Small shop/storage building
hello, I am repurposing a pole shed from a grainery to a shop/storage building. 20’ x 40’. Existing concrete slab, except for a 5’ x 20’ section by an outside wall.
Building will have 2-10’ overhead doors and be insulated with closed cell insulation 12’ sidewalls heat loss of 60,000 but was calculated. A space ray 2 stage radiant tube heater is being considered for the heat source.
Is it worth the effort to install infloor in the small new concrete pour and consider adding hydronic radiators for the rest of the necessary heat load. I know it would require a mixing valve for the floor and leaving a higher water temp for the radiators. I have several large cast iron radiators save from a salvage project that have been sand blasted and painted.
There would be a work bench on the new concrete portion so the heated floor would be nice in that area. My other shop has in floor heat as it was all new concrete. It is very comfortable in that building.
I do not have much knowledge of the radiant tube heating system. I have only experienced it a couple of times in my career in the trades. It seems cost effective as far as initial cost. Just curious if it will provide decent performance in adequate heat.
im in rural Wisconsin. Lp is my current fuel, natural gas was just installed along our road so it is a possibility to go with natural gas.
Thank you in advance for your knowledge.
Comments
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what are you using this space for? What type of work.
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800 square ft total? I'd expect a load around 16,000 BTU/hr, Guesstimating 20 btu/ sq. ft.
Any way to over-pour the entire space with a floor radiant system?
If not, I have done shops like that with ceiling radiant. In one case exposed aluminum transfer plates with copper tube snapped in. You get the same radiant effect as floor heat and it will warm the floor to some extent.
With a load like that look at just a 40 or 50 gallon gas or LP water heater.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
I wouldn't even think about messing around with radiant floors in a building like that unless you're willing to hammer up the entire slab and properly insulating below the new slab. Radiant tube with a 12ft ceiling isn't ideal either, as you'll have a scorching hot spot directly below the tube. Your heat load is nowhere near 60k, probably closer to 15k but definitely not more than 30k unless the doors will be open all winter. Personally, I'd just hang a 30k Hot Dawg in the corner and be done with it if you're not willing to start over with the slab.
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Just so you know if you use any type of radiant heat you have to leave the heat on. They are not on-off systems. Depends on the occupancy and what the use is.
Use gas fired radiant, no worries of freezing or using glycol etc and will be cheaper.
Just make sure you have enough ceiling height to use the gas fired radiant
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the building will be used for heated storage of skid steer and small sub compact loader tractor, to keep warm for the cold months. Work on small equipment, Change oil,minor repairs etc.
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I did not do the heat loss calculation myself. It was done by the salesman from the radiant heater company. It was specified to be a 2 stage gas valve for what he was suggesting a 20’ unit centered in the building.
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that’s what I needed.
AVOID any open flames in the space.
a hotdowg with outside air will work fine
in floor radiant to warm the floor works well but ONLY to warm the floor.0 -
The decision for me would be based on how often I would be working in the shop. Cold concrete floors really drain you energy. If in fact you spend time out their overhead radiant would be a good option. Quiet, clean, faster responding.
The over head radiant tubes heat well, when you are directly under them, not so well when you move to the outside walls, away from their line of site.
FA unit heaters drive me nuts with the fan noise.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Again, if you set back the heat radiant will not be so good. At a constant temp they are great.
I might suggest a strip of radiant large enough to keep the space at say 45-50ish degrees. This will keep the slab at least warmish. Let that operate off a stat call it first stage
Then have a unit heater to boost the temp up as second stage when you are working out there.
The shop I worked at originally had gas and ac roof top units. When the units got old the ac worked but the heat exchangers were starting to fail.
We disabled all the roof top heat and kept the cooling and installed gas fired radiant it was a 100,000 square foot shop and it worked great.
Noticed a big difference in the winter.
One big advantage was they used to park 15 trucks inside the shop at night. In the morning all the trucks went out and with the rtus and the 12 x 12 garage door opened it would take a long while to recover.
With the radiant you open the door and move all the trucks the air temp was freezing as soon as the door was shut within 5 min you were warm as the slab was a huge radiator.
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thanks for the input.
My larger shop has infloor radiant that I installed, but that was a new concrete slab. Easy to do. Very comfortable working in that building. This building has an existing concrete slab in good condition, so not an easy choice.
scorched air heaters are cheap to install but are drafty and noisy. may be a good option here.
I do not believe in set backs, takes too long for recovery, results in less comfort. (I still use some of my old mercury thermostats in my house that run cast iron radiators.) Especially if I use the hydronic and large cast iron radiators I already have. I just need to find a small enough mod con for the proper heat loss of the building, if one that small exists.
I will have to run some numbers0 -
You can get a 55k mod con that will turn down to around 8,000 btu/ hr
I have a similar sized shop in Utah, 15k load with a Lochinvar 55k boiler locked at 18,000
The least expensive option will be a gas fired unit heater
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Can you find some older cast iron wall radiators?
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Pole buildings are notorious for being hard to insulate, I would believe the 60K BTU/hr load in Wisconsin.
I don't think floor heat is a good match for this application. I think you'll want something where you can warm the space quickly when you're in there and let it cool off when you're not.
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75 BTU/SF isn't believable anywhere besides a tent on Mount Everest… And no, pole buildings have not been hard to insulate since about 1980.
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I don't know where you're getting "pole buildings haven't been hard to insulate since 1980." But let's model this building.
Let's say the design temp is -10F, that seems to be where most of Wisconsin lies. So 80F below room temperature. Building is 20x40.
One wall with two doors, let's say an average of R2. That's 12' high by 20' wide, 240 square feet. At 80F drop and R2 that's 9600 BTU/hr.
Three walls with spray foam, let's say R12. That's 100 linear feet, 1200 square feet. 8000 Btu/hr.
Spray foam on the roof, also R12. Roof is 40% more than floor area, that's 1120 square feet. 7500 BTU/hr.
Floor is uninsulated concrete, R1. Let's say it's 40F below the slab, so 30F drop. 24,000 BTU/hr.
Those roll up doors are going to be leaky, let's say 15 ACH50 or 0.75 ACH natural. Building is 9600 cubic feet, so 7200 CF/hr or 120 CFM. At 80F that's 9600 BTU/hr.
Add them all up and you get 58,700 BTU/hr.
And I didn't start with the answer and work backwards. I started with what I thought would be reasonable given OP's description.
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And if the thermostat isn't left at a constant temp you will need more BTU to get out of set back. On the other hand a work storage area may not need to be kept at 70 deg.
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agree. At -10 outside, 50f inside is nice especially with coveralls and such.
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And you made up that entire system to fit your agenda as well as did the math wrong. There are no roll up doors, he has overheads. Nobody spraying foam (which is literally the easiest there is) is only spraying R12 on a ceiling (or walls, for that matter). 70* indoor for a storage space is ridiculously high, and the uninsulated concrete will never have a 40* average below if the space above is kept at 70*.
So to start over with more realistic figures but still leaning toward your benefit w/ 80* diff, we have:
-1187 sq ft of wall at R14 (2" minimum closed cell) = 6783 BTU
-800 sq ft of ceiling at effective R38 (again, bare minimum and unrealistic) = 4571 BTU
-200 sq ft of insulated OH doors at R8 + walk door and 4 four 2x4 windows at R2 = 4520 BTU
-120ft of uninsulated slab = 9600 BTU
-.75 ACH for 9600 CF = 10,368 BTU
For a grand total of 35842 BTU at -10* outdoor with 70* indoor. Now we drop that indoor temp to 60* and move the ceilings to a more realistic R38, we're at 28,482.
Being in this climate and doing heat loss calcs every day on buildings like this, nothing with a layer of closed cell comes anywhere near 75 BTU/SF. Half that is excessive 99% of the time.
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the overhead doors will be raynor 3”thick commercial doors. R-10.
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When folks throw out those design numbers that is for the most severe days. Good chance 90% of the heating season you are above those design temperatures. I know our location in Milwaukee has been way above design most of this winter.
If you hit design or below, the room drops a few degrees, not a huge issue for shops that are used occasionally. Stay home those days:)
I worked with two different Mennonite construction companies in Missouri, installing radiant, that did only pole barns. There were many levels of insulation options they offered depending on the buildings use.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream2 -
@hot_rod : "Good chance 90% of the heating season you are above those design temperatures."
By definition 99% of the time should be above design temperature, it's the 99th percentile.
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