Hydronics: 400ft 1/2" pex 1-loop for radiant?

Has anyone ever used a fella that designs radiant systems using 400 to 500 ft lengths of 1/2" pex in a single loop? 500 is his max.

Got a 5,600sq ft slab install and he's saying I can push 11 loops with one Taco 0011 pump and eleven loops at 12" on-center.... all loops 450 to 490ft.

Using closed cell spray foam insulation; so, it should be tight and high R.

Called Taco and from talking to them, the math actually works for the pump, lengths and number of loops (all eleven on that pump). Of course they give me the full lawyer disclaimer and that they are not designers. I can't recall if that was for a 80,000 BTU loss/design or a 150,000 BTU loss/design.

20*F delta. Can't recall, but think 0 or 10*F outside and 70*F inside. Tight house w/high R and U values.

I'm looking for feedback on the fella and the design he pushes. Was hoping to pour by the end of next week!

FWIW, I'm going w/closed loop. Talk boiler stuff later.. just interested in the odd/unique design.

Any comments on this guy, his design and/or reputation? Looking for anyone that has dealt with him or his designs.

Thanks in advance!
S+W

It has been too long since I designed hydronic loops, and then they were copper tubing. 1/2" PEX is really between 3/8" and 7/16" copper, and given the ideosyncrasies of math, a small reduction in diameter causes a large decrease is area, and volume. This being the case, it makes little difference what, or how large, a pump you use, because the length and small size will automatically cause the flow to drop to the point on the curve where the pump output and flow resistance are in balance. Below that point the resistance will be too low and flow will increase, and above that point, if you could do it, the resistance would rise and cause the flow to drop back to the above referenced point.

Depending on what you are embedding the pex in and whether you're using transfer plates, 12" OC may be too far apart for nice even temperatures. FWIW, the guy who designed mine didn't want loops much more than 200' each.

Yea, 230 max really. 5/8 will get you another 70 to 80' but just

It's a fine balance with how long the loop is, the starting water temp, the transfer over its length such that the end is still getting some heat without starting with water higher than you really want. It's easier to use shorter loops to keep the temp similar along its length for nice, even heat. You can't increase the flow rate much to try to improve things or you'll end up with other problems - cavitation, noises, erosion.

long loops play havoc with the delta T and cause mixing issues

I like 300' loops and one big pump.

Big pumps cost big money and more money to run and regardless of those issues there is no point in running 300' runs. It saves nothing and causes huge balancing and mixing issues.

The good pex is typically sold in 300' runs, and why would balancing be an issue with valves on each anyway?

A high head grunfos pump is only about 80$ more than the typical, where you may need 5 or 8 low head pumps. A spare cartridge for the high head pump is about 90 bucks for backup.

I go to 400 and more feet for low need areas. I dont mix and balancing is maybe a 1/4 turn of one valve a year once set up - because I only do OPEN systems, which is the only design that makes any sense. The radiant guys hate them because there are no call backs and racks of needless valves and switches.

Pex is easily available in 1,000' rolls, and with long loops, the water temp at the far end can be quite low, the high flow rate may exceed the safe velocity for the pipe, and you'd have to start out with higher water temps which would lead to uneven heating. A closed system, once properly set up does not need much of any maintenance...it just runs. Multiple loops can often be run with one pump and zone valves, if individual zones are required, or a simple manifold with balancing valves. If you make each run the same length, you may not need balancing valves.

without valves, you cannot shut off a zone or reduce the temp. a 1000' zone might be good in san diego only. Flow would not be a problem, because you would only get a dribble out the end.

ballvalve said:

without valves, you cannot shut off a zone or reduce the temp. a 1000' zone might be good in san diego only. Flow would not be a problem, because you would only get a dribble out the end.

Click to expand...

Nowhere did I suggest a 1000' loop! But, instead of taking a 300' roll and using it as one loop, take the 1000' roll and cut it as needed. If you want good performance, limit a single loop length to 200' or so.