Heated floor in new shop

Using a Viega pressure drop table ( http://www.viega.us/cps/rde/xbcr/en-us/TD-PF_1113_(ViegaPEX_Ultra).pdf ) it looks to me like you can expect to push more like 8 or 9 gpm with 11 feet of head using a low-wattage steep curve pump like a 15-58, 008, Alpha, or Stratos.

You'd only need a deltaT of 25 degF to get your 100000 btu per hour.

One small steep curve pump (like the ones mentioned above) will likely do the job of pulling flow all the way from the boiler and through the mixing valve, but you'll need another pump for the near-boiler loop that maintains return temperature protection for the boiler.

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Outdoor wood boiler? Assuming it's an "open" or non pressurized boiler, are you going to use a heat exchanger to isolate the tube from the boiler?
Antifreeze in the system?
To answer your question....any of the small wet rotors pumps will do what you need for the floor.

The thing that jumps out at me in your post is the heat loss. You are over 30 btu's per sq ft and that seems high unless the building insulation is minimal. What have you got going on there?
We have a 90,000 btu pellet boiler heating a 6,400 sq ft pole type structure with 8 and 16' ceilings in it here in Michigan. It has 2 16'wide x 12'tall overhead doors + 4 9'w x 7't on the low part of the building.

I thought the same thing, 100,000 btu heat loss is quite high for a 50x60 shop. You should be in the 60,000 or under range, especially with new construction.

Return protection is critical with any radiant (low temp) system and a wood boiler.

TS

We are currently building a 60x50 clear span steel building with 12' side walls and three 10x10 garage doors [3,000 sq ft]. ... the heat loss on the building should be around 97,000 BTUH.

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Compared to my shop building, your heat loss for IL appears to be very excessive. My building is 1,536 sq ft, 14' side walls, one 12 x 12 garage door, one 3' and one 4' service doors; 2" of foam under the entire floor and perimeter insulation; 6" fiberglass in the walls and 12"+ blown in fiberglass in the ceiling -- similar to your building but 1/2 the size. My calculated heat loss was about 35,000 btuh at -35F. Actual heat loss in the +10 to +25F range is around 12-14,000 btuh; highest recorded 24 hr heat loss was about 18,000 btuh in the -5 to -30F range. Building is maintained at a constant floor temp of 61F.

Glycol in the floor, 1/2" pex on 12" centers in 5" concrete; flat plate heat exchanger with mixing valve to supply the floor with 100F water and up to 190F boiler water; 6 loops at somewhat under 300' per loop. 1000 gal of hot water storage; normal boiler burn 4-6 hours every other day.

jebatty said:

Glycol in the floor, 1/2" pex on 12" centers in 5" concrete; flat plate heat exchanger with mixing valve to supply the floor with 100F water and up to 190F boiler water; 6 loops at somewhat under 300' per loop. 1000 gal of hot water storage; normal boiler burn 4-6 hours every other day.

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That kind of data can't be had anywhere else! Real world numbers from real people, thanks Jim! This is why I keep coming back to Hearth, you cannot replace people like jebatty.

TS

If you intend to run the boiler water through the in-floor pex, then a plate hx is not needed and the mixing valve is all that is needed. I decide to use glycol in the floor (50/50) because I wanted 0 chance of freezing in the floor and the potential of a leak, although I use tap water treated with appropriate chemicals in the boiler and storage. With a mixed water system, the plate hx with a separate circulator was necessary. My storage is a re-purposed LP tank and there was no possibility of using a copper coil hx instead.

I would suggest a thermostat sensor buried in the floor to control shop floor temperature and not be too concerned about controlling air temperature. My controller is set to maintain the floor at constant 61F with a 1F differential. This results in sensor floor temp between 60F and 63F constant, no short cycling.

If you are concerned about shop air temperature, as I was, you could consider also adding a hot water unit heater to the shop to bring the shop air temperature up higher than the temperature maintained by the in-floor when you wanted warmer air temperature, and if so, you can stub in the plumbing connections to do this. The floor responds very slowly to changes in temperature, and trying to maintain a constant air temp can be a challenge with in-floor radiant. I stubbed in plumbing for a unit heater but never installed it. Keeping the floor at a constant 61F maintains air temperature from about 53F to 63F (T8 electric lighting adds some heat), depending on outside temp, which can go as low as around -40F where I live, although -5 to +10F is more usual during the middle of winter. The warm floor make the "feel" temperature for working in the shop very comfortable regardless of the actual air temperature.

Besides concerns related to efficiency and lack of smoke, another major issue I have with all non-storage hot water boiler systems that burn wood is the lack of hot water storage. As my post above mentions, I need to burn at most only once for 4-6 hours every other day to heat my shop. And that's during the coldest weather. Warmer weather might take a burn every 3-5 days or so. The ease of managing burns every other day for a brief period make wood heat very convenient. It is the 1000 gallons of storage, which I can heat up to 193F in my system, that makes this possible.

I don't know what OWB you are looking at or how much water it will hold, but at 65,000 btuh heat loss/demand, that amounts to about 240 lbs of seasoned 20% MC wood per day, and if the boiler water is about 300 gallons, then the stored heat in the boiler water (180-100F) is only a little over 3 hours of heat before you have to re-fire the boiler.

Regardless of the boiler, it will make a lot of sense to insulate very well and do everything you can to keep you heat loss low. I would not enjoy tending a boiler multiple times every day and night to keep a building comfortable.