I just got my radiant floor up and running and I have a question on room temperature controls. I noticed that if the ceiling lights are turned on, they produce enough heat to warm the air in the room and the radiant does not turn on. Right now I have just a standard on/off themostat. What would be the best way to control these two variables(heat produced from lights and keeping the floor warm at the same time).

Thanks

wow. you either have a very low load, or a whole lotta lights!

You could change the lights or perhaps add a floor sensor, but if the lights can satisfy your load you'll probably find that you won't have a warm floor.. you can condition it so it's not cold, but it will probably have to stay cool to the touch or you'll overheat the room.

Best of luck.

I actually have both. My loads are quite low and I have about 20 "cans" in the ceiling. These are on different circuits so they all are not on at the same time. I have a manual thermostatic mixing valve to set the water temperature. I'm guessing there is not much I can do unless a change to a automatic mixing valve, one that can change the water temp on the fly based on both floor and air temperature. Would this be correct?

well, a floor sensor would "stutter" the heat but it would help. Naturually indoor feedback would be superior, but personally I would start with a floor sensor and see how it goes first.

What would you recommend as to a thermostat capable of that?

Thanks

if you can run a couple of extra conductors the tekmar 509 does the job (or a 508 w/079 or 072 sensor).

I still have access to the thermosat wiring so I can a pull new cable (i was planning on it anyways). I will investigate the 509.

Thanks for your help.

There was a good discussion about radiant floor heating and very low load spaces a while back on heatinghelp.com. Is there any way to isolate the heating loops in the floor so only the areas where you want a warm floor can be kept warm, and let the other areas be cool? This way the smaller floor radiant emitter surface may run a little warmer for the base heat load, thus providing the warm floor without overheating the space. The other thing to consider is that all North American wall thermostats measure "air" temperature and do NOT measure mean radiant temperature. We're still trying to control radiant systems from improper control devices. The closest one can approximate proper control is with the Tekmar series with the in-floor temperature sensor coupled to the PWM wall thermostat.

you know, I can see the point of the "less coverage" arguement, but for the life of me I cannot get behind artificially raising your operating temps (which is another effect of reducing your emitter size) for that, especially if real comfort is achieved otherwise...

I'd rather eliminate the psychology of the "warm floor" marketing...

But that's just my basic stance. You do what the owner wants, right? heh..

I understand that having a radiant floor doesn't mean you would have a "warm" floor. I was just trying to minimize the extreme of when it totally turns itself off for an extended period of time.

well geoff is pointing out that you CAN have a "warm" floor... as long as you're willing to restrict the amount of space that's heating, that space will have to run warmer to do the job, and so you could, say, have a major pathway "warm" and less travelled areas "cool".

I just am not a fan of that.

Yeah, well maybe it's splitting hairs a bit. In the low load homes it means running the smaller floor areas with loop temps maybe 5F to 8F warmer than if the whole floor was heated. Considering that in the low load homes you would be running maybe as high as 85F-90F water as the HWS temp for a "whole floor system", what's the difference between running 95F HWS vs 87F HWS?

You still get the warm floors where the occupants want it, you still get the heat output for the heat losses, and you could conceivably use less material and a smaller system at the end of the day, if it was designed that way from the start.

Just another opinion, one of many.

Just out of curiosity, does anybody know how many BTU's/hr a typical halogen 60 or 75w lamp would put out?
A typical tungsten filament puts out about 10% light, so the rest would be heat. If we know the watts, lumens and efficiency, how would you calculate btus?

I have this lamp on my desk:

60 watts
800 lumens
90% efficient (90% heat, 10% light)

any takers?

Heat from incandescent lights: as you've pointed out, a 60 watt incandescent bulb will put out about 50+ watts of heat - convective air heat with some radiant heat component. 50 watts = 171 Btuh of heat

Geoff, that's a good point on the restricted floor thing. I need to play with some numbers. What kind of ideal surface temp are you targeting, 76 or so?