David Anderson said:
One perspective you must take is that this type of heating is not designed to primarily generate heated air. So don’t go looking for large amounts of thermal output. ??? Air does not take much heat to raise its temperature. The specific heat of air is 0.018 btu /cubic foot. 1 lb of water takes 1 btu to warm it 1 deg F. This 1 btu can warm 56 cu. ft. of air 1 deg F.
As the body radiates heat, some of it is reflected back and some of it goes off into space. If you sit by a window in the winter or summer, you feel heat leaving or entering the exposed side of your body. Radiant heat prevents this heat loss from the body by setting up a small radiating field that will warm objects within the room, but not the air. If the air warms, it generally comes from objects (to include the ceiling materials) within the room which become warm and then heat the air.???
If designed correctly, radiant heat will heat the room to comfort including the air so you have to have enough thermal output… if by design, you need 2500 watts to heat an area or room, you install 2500 watts of ceiling heat.
Again, radiant heating is not intended to specifically raise the air temperature like a normal furnace. You will “feel” warmer at a lower air temperature with radiant heat.
The thermostat controlling the room heat senses air temperature, the air must heat up or the heat will never shut off!!! The manufacturer’s give us the crap about lower room temps. If the air around you is cool, you will soon feel cool when the heat shuts off. The infrared radiant heat waves hit the floor, walls, bodies and other objects, turns to sensible heat which then heats the air. You have to heat the air and walls etc, to provide total comfort since human comfort depends on 4 factors:
- Air temperature
- Air velocity
- Relative humidity of air
- Mean radiant temperature of all room surfaces and objects
If you don’t have #’s 1 & 4 at high enough levels, you are not fully comfortable.
The most effective way of testing radiant heating is with an infrared camera!
I feel the best way to test radiant heat is to expose the wires at the room thermostat and check the current flow. No flow, broken wires, if all other items check out (good t’stat, voltage, connections). Doing it this way allows you to check if enough heat is installed in the ceiling or if all the installed panels (some have parallel resistive elements) are intact. You can do a quick mental calculation as to the # of watts needed to heat the room and then calculate the actual operating watts from the amps and voltage (W = I x V). If the measured value is too low, some of the system is failing or… it may have been improperly designed. In either case, there may not be enough heat installed for the area.
Facts about some radiant ceiling heat systems:
- Some Flexwatt panels have been implicated in fires. See http://www.okvalleyinspector.ca/reports/ceilingheat.pdf . In Canada, these were mostly installed in Quebec and British Columbia; don’t know about the US. The company contact is in the US so you can expect some to have been sold there.
- The Thermaray panels mentioned as safe in the above recall were safe but had their own other problems for a period. Their construction has fine heating wires embedded in parallel in specially sized pieces of drywall (14 inches wide). The drywall heating panels were then installed in between the ceiling strapping and covered by the finish drywall. After a period some of the fine wires broke leading to loss of heating capacity. The breakage was not consistent so each room has to be tested individually to determine how much capacity, if any, was lost. These panels were manufactured in the late 1980’s and sold in the US and Canada.
- Don’t know of any problems with the ESWA. Installed it in the last house I built for a client in 1987. Haven’t heard of any glitches. Have no experience with Safe-T-Flex.