Boiler return temp.

Yves

What should to min. temp. be on a boiler return loop?
I have a gas fired slantfin cast iron boiler to heat just a radiant system with a four way tempering valve. It seems if I adjust radiant loop to heat up faster the boiler works o.t. to keep pace, if I turn down the valve it takes longer to warm the house. Thanks.

Wayco Wayne_2

For cast iron

140 degrees is a safe minimum. Radiant floors take a long time to fill. That's why you don't start and stop them like a forced air furnace. You just get it filled with heat and them maintain. WW

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hr

Consider

adding a motor operator to the mix valve to monitor and protect the boiler via return temperature.

It could also add outdoor reset to your package.

A manually adjusted mix valve is not always adequate to offer boiler return protection. A cold high mass radiant can easily overpower a properly sized boiler.

hot rod

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Yves

I live in upstate New York where winters can be brutal, if I use anti-freeze in my system will I lose some of the heat transfer as opposed to just straight water?

Yves

What would recomend? I'm using a Viessmann 1" Mixing valve part# 7133015. Thanks.

zeke

Yes.
For a 50/50 mixture the specific heat will be .8 vs water at 1.The coefficient of heat transfer between pipe and fluid would also go down about 20% but would be less significant.
You probably could overcome these loses by increasing the velocity of the liquid.

Unknown

sLANT fIN

Unknown

Slant/Fin publishes 130° as a minimum return temp.

Noel