Floor warming vs radiant heat

Fetzervalve

What is the distinction between floor warming and radiant floors as a heat source?

Does a radiant job that can't produce enough BTU transfer default to a "floor warmer"? Or are the floor temps lower by design?

I have solid oak floors, I have seen that a max of 85 is recommended - is that the same for warming, or is it typically lower?

Thanks!

kevin coppinger_4

floor warming....

is generally going to give you just enough heat to take the edge off while not being enough to heat the whole room at low outdoor temps. A significant source of suplimental/extra heat would be needed. The max floor temp. for wood floors generally is 80F not 85F.At 85 on wood you run the risk on warping and buckling.kpc

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Art Pittaway

85F is Design Condition

A Radiant heating system should adjust somehow to meet the btu load/loss of the building. Some systems go on/off at a set water temp and others use methods (injection or mixing valves) to vary the water temp. Most of the systems I designed never got to 80F floor surface temp. At "design" the floor surface needs to be hot enough to meet the BTU loss of the room. Northern Illinois it is usual practice to use -10 @ 10 mph wind as Design, that happens for a few days every few years. A well designed room is toasty with about 75F floor temp. when it is 20F outside. Most of the shops (concrete floor) I did would set the thermostat at 65 (comfortable for a shop) and the floor surface would never go over 75F when it was 20F+/- outside. A "floor warming" differs in that it is not controlled or sized as a function of heating, but call it surface conditioning. An unheated tile floor at 65F will chill anyone, so by raising the surface temp to a setpoint, say 70F - 72? it adds a little heat to the room but mostly it makes the floor comfortable to the feet. Heat goes to cold and the closer your floor temp is to your feet temp, comfort!! How about your shower wall, Ouch!! or Ahh!!? I set up quite a few with a two stage controller set in series so when the outside temp went below 65F the floor warming was enabled, then the controller used a sensor in or under the floor to bring it up to a comfortable temp. Most people don't want it warmed in summer. I hope this helps. Art

Paul Rohrs

BTU's

So, as system designers, how many btu's per sqft do you calculate for floor warming as opposed to primary heat?

Regards,

PR

Mark Eatherton1

Max wood floor temps...

My partner was at a house the other day investingating a poor heat call. He found that the new HO had decided to put down some real nice thick woven indian rugs. He lifted up the rug and shot the floor below. I think he said it was at 105 degrees F, and it was in FINE condition.

If hardwood floors are limited to 80 or even 85 degrees F, how come they still allow people to install them in areas with South facing windows? I've seen temperatures as high as 140 on HW floors in the sun without RFH...

If the wood is fully cured, the sub floor is dried to ambient humidity levels and the internal humidity is controlled within reason, the floors will be fine.

I think the hardwood people picked up on the RPA's maximum recommended floor temperature and decided that that was a good number to stick with. It's obviously a false detail as proven on a daily basis by HW floors in south facing rooms.

ME

Art Pittaway

Nice question...!

Since I worked with the former Heatway and went by most of their guidelines, I was looking for 12 - 15 btu/sqft, and that was probably high. But, with floor warming you can't put hose on 24" centers and downrate the system to XX btu/sqft. The btu number is more of a guage for boiler (water heater?) sizing than anything. I believe the even heating of the floor (same temp everywhere) still dictates that hose spacing is virtually the same as a heating application. The first reaction is $$$ and that is what separates the "I want it" customer from the "I want and can afford it" customer. I did a rehab on a house that already had forced air and lots and lots of white tile in the kitchen and dining area. The new homeowner said, "I walk around in my bare feet and I don't want them cold in winter. Never flinched at the price, he got toasty floors that came on in the fall and off in the spring. Art

hr

I'm not sure

you could put a BTU/ sq. ft. number on the difference between heating and floor warming.

Heck these days 15-18 BTU's per sq. ft. will HEAT most well constructed homes.

Floor warming is a common arrow in my quiver. I add these to currently heated homes, generally FA. mainly to add a few degrees to a seemingly cold floor, although most are ambient room temperature when you actually shot them

I think the control is the key to floor warming. As such a stat that can "watch" floor and air temperature works best.

tekmar and Wirsbo offer a nice dual stat, although I hate the small enclosure size and wiring issues Hard to hold the thing on the wall with all those wires! Give us a backing plate with wire connections. Please

Anyways, this type of control allows the owner to adjust the floor temperature to their preference. I generally have then close off the FA registar in that room and let the floor handle the load.

It's important the owner/ operator understand the control operation and concept of floor warming.

I use a basic setpoint control with floor sensor on my own homes floor warming area. It does take some tweaking from season to season, however. The dual sensor controls simplify this with their max setpoint control- ability.

I still tube my floor warming 8" or even 6" on tiled areas,on center to eliminate the stripping effect as much as possible. Helps keep supply temperatures cooler to prevent floor surface temperature over swing, also.

hot rod

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Fetzervalve

Warming control for water heater

Is there any way to get control of a water heater used for warming or heat other than circulator on/off? Sounds like the outdoor reset - floor temp etc. are very nice, but are they only for boilers??

Thanks!

Mark Eatherton1

Yes, but...

the warranty will be voided as soon as you do it. You can buy a normally closed solenoid gas valve and pipe it in series with the snap acting aquastat. It goes between the S.A. aquastat and the burner. You are not affecting the pilot safety circuit, and you can't turn the heater any higher than it would have gone anyway, so it IS a safe application, but nonetheless, your warranty is void.

I've done this and used a simple tekmar outdoor reset controller and it worked quite well. The basic design of a water heater still dictates that it is an energy hawg, but at least with this modification its an energy efficient energy hawg:-)

Even with this modification, when I installed my Munchkin T50 with Vision 1 controls, and displaced the "energy efficient" water heater, I've seen a 30% reduction on energy consumption. And its been colder this year than last!

ASCO (Automatic Switch Co.) was the brand I used.

http://www.ascovalve.com/

ME

hr

The stat I mentioned

would give you the same function on a WH, as far as switching the pump on and off based on floor/ air temperature. On a regular WH it could not control the gas burner, however.

If you use a power vented water heater they have a 120 or 24 volt circuit you can interupt to switch on / off the burner.

Some say they are a bit more efficient as they don't have a flue through the roof continually sucking the heat up, thus effecting standby loss. Most are PVC ventable, also.

hot rod

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Art Pittaway

HR your right

about the BTU load numbers, 5 BTU/FT is maybe more like an average, but the heat source target size has to come from somewhere, and sometimes it's an educated WAG.

When it comes to waterheaters for really small loads I still like the 5 gal electrics. Energy cheap? NO!, but energy use is always 100%. When the floor is satisfied everything shuts down but the thermostat or temp. controller. No pilot, no gas, no flue, no buried wires in the floor. Did a 1/2 court basketball court for a guy that wanted it for his kids. Nowhere to vent, period. Electric W/H under the stairs does the job just fine.

Reset is fine for a boiler or a job with a large temp. swing, but I question the cost in controls and complexity for a floor warming or "simple" heating install. Like it was said, closer spacing, lower temp. water and you really don't need reset. Didn't someone say the right answer is always,"It depends". Art

Fetzervalve

Outdoor reset?

Perhaps I don't understand the outdoor reset, I thought it was able to change the water temp for outdoor temp changes.

Mark Eatherton1

Rules of thumb

Generally speaking, each degree F difference between floor temperature and room air temperature will deliver 2 BTUH/square foot. So, say you want to maintain the floors at 73 degress F, and room air temp at 70, then the floor will deliver 6 BTUH per foot square per hour. It may require more than that to get through all the resistance valvues, but thats what it will deliver.

Your mileage (BTU/sq ft /hr) may vary depending upon your driving (resistance values placed on top of the emitting surface) habits:-)

ME

Fetzervalve

Outdoor reset - define?

Perhaps I don't understand the outdoor reset, I thought it was able to change the supply water temp depending on outdoor temp changes. If so could it be adapted to a water heater?

Mark Eatherton1

See the post above that sez \"Yes, but...\"



Outdoor reset will adjust the temperature of the water upwards as the outside air temps fall. Mine was set to start at 70 degrees F when the O.S.A. temp was 70, and increase the supply water temp by one degree F for each degree F the OSA fell below 70. Its max water temp was 140 degrees F.

Gas fired residential non draft induced water heaters come with a manually adjusted gas valve. My recommendation would allow you to turn the heater up and down automatically using an outdoor reset controller.

ME