warm kit floor surrounded by CI rads

Timco

Mod con...Hydrotherm KN series 200K. I was considering just jumping the zone with the warm floor and see if it keeps up, and if not then a ded t-stat that can make a call for heat independantly.

Tim

Timco

Cust needs to pull out a CI rad and put in a warm kit floor to make room. Question is if the house has just one zone, will the warm floor keep up with the kit like the old CI rad did, or should the kit be it's own zone with a t-stat? Very nice old home. Will do heatloss calcs after closing. Will be using a 3-wy mixer and a dedicated circ off the 4-zn controller for this application with wirsbo joist trac & 1/2" tube...You know the drill...

Tim

Mike T., Swampeast MO

I suspect you'll need a dedicated thermostat for the kitchen. The real question becomes, "Do I allow just the kitchen thermostat to make a heat call?"

What kind of boiler? Traditional or mod-con?

Mike T., Swampeast MO

I have a feeling that "keeping up" won't be the problem and that you'll need a thermostat to keep the temp down in the kitchen. Glad you're using "right below the finish floor" radiant as opposed to below the sub-floor!

Here's how I believe you can make it work:

1) Use a dedicated circulator for the underfloor with a thermostat that simply turns off the circulator once setpoint is reached--e.g. it cannot force the boiler to fire.

2) Set your mod-cons' reset curve such that it satisifes the high-temp (radiant kitchen) zone as closely as possible, the goal being to keep the thermostat from reaching its cut-off point as much as possible. I would sincerely put in a simple indicator light near the circulator that lights whenever it's active. May easily a season or two of occasional reset curve tweaking to hit the ideal, so if the homeowners are at all inclined, I'd give them good instruction on how (and when) to adjust the reset curve. They should not even consider daily setback in the kitchen--such should be OK in other zones, but not in the kitchen where you're attempting to find the lowest possible curve to barely satisfy the heating requirement. A higher curve only means less efficiency from the mod-con because even if the kitchen isn't calling, it still has to produce the reset target.

3) Use the mixing valve (preferrably with its own reset curve) to supply the rest of the system. The underfloor circuit should obviously be the first thing served (with closely-spaced tees) in either the primary loop or on the secondary side if using a low-loss header.

fatty

i'm no pro - but i would be sure to see how often the boiler runs. if you have huge CI rads, the boiler can shut down for hours between runs... the floor wouldn't hold or emit much heat... after being quite hot for a short time!

fatty

and to ask a question not on my behalf:

i've seen water heaters tapped for small radiant zones instead of boilers...
i have no experience with this but there you have it. i said it.

Timco

I have done this on a few projects...warm a kit / bath floor with a 6 gal electric water heater. This is for a situation where the heat is for foot comfort, not the main heating source. On my current project there is an existing boiler and that is much more efficient than an elect water heater for just the kitchen...I do like your concern about the floor not having the mass of the rads. That is why the warm floor will be on it's own zone so it can be run or killed at whatever the kitchen temp calls for...independent of the house if that is what is needed.

Tim