I am trying to figure out which circulator to go with... Here are my specs: 2,186 sq ft house, dedicated Tankless water heater on a closed loop, 38,000 BTU heat load, 1/2" pex @ 300 ft loops, 10 loops, planning 2 zones, Will a single TACO 007E-F2 007 ECM HIGH-EFFICIENCY CIRCULATOR suffice? Will i need multiple pumps? Can/should i make my loops shorter and buy a corresponding manifold? I have options as the system isnt completed yet. I have bought the 007e-F2 already and im not certain i should i should install it.Thanks in advance.

That pump is rated at 16 gpm max. If you are going with at least 2 zones then use two pumps if you want to control the zones independently. If you want to use one pump and control 2 zones independently then you will need zoning valves which are almost the cost of the pump. (all don't know how you are plumbing the water heater though)

One pump in my opinion is to small for your house. Spread the <16 gpm across 10 loops you will get low flow which will cause the temp drop in the tube to be excessive and cause warm and cold spots in the floor.

I am not a expert and have only done 2 houses with all floors being heated with 1.5 inch concrete slabs throughout. Good Luck

Thanks for the feedback. Talked with a plumber today who suggested the same thing!

Most plumber designed HR floor heating systems are grossly over pumped. A 15 deg F supply to return temperature drop is a good goal. This can usually be achieved with about 0.25 GPM per circuit. As an example, we just did a design for 2400 sf home (4 zones, 8 circuits and 1683 feet of PEX total) and the total required flow rate was only 1.6 GPM. It is certainly true that zone actuators are somewhat expensive. So if you have too many zones, you are throwing away money. And if you have too few zones, you may have rooms that are hotter or colder than desired. This is why a room-by-room heat loss analysis is required BEFORE you can properly design a HR floor heating system. Consult John Siegenthaler’s “Modern Hydronic Heating” if you want to learn how to properly design and install a HR heated floor system.

Question is what is the head on the tankless water heater
Sailaway is correct in that the flow is minimal
But the head of a tankless unit plus head for desired flow are the keys
Then you can pick a pump,
We use Grundfoss Alpha as a base line pump on most of our fabrications. Generaly works well on all applications as it can turndown, is ECM, can be set to pressure so it you use actuators it will vary flow.
But again the head of the tankless, you need to assess that,
Dan

Yes indeed, one needs to know the head of the tankless water heater and the head of all the PEX circuits at the design flow rates...which should be the minimal flow rates that will move the required heat to each room as determined by the room-by-room heat loss analysis while keeping the supply/return delta T to 15 deg F or less for each circuit. The higher the flow rates, the higher the head will be...requiring more pump or multiple pumps...which is why designing for minimal flow rate is important. One can only properly select a pump once you know the system maximum flow rate and head that it will service. I would also second the Grundfos Alpha recommendation, but your existing Taco circulator pump may prove to be adequate as well. We have free DIY software and detailed instructions on our website to accomplish this design if you are so inclined.

I don't care for the lower flow rates because it creates hot and cooler spots in the floors. I have 3 speed pumps in one house and have tried turning them down to save pumping costs. Most of the winter it worked fine but when it was really cold out the floor heat was uneven and small pumping savings wasn't worth it to me. Worked fine and kept house warm, just didn't like it uneven.

In my new house I am using 5 Alpha's in Delta-t mode. Haven't used them over winter yet but have over the summer. I wish I could raise the minimum speed when running in delta-t mode, I have it where sometimes it isn't pumping enough and doesn't see the heater/cooler kick on and doesn't raise the pump speed up.

I have 2 geo units and have them both run together. One for the floors and one is for forced air. Thus I have been chilling the floor(1.5 inch concrete) hoping to get the house to coast through the mid day expensive electrical cost times and only cool the house at night.

Good Luck

If you adhere to the supply/return delta T of 15 deg F or less guideline, you are not going to experience a floor temperature gradient that is detectable with bare feet...especially a concrete slab floor. That’s the whole motivation for this 15 deg F guideline. Yes, you can certainly go much less than 15 deg F, but doing so results in increased system pump cost (i.e., using higher than minimum required flow rate results in higher head and more required pump capacity) and increased operational cost (more pump capacity requires more electrical power) for no detectable improvement in the floor temperature gradient.

Thanks, will have to look at the delta T temp in the really cold part of the year.

I think you might have your pumps mixed up,
The Alpha is not Delta T, it is pressure sensing, A great pump, but does not do delta T,
If you want Delta T look at the TACO 00e Series VT2218 circulator

That’s true Dan... Delta P would normally be the preferable smart pump control approach for most normal HR systems. I suspect that when he wrote delta T mode, he was referring to control logic in his GSHP system that essentially operates the pump to a delta T scheme, which would be appropriate and beneficial for a GSHP system? Or maybe he meant to write delta P, which is essentially how the Grundfos Alpha works?

Sorry I am running 5 Taco VT2218 VIRIDIAN's in Delta T mode. The slowest speed can't over come the built in check to get water flowing for the pump to see the increase in delta t. I have 5 separate parallel loops that all start and stop at the same point, so I don't think it could be caused by back pressure. Most of the time it works but sometimes only 3 of the 5 pumps will see the increase in delta t and cycle up their speed.

Wish the pump didn't have to see such a large temp difference to speed up. I am using a Geo water heater so I get about a 10 degree temp rise.

Newbostonconst, I may have been somewhat remiss in not fully addressing your floor temperature gradient concern/issue. For HR residential construction, you should also always use a PEX spacing of 12” or less to avoid floor temperature gradients. It’s ok to use a larger PEX spacing for commercial construction where barefoot comfort is not an issue. Using less than 12” is sometimes appropriate in areas that need more Btu/sf such as a corner dining room with large amount of windows relative to room area. Again, this is why a room-by-room heat loss analysis is so important before you can properly design a HR floor heating system.

I have always used a one foot spacing. I am also not talking about the floor being colder around doors and at the edges, I understand the heat load in those points are more.

I don't use continuous circulation. When a room calls for heat I turn on the pump to circulate hot water. Maybe that could be it. It is not that bad and most people wouldn't notice, but increasing the flow took care of it.

Well in that case, the minimum flow rate that keeps the circuit delta Ts at 15 deg F or less should be fine. Using a counter flow serpentine pattern can also help too. No need to run continuous.