Very small radiant loop

Jim P

I have a customer that wants to intsall radiant floor heat in her 5x7 finsihed bathroom. I am planning on using Wirsbo joist track under the floor with 1 circut (1/2 he pex). Are there any do's and don'ts with such a small radiant system. I was planning on using a thermostat in the bathroom making it a new zone. The rest of the house has baseboard heat with a WM ultra boiler.

Thanks,

JWP

Norm Harvey

Whats the heat loss for the room and the available square footage for tubing. If you cant get under 35 BTU/ sq foot then you wont be able to heat the room adequatley alone. You may want use quik-trak instead and also put some in the shower stall floor and walls. Or you can go with radiant for "floor warming" and install supplimental heat to keep up with the loss.

So what are the numbers?

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Jim P

Thanks

Thanks Norm,

I will get those numbers tomorrow.

JWP

jp_2

go electric

my gosh, 5x7 on a what. maybe 70,000 btu boiler???????

Jim P

Norm

Norm,

The available square footage (clear floor space) for heat is 18 ft2. I could put some heat under the tub, but that probably will not warm the room too much. The bathroom is already finished so this would be a below the floor application. Presently there is no heat in this room at all. The btu loss for the room is aprox. 1262. After reading your last post I see why you mention floor warming. If the customer wants floor warming, what is the best way to control this? A thermostat probably wouldn't satisfy.

Thanks,

Jim

Norm Harvey

I'd use one of those recessed fan coils between the wall studs for your main heat, then run your radiant through a thermostaic valve to run whenever the zone circulator runs.

When the room is satisfied the radiant will stop. Thats the cheap way. Disadvantages is that that thermal mass of the floor may take a bit to heat up, so you wont have a consistent floor temp.

If you wanted to maintain a constant floor temp, you could use a thermostat with a floor sensor just for the radiant floor, and pipe them independently.
I would mount the thermostat for the radiant on the joists where the tubing is (it doesnt need to be int he bathroom) Set the room sensor to "off" set the floor sensor to "on" and set a minimum and maximum slab temperature and use that to control the radiant circulator.
Depending on what your boiler is (if theres a tankless or some other minimum temperature you need not have the floor sensor thermostat even call the burner.
If its a cold start Boiler... we can thinkof some other control schemes.

Im not sure of I explained things right.

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hot_rod

sounds like a big load

for 35 sq feet of room. 3 outside walls? Window? no insulation?
How is the room heated now? It must get some heat from the rest of the home.

Your heat flux (available square footage to load) is working against you if the load is that large. You would need uncomfortably warm floors to get close to that load.

Still, some plates from below 6" on center with a floor sensor would certainly help the space. Warm floors in a cool space are much better than cold floors in a cold room

Any way to get some heat in the walls? Warm bathroom walls, especially tile, really work great.

Consider a Laing EHT combo heater/ pump. It's a great way to heat a small space and can be run year ' round without firing a boiler.

Or even a 6 gallon electric HW tank with a pump and expansion tank. With a 6 gallon you can install the exact wattage element to cover the load.

hr

Norm Harvey

Hot Rod, that Laing is a sexy thing! I'll have to look more into that!


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optotapiccaws2257205

The customer

does not want any additional heat in the bathroom except for what the radiant will provide. Control wise I was planning on using the Wirsbo 501s with the floor sensor.

Thanks,

Jim

jp_2

your data shows

if I am mistaken, 1262 btu's over 18 ft ^2, 70 btu's per square foot? have you done that before? what do you figure the floor temp would be? you can't give the customer what can't be done.

listen to hot rod's advice.

optotapiccaws2257205

I see your point

and I have spoken to the customer about this and they still want to go forward with this small radiant zone. Hot rod made a good point by stating that "Warm floors in a cool space are much better than cold floors in a cold room :" I guess my next question is what is the best way to control it? Now I understand the terms and differences of radiant heating and floor warming.

Thanks,

Jim

PDM

I used warmboard in both my recently rennovated 2nd floor baths. The heat goes under the tub in one bath, and under the walk-in double shower in the other. I was able to reduce heat loss by furring the outside block/brick walls, adding foam insulation, and also adding weatherstripping to the double hung windows (go to www.conservationtechnology.com). I used Tekmar 509? with a slab sensor. The comfort is incredible, especially in the shower. If I had to do it again, I'd put heat in the shower bench and walls as well and give the shower its own loop (that would be real luxury).

Because these loops are pretty low in BTU's, the tankless boiler cycles a bit more than I'd like. I'm considering adding a highly insulated storage tank to the system but need to noodle that for a bit.

Remember too that for most baths, people will leave the hall or bedroom door open to the bath except when they are in use, so these rooms can 'borrow' some heat from adjoining spaces. Also, when in use the ventilation is running, drawing in air form adjoining spaces as well.

Note that for the Texmar, I have it set to control room temp (at 68 degrees) but I put the slab min temp at 75 and max and 85. 75 is the magic number for a tile floor that doesn't feel cold.

Be sure the hot water enters the zone along the outside wall.

Pat

Phil_17

Scary how similar this is to what I just finished...

Let's see:
Renovation, two 2nd floor bathrooms, Warmboard, Loop runs under bath and shower, Tekmar 509 with floor sensor (I used the 510), Foam (icynene) in the exterior wall, New low-E argon windows, Radiant loop runs along outside wall and works it's way to the interior.

I used a Taco Xpump block and tied this into my existing 50 gal indirect DHW for the heat source. The only issue I have is that the aquastat on the indirect has a fixed delta of 5 deg. and I might like to try a larger delta-T on that control to lengthen the cycles on the boiler a bit when I'm only heating the floors.

I was beginning to feel a bit silly for going to all this expense for a couple of rooms that previously were completely unheated (only came up with 2800 BTUH heat loss using the slant-fin program), but let me tell you how nice it is to walk on warm tile first thing in the morning. Besides, the rest of the house is single pipe steam and this allows us to keep the heat set lower (or off) for the whole house in the morning, which has got to be saving some fuel.

-phil

PDM

I think that we both did the right thing, but my opinion is

probably biased!

That x pump is a fancy thing but looks like it is a good fit for your application. I had two pipe steam and a boiler that put as much steam into the basement and up the chimney as it did into the pipes. Now I have a wall hung Trinity 200 with reset control, the aforementioned radiant loops, a hydronic coil in a Spacepak air handler with heat pump. The radiators have been sandblasted, repainted, new unions and 'home run' connections with barrier PEX snaked through the walls to manifolds. The hydronic coil is used when the heat pump goes into defrost or to bring the temp up quickly. The system is controlled by a Carrier TSTAT, set up for 3 heat/1 cool. Below the balance point or if the heat pump can't hold temp the radiators come on.

It's hard to say just how much gas/electric I am saving, but I know I've spent a bunch, learned a great deal, and have gently coaxed an old home into the 21st century.