Radiant Heat Pump

Mikb1957

I'm trying to come up with the right circulator pump for my set-up. I have a cast iron oil-fired boiler with two zones, upstairs and downstairs baseboard. I eliminated the upstairs baseboard and have put in a five zone radiant heat manifold with zone valves. Four zones upstairs and one for the near future in backyard work shop. Longest zone is 300', all 1/2" pet. I have a Taco 5004 c-3 mixing valve. Trying to figure out the right circulator pump to use...Taco tech support said 0034e, a plumber off top of his head said 0010..any suggestions?

GroundUp

Both of those are way bigger than necessary. But the bigger issue here is piping, now that you're going to low temp. Does the boiler have a primary or bypass loop to assure return temps over 140* and prevent short excessive short cycling? Why does the upper level have 4 zones when it used to only be 1?

Rich_49

Mikb .

Why do you have a DHW mixing valve on a heating system ? The valve you have is meant specifically for a pressure system , not a heating system . look at the chart I am attaching , every PSI represents 2.31 feet of resistance , that's why they recommended the large circulator .

hot_rod

5 loops at .50 gpm each is 2.5 gpm
300’ loop of 1/2 is 3’ of head

Add a foot for any piping and that becomes the pump spec. 2.5- 3 gpm at 4-5’ head

About the smallest circ you can buy should cover that

The circ needs to pump away from the mix port

The valve should work fine at that low flow rate. Lowest setting is 85 degrees

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Taco - 5004-C3 - Install Instructions.pdf

Mikb1957

Rich 49,

I checked with Taco tech support. They say the valve is the same exact one as the radiant heat only valve. Only difference is 5004 c-3 is rated for DHW (lead free). Thx.

Mikb1957

GroundUp,
I went from one zone on upper level to 4 because it had one loop of baseboard. My new set up is four rooms on their own thermostats, piped with 1/2 pex, each run between 200-300 ft.

As far as the piping, I've been researching that, and have found some information and diagrams showing two tees close together with a second mixing valve.. trying to find a diagram with my set-up.. baseboard on main level and the upper level with the radiant heat manifold. I am replacing the upper level CP with one mounted after the mixing valve and before the radiant manifold. Thx.

Rich_49

Mikb . Well that's real nice , however it's still not the correct valve for the job . Look at the chart , figure how many gpm you require then figure out the head loss of the circuits . The Cv on the radiant mixing valve is 2.3 which means 2.3 gpm will impart 1 psi pressure drop through the valve . The radiant heat setpoint I Series has a Cv of 7 . Be careful also because Cv is not linear , it's exponential .

Joe Mattiello

great that you're taking the time to size the circulator for intended duty. Contact taco tech support for help with sizing, and go with what will work without oversizing pump to minimize any velocity issues.
Taco tech support is 401-942-8000

Mikb1957

Rich 49, I get what you're saying now, thanks for the heads up.

hot_rod

5 loops of 1/2" pex, call it 3 gpm total.
Thru a 2.3 Cv thermostatic valve, here is what the pressure drop would be.
Just under 4' of head. Still within a typical small wet rotor circulator.

Rich_49

hot_rod said:

5 loops of 1/2" pex, call it 3 gpm total.
Thru a 2.3 Cv thermostatic valve, here is what the pressure drop would be.
Just under 4' of head. Still within a typical small wet rotor circulator.

With all due respect BOB . Where does the 3 gpm number come from , since when do we take SWAG on someone's question ? He has 5 loops of now and future radiant and a baseboard zone whose requirements we do not know , but venturing a guess since that's apparently what we're doing mine would be a minimum of 1 gpm since that's how baseboard is rated . What if these loops require 1 gpm and then we end up with a 7 gpm need . You will have given this man bad advice . Instead of having to be right maybe just give the advice needed for someone to figure it out and do it themselves . To be clear , it is my belief that your numbers are a fairy tale and may not work for this man , shame on you .

hot_rod

With great curiosity RICH what flow rate do you suggest for 300’ 1/2” pex radiant loops?

I read it as he has removed the fin tube and added radiant loops. I doubt he would need a mix valve on fin tube, 300’ 1/2” loops? Do you run thermostatic mix valves on fin tube?

The OP can clarify if he is running 1/2 radiant or 1/2” to feed fin tube baseboard

For radiant loops The Radiant Rad Pad suggests .6 gpm. Others may suggest .5 gpm
He indicated he had 4 radiant loops with a possible 5th to be added

5 loops X .6 gpm = 3. When I went to school

3 gpm is plenty workable with the 2.3 mix valve he has, as I showed above
Taco seems to agree, as does the manual that comes with the valve. Sounds like you disagree? And suggest a lowlead valve. Instead?

Mikb1957

Guys, I removed the fin tube and ran the 1/2" pex as 4 radiant loops, each on own zone valve, each of the four rooms will have own thermostat. The 5th future will run out to a shop in outside shed, so allowed for 40% glycol in system.

Rich_49

With great curiosity RICH what flow rate do you suggest for 300’ 1/2” pex radiant loops?

I suggest performing a heat loss and using the temp , gpm that are required at various outdoor temps BOB , that's what I suggest .

I read it as he had 2 zones on BB , one up and one down , well here is what he siad , " With great curiosity RICH what flow rate do you suggest for 300’ 1/2” pex radiant loops? " QUOTE .

Systems SHOULD work well and as designed through a large range of ODTs and SWTs , BOB . You know this , and stop using formulas for 60* fluid .

I just looked at a recent design , a loop is 300' exactly , 12 " spacing 150* SWT , 20* Delta , .7 gpm and the head is 3.2 . So if someone required .7 gpm at a 10* Delta what would the head be . Nobody even asked where is this , what is design day conditions . None of it yet you're spouting off advice that may or may not be good . I suggested a valve specifically for heating systems .

hot_rod

So we use your . 7 gpm per loop X 4 or 5 loops, still at 3,5 gpm, well within that mix valve.
And the 0034 Taco suggested🤓

Mikb1957

Thank you all for the discussion

hot_rod

Mikb1957 said:

Thank you all for the discussion

The 40% glycol needs to be factored in the pump selection also.
A quick read on sizing circulators here.

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_16_NA_Circulation in hydronic systems.pdf

Rich is correct, the pump gets sized to the load of the system you connect to. That is the exact answer.

The figures I show are for typical 1/2" radiant loops, 300' with plain water. Your job could require less or more flow (gpm) than that quick calculator shows. As per the RadPad, 1/2" loop at .6 gpm, 12" on center spacing would give you an output around 22 BTU/ sq. ft.

Tighter tube spacing, higher flow rates are ways to get more output. realistically 25 or so btu/ sq ft is about what you get from a comfortable radiant floor. Surface temperature around 82F. Any warmer and the floor becomes uncomfortable to walk on in bare feet.

I was kidding about needing a $1000 circulator

Mikb1957

That's a relief