Hi, im trying to figure out what circulator I need for my radaint floor. I have a 32'x41'x6" concrete floor in an older red iron building with the 12" insulated panels that lock together. The building has 10ft high walls with some Batt insulation and a tin roof. The pex is about 3" below the surface.There is 2" insulation under the concrete with a vapor barrier.There are 4 circuits of 1/2" nibco oxygen barrier pex two are at 150ft and two are at 360ft. I have a 105,000 btu propane crown cast iron boiler.

Selecting a circulator is normally the last step of the HR system design process. First you accomplish a room-by-room heat loss analysis to determine the required heat gain that the HR system must provide to each room given the local climate design condition. Then you determine the circuit spacing, circuit lengths, circuit flow rates, and circuit supply/return temperatures that will provide the required heat gain to each room. Once you know the total flow rate that is required and the resulting system head, you can then select a pump that places this flow rate and head near the center of the circulator performance curve or Best Efficiency Point (BEP). Anyhow, this is how you would select a low cost single speed circulator. There are also higher cost smart circulators that can adapt to a range of HR systems and HR system conditions. 1/2” PEX circuits should not exceed 300’ length.

Unfortunately I jumped the gun and got some bad advice when starting this project. I didn't realize HR system designs were as complicated as they are. This is a shop so its one room. The circuits are already in and the concrete poured. I have 2 lines that run 12" from the edge of the of the concrete and along the parameter of the concrete. They are 12" apart and 150ft runs. Then I have 2 lines that run in the center at 360ft they zig zag and there is 12" of space between them. I used the following website https://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf to try and figure out the pump size I need, but im having some trouble. I got 5.4 GPM with 32ft of head loss. So I was thinking about using the taco 009. Is this right or?

If I understand you correctly, you have 1020’ of total PEX in the slab using 4 circuits (150, 150, 360 and 360) spaced at 12”. If I use the hydronic radiant floor heating software on our website, assume your total building heat loss is 20,000 Btu/h, assume design temperatures of 70/26F, assume a delta T of 15F, your maximum required circuit water supply temperature is 100F and you need a total flow rate of 2.7 GPM which results in a system head loss of 25.4 feet. So I think you need to refine your calculation somewhat, but there should be plenty of circulators that will get the job done. Perhaps use the software on our website.

Over thinking.
You have 4 loops
Grundfoss 15-58 will get it
009 is way to much, we call that the out board motor, or Fred Seaton special, like 12 gauge, kill anything close.
If you want to fine tune the disparity between the 150 foot loops and 350 foot loops get a lazar thermometer. Set returning water temp equal.
Relax, find what ever libation you like sit back and say, Job well done!
You did it with out experts,
Best regards
Dan

Make sure you have a manifold with flow meters and balance valves. The 150’ loops will have the balance valves mostly closed. The 360’ loops will have the balance valves mostly open. The design flow rates for the 150’ loops are 0.39 GPM each and the design flow rates for the 360’ loops are 0.94 GPM each and you will use the balance valves to achieve these flow rates. It is the act of balancing your vastly different loop lengths with the balance valves that is driving your system head to this high a level. If you don’t care about maintaining an equal Btu/h/sf heat gain gradient across the floor, you can just do what Dan suggests. Just select a circulator that can deliver about 2.7 GPM at 25.4 feet of head toward the center of its performance curve if you want the uniform heat gradient.

And why would setting return water equal based on real temperature not be an equal to or better alternative to flow gauges?
Establishing equal delta T across all 4 loops. If all return at more or less the same temp, flow then is based on actual heat loss.
Not saying I do not like flow gauges, we sell a type attach to the manifold so if they fail or need to be serviced loops can be isolated and they can be removed with out comprising the manifold.
But for fine tuning I see thermal adjustment superior.

How would I go about finding the total building heat loss. I used a calculator and got around 54000 BTU's?

Thank you for your help!

Dan, the above flow rates are for a 15F delta T across all loops for 20,000 Btu/h. If you are going to use the same supply temperature for all loops, you need to achieve the above flow rate ratio to achieve that delta T and uniform Btu/h/sf. So you need to generate about 2.4 times the flow rate of the 150’ loops in the 360’ loops. It doesn’t really matter how you do that...balance valves, hydro splitter, multiple pumps, etc. Using a manifold with flow meters and balance valves is likely the most common way to handle this situation and if you do so, you also need to account for the additional balance valve system head loss when selecting the circulator.

We have a heat loss calculator on our website that you can use too. If you like, I can rerun the design numbers using 54,000 Btu/h and assume 10% of that is exposed floor downward heat loss.

For 54,000 Btu/h you need 110F supply temperature and a circulator that delivers 6.7 GPM at 15.6’ head near center of its performance curve. The design flow rates for the 150’ loops are 1 GPM each and the design flow rates for the 360’ loops are 2.4 GPM each. Please note the loop flow rate ratio is still about 2.4. And 54,000 Btu/h for a 1,328 sf floor or 40.7 Bth/h/sf seems high to me.