Radiant Ceiling Heat

I am a little “out in the cold” about radiant ceiling heat. Could someone please tell me what I am looking for in terms of accepted operating temperatures on the ceiling when there is imbedded heat cable? I’ve never been able to find that information on the net, and I’ve had a couple of people ask me lately how hot the cables really get. Also, what guidelines are you guys using to differentiate between cosmetic and structural plaster cracks (seems inevitable with the radiant heat)? I usually call it as a problem only if the plaster is chipping back from the crack. Thanks… I know I’ll get nothing but the best answers to my questions here!

Harry Hull
4 Corners Inspections, LLC

I searched radianty ceiling and found these.

http://www.nachi.org/forum/showthread.php?t=16767&highlight=radiant+ceiling

http://www.nachi.org/forum/showthread.php?t=14818&page=2&highlight=radiant+ceiling

http://www.nachi.org/forum/showthread.php?t=7323&highlight=radiant+ceiling

Heat cables would not cause “structural” issues in plaster or drywall.
The best time to test heat cables is in the winter months.
With heat cables particularly the ones buried in the plaster can develop hairline cracks, and/or ghosting.

The newer heating cables are in mats placed on the attic floor against the drywall.

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.

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.

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 most effective way of testing radiant heating is with an infrared camera! :slight_smile:

I have inspected plenty and the old way with spray bottle was slow .
I now use a laser thermometer and it works very well for me .
You also can confirm how they are working with a Clamp on Amp meter in the panel .
Of course if I had an Infra red Camera I would be telling people you need to get a thermal image
.

:slight_smile:

That works as well as anything!

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:

  1. Air temperature
  2. Air velocity
  3. Relative humidity of air
  4. 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:

  1. 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.
  2. 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.
  3. 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.

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.

And how do you plan on doing that on a home that you and the client do not own? Well beyond the SOP.

Unless you plan on do a full heat loss calculation your theory is not correct, because you have to take in to account insulation levels and tightness of construction.

Raymond:

I was speaking in a general sense. I don’t carry a clamp-on current tester. If I find the thermaray system, I call a certified electrician in. I feel the current test is better than infrared as it gives the actual working wattage.

There are some rulles of thumb that have been developed by electricians for certain styles of house construction in our area. Older 2x4 walls with R12 and R30+ ceilings would be 10 watts/sq ft with average sized windows. Newer R20 walls, R40 ceilings with casement style sealed glass units would be 7 watts per sq foot. If you find 20- 50% lower wattages than these, there may be problems. Notice that I said our area; northern Ontario would be different as would be Victoria, BC. Local electricians would have developed their own rules of thumb.

Yes it would be better to do the whole heat loss study as required by CSA F280 in Section 33 in the building codes (Canada) but we have only so much $$$ to spend in a home inspection. In litigation, I would do the full meal deal!

We don’t test concrete strength and look for lumber grade stamps in regular home inspections, do we?