System Bypass

Cog

Hi
I am trying to control the return water temperature from a radiant floor loop. I installed a bypass well it doesn't work. It completely bypasses the boiler. Iam using a indoor wood boiler with a hanging hot water unit heater a pump dedicated to that system. The radiant loop has its own pump located on the return side. Attached is a picture of the radiant loop. If I move the pump from the return to the supply will this send excess hot water back to the boiler. I marked the location with an x. Thanks

hvacplumber7

I believe that because you have a mixing valve for the radiant, you need to pipe the system primary/secondary.

Gordy

Technically the circ should pull flow through the mixing valve to begin with anyway to work properly for the radiant.

You should use a 3 or a 4 way mix valve to protect the boiler from low return temps. A bypass does not guarantee high return temps to the boiler.

hot_rod

Here is one way with a primary loop, thermostatic valve for protection, and the mix valve for the radiant.

You may need to add a buffer tank to make that wood boiler behave properly. It's tough to build a fire to the exact load.
Wire the unit heater to run should the boiler reach an over-heat condition also, as a dump load.

Cog

The crazy thing the instructions for the Honeywell mixing valve show the pump on the return side with the option of putting it on the supply side. your correct I should have put in a 4 way mixing valve. I have no bypass on the boiler and it works fine for the hanging unit heater. The floor heats fine just a lot of cold water in the return. So do you think I could get some control if I move the pump?

Gordy

@hot rod drawing with the addition of a thermostatic 3 way guarantees a set return temp to the boiler. This allows you to utilize your present mixing valve.

The way you are presently setup with the bypass valve open the circ is pushing the supply water away from the main return piping back to the boiler. Possibly even mixing return from the radiant with supply before it hits the mix valve.

Cog

After this heating season is over I will make those changes. Thanks to all for some input.

hot_rod

Just a basic 4 way would not assure protection either, unless you add a motor and a temperature control.


Unfortunately boiler installation manuals have shown that bypass pipe and valve for years, it is not a viable solution as you have experienced.


Your fix needs to include some sort of valve or pumping arrangement that can respond to temperature at the boiler and make the necessary corrections.

Solid fueled boilers are very sensitive to low return temperature. Creosote build up happens very quickly with cold operating conditions.

SWEI

Unless you're planning additional controls, a Taco iSeries-R valve is probably the simplest option.

Idronics #10 and Idronics #17 will are more than worth the time it will take to read them.