temper heat supply on radiant heat

**Peter Louis** · 03-20-2014, 10:29 AM

I always look for the temper valve when inspect the radiant heat system. But not very often I can find it as pic2. Most scenarios are like pic1. Is the thermostate doing the temper valve job instead? Also I have never seen the temper valve on any indirect heated HW tank.

Thank you

**John Kogel** · 03-20-2014, 02:35 PM

Peter, could you write your question in French so we can understand it better?

A newer system will have the newer technology and the newer plumbing hardware. An old system may not or it may not be comparable. I think the operating temp of the boiler would have a lot to do with whether a tempering valve is needed.

**Peter Louis** · 03-20-2014, 03:50 PM

Originally Posted by John Kogel

Peter, could you write your question in French so we can understand it better?

A newer system will have the newer technology and the newer plumbing hardware. An old system may not or it may not be comparable. I think the operating temp of the boiler would have a lot to do with whether a tempering valve is needed.

Thank you John, but all the radiant boiler operating Temps I have found are about 140-170F. I can only see a return pipe back to hot supply. Most chances this pipe has a partially opened shut-off valve before reaching the hot supply pipe.

**John Kogel** · 03-20-2014, 08:14 PM

Peter, there may be a check valve which allows water into the boiler system but prevents water from the boiler from returning to the fresh water supply. That would be called a 'makeup' valve.

Excess water in the boiler loop can only blast out of the pressure release valve.

Maybe you are talking about something else.

**Jim Robinson** · 03-21-2014, 07:09 AM

I'll take a shot at it. I run into this a lot, or at least I think this is what you are referring to. Typical setup: The house has a standard issue boiler connected to in floor radiant heat. Yes, there should be a tempering valve on the boiler that will allow the boiler to operate at 160-180, yet deliver water to the in floor at 120-130. Most houses do not have this, and they try to work around it by either lowering the internal temperature of the boiler or by sending hotter water to the in floor than it should have.

I've looked up the instructions for the majority of the boilers that I see on a regular basis, and they all call for the tempering valve, often referred to as a mixing valve, if return temperatures will be below 130 degrees F.

There are certain high efficiency boilers that are designed to run at lower temperatures. These do not require a tempering valve. The Raypak is another unit that doesn't seem to require one, as they have a built in bypass, and according to their manual can be run down to 110 deg F on the return side. The high efficiency boilers are normally a condensing type, and you will see the condensate drain system, as well as the Cat IV vent type.

**Peter Louis** · 03-21-2014, 06:19 PM

Originally Posted by Jim Robinson

I'll take a shot at it. I run into this a lot, or at least I think this is what you are referring to. Typical setup: The house has a standard issue boiler connected to in floor radiant heat. Yes, there should be a tempering valve on the boiler that will allow the boiler to operate at 160-180, yet deliver water to the in floor at 120-130. Most houses do not have this, and they try to work around it by either lowering the internal temperature of the boiler or by sending hotter water to the in floor than it should have.

I've looked up the instructions for the majority of the boilers that I see on a regular basis, and they all call for the tempering valve, often referred to as a mixing valve, if return temperatures will be below 130 degrees F.

There are certain high efficiency boilers that are designed to run at lower temperatures. These do not require a tempering valve. The Raypak is another unit that doesn't seem to require one, as they have a built in bypass, and according to their manual can be run down to 110 deg F on the return side. The high efficiency boilers are normally a condensing type, and you will see the condensate drain system, as well as the Cat IV vent type.

Yes, exactly.

**Rod Butler** · 03-26-2014, 03:26 PM

Originally Posted by Jim Robinson

I'll take a shot at it. I run into this a lot, or at least I think this is what you are referring to. Typical setup: The house has a standard issue boiler connected to in floor radiant heat. Yes, there should be a tempering valve on the boiler that will allow the boiler to operate at 160-180, yet deliver water to the in floor at 120-130. Most houses do not have this, and they try to work around it by either lowering the internal temperature of the boiler or by sending hotter water to the in floor than it should have.

I've looked up the instructions for the majority of the boilers that I see on a regular basis, and they all call for the tempering valve, often referred to as a mixing valve, if return temperatures will be below 130 degrees F.

There are certain high efficiency boilers that are designed to run at lower temperatures. These do not require a tempering valve. The Raypak is another unit that doesn't seem to require one, as they have a built in bypass, and according to their manual can be run down to 110 deg F on the return side. The high efficiency boilers are normally a condensing type, and you will see the condensate drain system, as well as the Cat IV vent type.

I agree. The only bit I'd like to add is that the in-floor radiant heat should never exceed 105 degrees.

**Jim Robinson** · 03-26-2014, 04:20 PM

Originally Posted by Rod Butler

I agree. The only bit I'd like to add is that the in-floor radiant heat should never exceed 105 degrees.

That's a pretty low number. I use 120 - 125. But, it will depend greatly on where that number is measured, and the type of system. At the return that would probably be about the same as a 120 output temperature. There is a lot of staple up here, which needs a higher delivery temperature than tubing in the slab would need.

**Rod Butler** · 04-07-2014, 02:00 PM

Originally Posted by Jim Robinson

That's a pretty low number. I use 120 - 125. But, it will depend greatly on where that number is measured, and the type of system. At the return that would probably be about the same as a 120 output temperature. There is a lot of staple up here, which needs a higher delivery temperature than tubing in the slab would need.

I agree Jim that staple up should run at a higher temp, that's why I said "in-floor" radiant.