My question is, can one boiler be used to heat a detached shop floor (1600 sq.ft.) AND a 1225 sq.ft. basement floor that is 12 feet away? Also, how close does an indirect hot water heater need to be to the boiler? Could it be 15 feet away in another building? More detail... location is NW Montana, I will be working in the shop during the winter doing transmission repair, so roll up doors going up and down several times a day. The shop is being built first and the house follow 8 months later. Stick frame shop, ICF house, not planning on doing radiant heat on the main floor of house, just the basement. Thanks for any input or advice you can share.

Hi,
Yes no problem on building separation.
We design and supply these types of systems regularly.
Key is insulation, under slab 2" foam,
Walls more is better, r 21 , lid R 38+
Boilers more often than not these days are combi system, providing tankless direct hot water and condensing boiler function in the same system.
If the domestic side is for the residence place boiler in residence, if for the shop place there.
Domestic hot is isolated from the heat side so in your area a slight glycol mix might not be a bad idea,
Regarding the shop and open doors we do a lot with Tekmar slab sensors, generally a good all around stat but especially useful if doors are open often, Set at slab only will prevent the boiler from coming on and off due to air changes, stats can be set to slab, air or both.
If you need assistance we are happy to quote a package.
Good luck with your project,
Dan

Before you buy anything you should first do a room-by-room heat loss analysis so you can properly design the HR system in your basement and properly size and select the heat source. We have a free DIY heat loss analysis calculator on our website if you are so inclined.

The pipes going between the house and garage can be even farther then 15 feet, just insulate them, even if they are going through the ground. If the distance gets really long you can do a calculation for friction loses or you can just up size it.

Just so you know the garage floor will take like 4 hours to come up to temp. So you will not be able to go out to the garage, turn the heat on and start working in a warm garage. Some people leave the floors on low so they don't take so long to heat up.

Good luck....

Thank you for your replies. I ran the heat loss analysis tool and came up with 32,600 BTU/hr using a -6 degree 99% dry bulb temp and a desired room temp of 65 degrees. This was for the shop only. At this point my main concern is PEX tube sizing and spacing for the shop building. I know I only have 1 chance to get the layout right. The shop walls and roof will be done in about a month, the the floor after the roof is on, so I need to get the tubing figured out now. The house won't get started until summer, so I have some time before I have to size and buy a boiler and the rest of the controls etc. ( I wont be using the shop this winter) So here is my question... The shop side will be one zone theoretically since I want the same temp throughout, but with 1/2 inch tubing and a 9 inch spacing I end up with 2100 feet of tubing in a minimum of 7 circuits and a calculated head pressure around 21 feet. That sounds like way too much head to me but WTFDIK? Is there a recommended max head pressure per zone/pump? And if so, is it then necessary to split a zone into 2 zones or more in order to keep the total amount head pressure within limits?
The more I learn about this stuff the more I realize how much I don't know. I thought that adding hydronic heat was going to be relatively simple, and the free estimate/quote I got off of a website is looking more and more like a one size fits all we'll sell you a bunch of stuff, but no guarantees on how it will work when you get it done kind of thing. That is not what I am after. Any enlightenment you can throw my way will be greatly appreciated.

Your head pressure is off,
typical would be .5-.75 GPM flow per loop
Head about 7 feet for a 300' 1/2" pex leg
so if by some remote chance i'm right
7 x .75 gpm = 5.25 total GPM
Heat 7 feet
this would be a no information estimate, but it fall in the norms of a insulated slab system.
Good luck out there in these strange times
Dan

In floor heat isn't that hard (way easier than ducting in my mind). In a thick large stab the heat is going to spread out on its own. On a inch thick slab is a little more exact. I think keep you loops under 300 ft and spaced around one foot apart and you will be fine. The rest is above ground and can be easily modify'd/tweaked if needed. I recommend a Ecobee therm with a 24VAC relay to turn on and off the pumps. My house has been so much more stable since I switched over to Ecobee, no more over or under shooting my temp set point.

Good Luck

As others have advised, a 12" spacing, 1/2" O2 barrier PEX, circuit lengths less than 300' and using appropriate design circuit flow rates and supply temperature will work fine for this simple HR system. A heat source with outdoor temperature reset and any good thermostat that uses slab temperature feedback will eliminate all under and over shoot indoor temperature control issues. We like the Uponor 501S. Get a manifold with circuit balance valves so you can set the circuit flow rates to the design flow rates. And do a proper HR design to determine the design flow rates, maximum required supply temperature, and select circulator pump and heat source. To learn more about HR system design, perhaps get a copy of Modern Hydronic Heating by John Siegenthaler.

Thank you all for the info. I got a copy of Modern Hydronic Heating and have spent the last week reading it. My brain is fried. It's been 40 years since I studied algebra, and for the first time since then, I wish I paid better attention. But, thanks to software I don't have to read up on algebra too. I am going to get the 1/2 inch O2 barrier PEX laid out and spend some time this winter working out the rest of the details, or I will pay someone to do it for me. I will take a stab at designing the system myself with the software, but if it doesn't go well I will pay a professional to do it.

On a side note, The John Siegenthaler book can be rented in digital format for 6 months for $21 online. I highly recommend it to anyone who is trying to DIY a hydronic heating system. 700 plus pages of information that answers all the questions you might have about system design and how it works, or how it wont work if you mess it up. I have read them all this week, much to my wifes disappointment, but she will appreciate the warm basement when we get done!