Reducing radiant floor temp

drosner

I’ve got a well insulated small bath with a radiant zone with the return feeding the mixing valve to control temperature. The feed line from the boiler is 180. Thing is the floor isn’t loosing enough thermal energy so the return water temp is usually around 120-150. The wax ring on the toilet melted and we had a pretty expensive repair that I’d like to avoid again.

Is this common and do I just use a return from any other zone or is there other options I can do here?

neilc

show your mix valve, and how the circ to the floor is piped,
how old is the mix valve?

drosner

Mixing valve is about 8 years old. Here’s the picture where you can see boiler supply and return going to mix valve then to the circ before heading to the floor. I guess I’m wondering how the mixing value can lower the water temp below the return temp?

hot_rod

I doubt you need much more that 80-85 degree supply to a tile floor, what are you sending out? If you set a mix valve for 80 degrees it should not vary more than a few degrees. So how does the return get warmer than the supply?

What controls the heat in the room? A wall thermostat? A floor sensor?

You can get rubber or foam toilet seals now, a much better option for radiant floor heat

drosner

I’ve got a basic wall t-stat…

Maybe I don’t know how the mix valve works. Doesn’t it take the return flow and mix it with the supply to lower the temp? So if the return is always above 120 or so I’ll never get the floor to lower than that right?

Hot_water_fan

@drosner it mixes hot with low to get medium. So if you supplied 180 and only need an average of 100, it would only let a trickle of 180 through, mix it with the return temp of 95, to get 105. So it sounds like your mixing valve might be letting too much hot water in. 

hot_rod

Most mix valves go down to 85° supply, once that temperature water goes around the loop it will come back 10- 15° cooler. So it is the 70 return water blending with the 85 water. There should be no water in the loop above 85?

If the valve is piped and working correctly.

It should be piped like this. Hot supply into the H port, the C port gets the return from the loop and goes back to the boiler also. The pump pulls from the M or mix port.

neilc

the floor return should be piped to the cold side of the mix valve, and also to the return to the boiler, between the cold side of mix, and return to boiler, you should have a check so nothing flows back from boiler return to mix cold side,
boiler supply should pipe to hot side of mix valve,
looks like you are pulling from the mix of the mix valve, that is correct,
the return from the floor, and a small amout of boler suply, should circ out to the floor,
what little hot you pull from the boiler, would return to the boiler on the cold side return, thru that check,
do you have the check valve between the cold side of the mix valve, and the return to the boiler?

neilc

if the floor supply is too hot, and you have the check, maybe the mixer is seized or sticking,

drosner

Yea I think in my case my son cranks the heat because he likes the floors always warm. So lots of times when it’s calling for heat the floor is already plenty warm and therefore the return it’s way too high. Appreciate the insights. Will run some tests but I think I simply have a bad mix valve and need to keep the room temp below 80…

neilc

the room thermostat has no control over the mix valve, the mixed supply temp, or the floor return temp,

do you have the check valve on the return to the boiler return?

mark the adjuster knob, now turn it clockwise, and counterclockwise, repeatedly,
see if you can get a full turn, or more, or just go to resistance,
back and forth, forth and back,

now adjust it to a bit cooler than you had it,
what's that supply temp?
and after running the room circ for a while, is that supply temp still rising?

do you have the check valve on the return to the boiler return?

drosner

No check valve on return side of this zone. What problem does that cause?

Got it on room tstat but my son just cranks it to max (it’s a dial analog) because he thinks that is “max” for floor. Then he goes to school and thinks nothing of it. By the time the room gets to 90 or so the floor is cooking and the return no longer can bring down the supply.

But if I figure if I set the med properly it’ll never get hot enough to get to that point. Right now I can turn it clockwise forever and it doesn’t stop. So I figure I got a bad mix valve.

Hot_water_fan

You’re misunderstanding what’s happening, but the answer is still the same: have someone check if the mixing valve is working. 

neilc

ya know, I think I have confused myself with domestic mixed valves, where the "mix" can be disposed of, down the drain, and could pull from a hotter or colder source
this being a closed loop, I can't see that the check matters,

and I'm pretty sure you can't make the water hotter just by overheating the room, even if the room was at 90,
how much heat would transfer back down to the floor and radiant loops?

yeah, set that mix down, so the room thermostat barely matters, hard part being the changing outdoor temp and variable heat loss, consider a mix valve with outdoor reset,

about the knob spinning to no end,
it's stripped(?),
take the knob off and pliers on the stem, don't mar the stem next to the packing,
rebuild the valve,

hot_rod

Does that circulator have a check in it? that should be enough resistance to prevent ghost heating.

If that mix valve is an ASSE 1070, those come with checks in H & C by the listing requirement.

If the mix valve is set to 85, I doubt you will over-heat the room, except on very mild days where it is cranked on all day.

Maybe you need a spring wound timer to control the floor, in conjunction with the t-stat if it is being "over-used
Or a meter that takes quarters like a carwash