Cast iron radiator on same zone with Radiant

Dan C.

I have a small radiant zone in a slab. It is about 6000 BTU. Right next to this room with the Radiant is a laundry room.
They want me to put a leftover cast iron radiator that was removed from the main house in this laundry room to heat it off of the same zone is the radiant. I have never done anything like this but I think it would be possible. I want to either run the primary loop through the radiator before it goes to the mixing station or run a homerun from the primary pump through the radiator and then also use that same pump for the primary loop of the radiant. Can this work?

Jamie Hall

If you run it through the radiator first, then the mixing valve, you will have a decent chance of getting hot enough water in the radiator to work. Your basic problem is that the radiator is expecting water at 140 plus, and the radiant loop should be nowhere near that.

Dan C.

I have attached a very quick drawing. I would prefer to do it this way over running it through the radiator first. So that the radiator can have a TRV on it if necessary. Would this work? Radiator is 25 EDR. Radiant is 6000 BTU.

Dan C.

forgot to attach the picture

Dan C.

Photo

hot_rod

What temperature is the boiler or primary loop running? The hottest SWT will be the first takeoff from the primary loop.

I don't see where the boiler is in that piping, looks like another zone pump would get you the boiler temperature for the radiator,then it is able to run regardless of the radiant loop running.

Dan C.

I added the boiler in this picture. The boiler loop and primary loop is set to run 120-180 depending on OD temp. I don't want to add a zone just for this one radiator. The radiator heating only when the radiant zone is on is not an issue and was discussed with the homeowner. He just wants some heat in the room. It can be colder than the radiant zone.

Jamie Hall

That location for the radiator should work. It's temperature will be independent of the radiant loop temperature.

hot_rod

Dan C. said:

I added the boiler in this picture. The boiler loop and primary loop is set to run 120-180 depending on OD temp. I don't want to add a zone just for this one radiator. The radiator heating only when the radiant zone is on is not an issue and was discussed with the homeowner. He just wants some heat in the room. It can be colder than the radiant zone.

One suggestion would be to add a balancing valve to assure the radiator gets enough flow, the primary loop looks to be the path of least resistance, so actual flow to the radiator would be a question.