Question about a floor radiant thermostatic valve

DIYpro

Hi All, I have a hot water radiator system. I want to connect a pex loop under the bathroom floor and there is a pex supply and return running right by it. I want to tap SOME of that heat thru the bathroom floor loop but when the outlet temp reaches about 110f, I want the valve to close and no more bypass thru there.

I can add a tee so the straight path is into the bath loop and it will flow, but the outlet downstream should have a thermostat valve that closes at 110f.

This way the bathroom gets a touch of heat under the floor which will make a world of difference, but never too much.

Just dont know what kind of valve or even what it is actually called and google didnt solve it for me.

Thank You!

DIYpro

hot_rod

what would tell the valve to close at 110? A thermostat, or do you want a thermostatic mixing valve?

DIYpro

hot_rod said:

what would tell the valve to close at 110? A thermostat, or do you want a thermostatic mixing valve?

Hi, I would think there would be a valve that has a built in temperature capability? bimetal or something? I dont really know what to use but the bypass loop needs to close when its outlet sees around 110 so the floor doesnt get too warm...

DIYpro

I wonder if this would work if I cap off the cold inlet. When the water coming into the hot inlet reaches set temp, the valve will close that inlet off???

https://www.supplyhouse.com/Webstone-75102W-1-2-Sweat-Thermostatic-Mixing-Valve-Lead-Free?gclid=Cj0KCQiAlMCOBhCZARIsANLid6asv0otxHwvoRujU7SMJk3FmwE5TnFR3hih9r8uUzmC4YXWKOfhersaAqg9EALw_wcB

hot_rod

Too much pressure drop thru those valves 

you could build a “wild” loop basically two tees with a globe valve between, just flow a trickle to the radiant.

DIYpro

hot_rod said:

Too much pressure drop thru those valves 

you could build a “wild” loop basically two tees with a globe valve between, just flow a trickle to the radiant.

u know I was thinking that originally, but if I could get a thermostatic valve to work, then when the system calls for heat, the floor will warm at the maximum rate and then stop at the valve set point. with a trickle, it would be unlikely to pour too much heat in as it will be dissipating, but my system tends to short cycle die to only 3 radiators, and the bathroom may not really get all the benefit. But it would be simpler!

you introduce another possible issue of the valve holding back flow in the bath loop (it would not restrict the main loop) and then it may not flow enough anyway.

I guess now to find out how these mixing valves work and if and how they add back pressure.

at the end of the day, your idea may be the way to go...

EBEBRATT-Ed

@DIYpro

Do you have radiant heat in the floor on that loop? because you said

"Hi All, I have a hot water radiator system."

and what is the heat emitter in the bathroom? Radiant floor, panel rad or baseboard from below so you could locate a valve there.

Do you have access under the bathroom floor?

hot_rod

It’s just the nature of thermostatic valves either two port TRV, or three port mix valves. If it were that simple….

Google this article for a few options, most require an additional pump.

if you have a high temperature system, and you have access below, Ultra Fin on a wild loop as I mentioned is a good option, no mixing or temperature valve required it just warm the joist bay 

DIYpro

hot_rod said:

It’s just the nature of thermostatic valves either two port TRV, or three port mix valves. If it were that simple….

Google this article for a few options, most require an additional pump.

if you have a high temperature system, and you have access below, Ultra Fin on a wild loop as I mentioned is a good option, no mixing or temperature valve required it just warm the joist bay 

My house has 3 iron radiators, none are in the bathroom.
There is an unused pex loop under the small bathroom floor, not hooked up.

My diagram shows the proposed way to bleed some of the radiator water from one of the radiators through that loop but I dont want it to exceed 110f

If you look above at my diagram, I need a valve that slows and stops that floor loop's water when the outlet reaches 110f.

Since it is parallel, the radiator will always have its water.

EternalNoob

Seems to me too many unknowns to predict the performance you would get through the the bath loop if it's tee'd from the radiant supply back to the supply, as it is in the drawing. You might not get much of any flow through the bath loop regardless of how it was controlled, just by virtue of the water taking the path of least resistance.

If you have access to both the supply and return radiant pipes next to the bathroom, why not just install a mixing valve (<$100 part) between the supply and return. Seems like a fool-proof way to go. Maybe i'm missing something here.

EternalNoob

I guess if your system runs hot, the radiator return may exceed 110F, which could be a problem. I think a good mixing valve should more or less shut down flow if the cold inlet rises above the set temperature, but hotrod knows a lot more about the nuances of mixing valves than i do.

DIYpro

yup those are the issues. just doing this for fun. I will have a ball valve on that little floor loop anyway so if it gets too warm I can just shut that and reevaluate.

the radiator is actually a wild loop itself, 1/2" pex tee'ed from the 3/4" loop to the other two radiators. it has flowed and worked really well for many years. but that has to stay free flowing. I cant switch it to series with the 3/4" loop to maintain pressure because then that 1/2" would slow everything else down and what would be the point of the big 3/4" on the main loop. and slowing the system might cause the heat to overrun the thermostat or something. right now, it all maintains really well within about a degree when left alone (although it does overshoot a little when moving the heat up by several degrees) and rooms are well balanced (bedroom slightly cooler which is perfect).

that said, maybe I will take the advice to just add this as a parallel loop with a manual valve and try that at different settings

I guess its either that or a mixing valve which may slow down the bedroom radiator and make that room colder....

Initially I thought that making it a wild loop with a thermostatic valve at the outlet end which would not slow down the radiator flow because thats parallel.

just for the heck of it can someone point me to a thermostatic valve (not mixing valve) or do those not exist?

Paul Pollets

Oventrop makes such a device that uses radiator temps and mixes for a RFH zone. Directions need to be followed explicitly and it may be out of the realm of a DIY. I've installed over a dozen and they work well for these situations.
https://www.oventrop.com/en-US/productssystems/catalogue/room-climate/surface-heating-and-cooling/surface-temperature-regulation-with-return-temperature-limitation/unibox-room-temperature-control-and-return-temperature-control/240

EternalNoob

I'm not sure this is optimal or if there's something i'm missing, but Just to be clear, I was suggesting tee-ing in the mixing valve (parallel) and therefore not obstructing the existing piping. I.e., taking C inlet from radiator return tee, H inlet from radiator supply tee, and mix through bath RHF to tee back into into radiant return.

DIYpro

EternalNoob said:

I'm not sure this is optimal or if there's something i'm missing, but Just to be clear, I was suggesting tee-ing in the mixing valve (parallel) and therefore not obstructing the existing piping. I.e., taking C inlet from radiator return tee, H inlet from radiator supply tee, and mix through bath RHF to tee back into into radiant return.

ahhh that clarifies it thanks! I think it was hotrod who mentions those impede flow though and since this is a bypass loop it wont work with any resistance.

now the key is to find out how if a mixing valve holds back flow at all.

paul polletts product suggestion may apply too

thanks to everyone so far

EternalNoob

Ok, i see what you're saying by pressure drop. If the resistance of the mixing valve plus bath floor loop exceeds the resistance of the radiator, you get no circulation in the floor. Or to say the same thing in different words if the pressure drop across the radiator is not enough pressure to drive your valve plus loop, you get nothing.

DIYpro

EternalNoob said:

Ok, i see what you're saying by pressure drop. If the resistance of the mixing valve plus bath floor loop exceeds the resistance of the radiator, you get no circulation in the floor. Or to say the same thing in different words if the pressure drop across the radiator is not enough pressure to drive your valve plus loop, you get nothing.

yup and dont forget that the whole (1/2") bedroom loop is parallel "wild loop" off the 3/4" main loop. otherwise I could restrict the radiator a bit and balance it that way. but not an option now.

prob just tee it in and put a valve at one end and see. like I said, anything is better than nothing. be nice to have the bath floor warmer and dry fast after a shower