Water temp for radiant over concrete bed

drosner

Hi - I have an upstairs bath that my heating/plumbing contractor is about to lay 1/2 pex that will get concrete with tile on top. He is using the existing supply line that come off the boiler. As an interested "hydronic nerd" I always thought you had to mix the return to lower the water temp for radiant.

When I asked him how he was going to do that he looked at me as if I had 3 heads. He said you don't lower the water temp and that the flow rate, pex material, area of the loops are what contribute to the floor and room temp. The new radiant floor will be on a zone with a baseboard and 3 other radiators - so I'm happy if we don't need to figure out how to get the water cooler for the floor. But everything I've ever read said that you need to lower the water temp for radiant. Also my other radiant floor from the eighties in a first floor slab looks like it gets mixed with return water at the boiler.

So does this guy not know what he is doing?

Brewbeer

It sounds like the bathroom floor should be controlled separately.

drosner

That's what I thought but I'm maxed at the control unit with 6 zones and circulators so adding another zone and the piping would kill my budget.

Is it wrong to use the same water temp for the radiators - 120-180 (at max) for light concrete over a wood subfloor?

Gordy

You need to mix. Is this the only source of heat for the bath?
How many SF of radiant?

Gordy

At 180 you will never have to worry about a wet floor.

Brewbeer

drosner said:

That's what I thought but I'm maxed at the control unit with 6 zones and circulators so adding another zone and the piping would kill my budget.

Is it wrong to use the same water temp for the radiators - 120-180 (at max) for light concrete over a wood subfloor?

Forget the budget, running 120-180 water temps in a thin slab under tile will kill your feet.

Mark Eatherton

I'm thinking he may be a hydronic/radiant wannabe. No one with any amount of experience would attempt such a feat. A hard surfaced highly conductive floor might require 125 degree F water at design conditions. There are some means of utilizing high temperature water, but tube laid directly in an over pour are not it.

Ask him to show you the calculations of design, and what temperature the floor will be at during design load conditions.

What means does he intend to use to induce flow through these small bore pipes?

Usually, it requires a separate pump and mixing station to correctly address the low temperature needs, and even with that , in an existing situation, it is really difficult to make it work when YOU want it to work, instead of when the thermostat the zone is connected to decide for it to work.

Normally recommend a completely separate low temp branch from the mechanical room to the load served.

ME

Rich_49

Use the find a contractor feature and find someone who knows a little bit about heating because your guy is not that guy .

drosner

Very helpful comments folks....one last question - if I wanted to try to keep the radiant room on the same zone as the radiators...is there a mixing value/apparatus that uses the return line of the radiant floor - or do you have to mix with return line back at the boiler?

Rich McGrath - Do you service Bucks County PA 10 mins past New Hope by chance?

Rich_49

Contact me by private message or phone using my information .