Needed BTU's for heating a shop

[Jeff Monson]

I'm trying to decide on which boiler size and brand to put in my shop that I'm just completing. The shop is 40 x 60 with 12 foot side walls, I have 2200 feet of Pex in the concrete already. I have been looking at a LP 157k Laars Mascot combi boiler that can be used for the floor heat and for hot water that I will need in the shop also. Looking for some input if this is the correct BTU range and input on a good unit to install.

[Clark Hussey]

There are so many different variables for correctly calculating proper size BTU. Such as number of windows, doors amount of insulation, what area your located in etc. I would take all that information to a supply house. They should be able to calculate it for you.

[Jack Frederick]

Living in ND, you need a lot. There are online heat loss calculators that you can run. I think you could get by with 120k, BUT, the hot water then becomes and issue. How much HW do you think you will need? All of the combis that I know of are modulating. An important factor is the Outdoor Reset Program. Is it built in to the Laars. Clark's suggestion of going to the supply house for some assistance is a good idea if you are buying the product from them.

[Jim Becker]

I agree with getting professional sizing advise from the supplier to insure you have the capacity you need to heat adequately in your geography in addition to providing the amount of hot water you anticipate needing. You want to get it correct the first time for obvious reasons...

[Carl Beckett]

There are online heat loss calculators that you can run.

This is the only answer, either DIY heat loss calculation or by a professional. One I used I think was called 'slant fin'.

If you undersize it cannot keep up. If you over size, it cycles too often which is inefficient ($$). Outdoor reset and programmable controller does help. Variable production/capacity matching makes a difference. Hot water production on a boiler can be a big hog if not done well - zone it with a separate Hx in the HW tank (sure store tank or similar)

When I did all this to my own home a few years ago, my consumption dropped by 40% (it was remarkable!)

[Bill Dufour]

And what about calculating cooling with a heat pump as part of the ehating system.
Bill D

[Andrew Seemann]

You might want to have someone familiar with in floor radiant heat do the calculation and recommend a unit. You can do an online calc to get the heat loss easily enough, but that heat-the-slab-to-heat-the-shop thing is kind of an odd duck compared to your basic unit heater set up in terms of control with regards to water temp, cut in/cut out temps and times, etc. Usually there is a fair amount of engineering that goes into that kind of system.