Radiant question

JIMBO_2

I have an older house (1930s) with hot water heat (TT-110) and CI rads.  Our kitchen was remodled 30 years ago, the old radiator was removed due to new counters and CI baseboard was added in the only remaining place--on the wall oposite the exterior window.  The old radiator did not really heat the room very well either, but the old boiler was directly beneath the kitchen and it gave off pleanty of heat which helped heat the kitchen above. The kitchen does not get warm enough, I suspect due to lack of BTUs and it's location.  I would like to install radiant under the floor, which is completely open in the basement below.

In the basement the boiler feeds 2 inch black pipe from supply and return.  Is it possible to tee off the 2 inch pipe to feed a radiant system?  ANd if so, what sort of radiant might work best?  Hard wood floor in a room that is about 8 x 10 feet.  Any ideas? 

L'town Radiant_2

Probably...

The addition of radiant is likely not an issue, so long as you boiler has extra capacity to add a heating zone to it. running two runs of tubing on 8in centers through each joist bay in aluminum transfer plates is probably best. it would be critical to insulate the joist bays under the tubing. Currently your boiler probably sends 180deg water out to the radiators, this is too hot for a sub-floor radiant application. You would probably need in the area of 125-150deg supply water. There would need to be an addition of several new control components: t-stat, mixing valve or injection mixing set-up, pump/valve relays.

Yes it probably can be done, and probably without too much trouble, but it definitely needs the insight of professional who will do it right the first time. An improperly designed system could lead to damaged floors, damaged boiler, or at the least a system that doesn't work.

Alan (California Radiant) Forbes

Radiant loop

I would normally install plates as well, but since this is such a small area it will be a lot easier to run the tubing in the joist bays without plates at the same temperature as the radiators - around 180°; insulate under the tubing and leave an air space  to allow for convection.  You can tie it in to the existing living space zone if the other rooms have hardwood or make it a separate zone.

L'town Radiant_2

Good thinking...

Yep, that's good thinking Alan. I wouldn't have normally considered that, but it certainly sounds like a good option. I may well be wrong here, but I would still be worried about high floor temperatures if the zone is not independently operated. Then again, I guess if the floor loop comes off the return of a higher temperature zone, you might be dealing with about 160deg....well, just thinking out loud here...good suggestions though.

Alan (California Radiant) Forbes

The question is

will the room with radiant heat warm at the same rate as the rooms with radiators.  Like you said, the correct answer is to make it a separate zone.

JIMBO_2

What if?

How about?  Remember, I am not a radiant guy, but what if I put a TRV on the radiant "zone" tubing under the kitchen floor, with the sensor bulb in the kitchen, of course?

Alan (California Radiant) Forbes

That would be

the same thing as a thermostat.  I'd go with a thermostat since an 18-gauge thermostat wire is easier to install than a capillary tube.

JIMBO_2

Thanks

If the TRV will work, It is easy enough for me to go that route, and I have a few TRVs sitting on the shelf.  But what sort of radiant would be my best option?  The floor is 4 x 1 inch T&G hard wood and the basement beams are wide open. 

Gordan

About TRVs and radiant floors...

A pro I've been talking to about my own project pointed out one thing about using TRVs: they basically modulate output by widening delta-T which, with the supply temp remaining constant, lowers the average temperature of the emitter. (And they do this by actually restricting flow.)



That would mean that your floor temperature would vary quite a bit along the loop. Siegenthaler's book on radiant heating suggests that the delta-T in a floor loop should be 10 degrees F, max - for what it's worth. Oventrop schematics for the loop layout for their Uniboxes get around this by specifying a different tubing layout, but this would seem to be impractical for between-the-joists piping.



You could also get around this if you used the TRV in a mixing circuit to vary the supply temp instead of flow.