it quickly, I'd go bigger than what you are thinking. I've been looking at the Reznor units in the 100k range. I realize the problems with going to big, but I'm like you and want to turn on the heat, come back in 20 minutes or so and be able to feel it getting warmer.

Unless you are nice and tightly sealed up I'd go bigger than the 45k you are talking about. Twice that is what seems right compared to what I just did on the other building.

Mm

 

[olytdi]

Thanks guys, definitely sounds like I'm in the 45K-75k realm. Perhaps a 60K...