How is radiant heat water temperature regulated?

[Junkman]

I am slowly trying to understand radiant heat, and what I can't understand is how the temperature in the Pex lines is regulated. The plumber has said that he will be installing a Sparcomix nonn electric mixing valve 3/4" AM101R. I did some reading on the web, and what I don't understand, is if it is introducing cold water to the system, to drop the temperature coming out of the boiler, what becomes of the extra water? Does it get dumped to waste water outlet? Also, some talk about a 3 way valve, and others say to use a 4 way valve. Which is better? I want the floor water temperature to be no more than 120 degrees, so the wood doesn't get too hot, and start shrinking. He is also installing floor temperature thermostats. Below is a link to the PDF installation instructions.

Mixing Valve:
https://forwardthinking.honeywell.c...ll/mixing_valve_tech_lit_and_installation.pdf

Thermostat:
http://www.uponorpro.com/~/media/ex...01-501s_insthb_3_07.ashx?version=062220160829

What I don't understand is how this mixing valve is going to control the water going out to the floor, since the water in the boiler is 175 degrees. I asked if there was going to be a mixing tank, but he said that the system "as designed" doesn't need a tank of any kind. Where does the cooler water come from to drop the temperature?

 

[Radix2]

You need to think of the mixing valve as a way to add water from either the boiler or the return line from the floor to the supply line going to the floor.

there is no "cold water" being added from the outside, the cold water is the water from the floor - all you are doing is circulating that water round and round and mixing some of the hot water from the boiler in as it cools below your 120 setpoint. However much water you take from the boiler, the same amount of water is taken and sent to the boiler from the floor loop - the total water stays the same.

Another way to look at is is two loops joined by the mixing valve. one circulating at the boiler temp, the other at the floor temp - with the mix causing some of the hot water from the boiler to heat the floor loop.

 

[brewchief]

The cooler water is the water returning from the floor, part of it returns to the floor and part returns to the boiler, you only add enough hot water from the boiler to get the output of the mixing valve to the desired temp.

 

[Radix2]

The difference between a three way and a four way is that the three way can protect one loop from the other ( say protect the floor from hot boiler water) but not the other way (protect the boiler from cold floor water).

A four way can protect both loops from each other - making sure the hot loop stays hot and the cold loop stays cold.

If you are using a non-condensing boiler and need to run it above the safe temp for the floor, ideally you would use a four way.

If you are running a condensing boiler and need to run it above safe floor temps (say for a baseboard loop) you could use a three way since there is no need to protect the boiler... you may also be able to plum the system with zoning so that the boiler can adjust the temp for each zone to keep the floor safe to avoid using a mix valve.

If you are running a condensing boiler and can run it at safe floor temps, you don't need a mixing valve at all.

 

[BadgerBoilerMN]

3 and 4 ways are rarely used in the US. They are becoming obsolete as most electric boilers and all condensing boilers have built-in outdoor reset.

If you are using solid fuel, oil or crude water heaters you may need a mixing valve to protect them from cold returns or fix-the-mix to design conditions, but this is less than optimal. The best strategy for controlling radiant panels is with outdoor reset. Again, standard on all gas-fired condensing boilers and an option for most electrics saving fuel and adding comfort.

 

[Bondo]

Where does the cooler water come from to drop the temperature?

Ayuh,.... As noted above, it's the return water from yer loops,....

My system is old school, oil cast iron boiler, primary loop 180°, secondary loop is mixed down to 140°, 'n the in-floor loops run off manifolds in the 2ndary loop,...

It also just uses plain ole wall t-stats, no problems set to 68°/ 70°,....

 

[BadgerBoilerMN]

140F is too high for all but sub-floor wood systems. Slab systems will normally top out in the 120F range in cold climates with poor construction.

 

[Bondo]

140F is too high for all but sub-floor wood systems. Slab systems will normally top out in the 120F range in cold climates with poor construction.

Ayuh,.... Yer right, my bad,....

Fingers weren't hittin' the numbers I was thinkin',.... sorry,....