Replies

1. 
   Guest_ | Apr 03, 2000 06:54am | #3

   *
   Hi Folks,

   Came across a small, compact house with R-30 walls, R-40 attic, very airtight, but it has terrible electricity bills. There's radiant heat drywall ceilings in the place, and I suspect the second floor radiant panels (located on the attic side under 14" of fiberglass batts) are doing a better job of heating the attic rather than the living space below. Besides wind wash (over-ventilated attic) and convective heat loss through the fiberglass, I've heard fiberglass is transparent to radiant heat, so there goes that too. At minus 30, like it was this past January, the meter just spins.... Then again, the refrigerator beside the woodstove is probably doing its fair share of beefing up the hydro bill. What's the verdict out there on radiant ceilings?

   Ross

1. 
   Guest_ | Apr 02, 2000 01:56am | #1

   *Heat rises.Buy more wood for the stove.

1. 
   Guest_ | Apr 02, 2000 04:38am | #2

   *I believe you hit the 'watt' on the head concerning the fiberglass insulation. We have literally thousands of electric radiant ceiling homes in my area. Mostly cookie cutter tract homes. The difference between fiberglass and cells insulation is definitely measurable on a grand scale. Get rid of the fiberglass.Call your local electric utility before doing so. In some areas the utility sponsored and even installed those systems so they need to be inspected prior to shooting cellulose. My electrician tells me that some of these systems may not be safely covered directly with loosefill insulation. Possibly some of those originally installed in the 50's and 60's.I still think it's tough to beat the comfort of radiant ceilings if installed and controlled properly. The icing on the cake is radiant floors using perimeter ceiling heat as the second stage.The reaction time is much faster than high mass floors and you can get twice the BTUH per SF which can be strategically placed on exterior walls where the heat loss is concentrated. BTW, the "Hot Head Syndrome" is real. Your situation in the post above is just one of the reasons why this is true in some cases. The surface temperature must remain unreasonably high for longer periods of time due to backlosses thru the insulation above. The higher the surface temperature, the greater the convective flow to the unconditioned attic space. In most of the older installations I have experienced, the the entire square footage of the ceiling was used and generally they used just one loop. The walls were poorly insulated. They needed high surface temperatures over the entire ceiling to overcome the large losses from the exterior walls.Once these walls were eventually insulated, they were actually over-radiated which would further increase the back losses thru fiberglass insulation above. Most of these systems relied on Bang-Bang control strategy as opposed to Pulse Width Modulation.It is my opinion that radiant ceilings, whether electric or hydronic should be designed with more than one circuit. ie: perimeter AND occupied The perimeter circuit should cover the heatloss directly attributible to exposed walls and the second circuit should primarily cover the upward loss, infiltration load and Operated as a two stage system, this design strategy is extremely comfortable. But, of course if you have radiant floor as the first stage, ceiling heat would only be used as the second stage and would only be needed on the perimeter.That is unless you're like my family who lives in a virtual "heat sandwich" laboratory with radiant ceilings, walls, baseboard and floors[g]. Always a work in progress because I just like the opportunity to experiment with the several combinations.Do these folks a favour Ross and help them straighten their system out. They will be bucks ahead and you will be a hero in their eyes everytime they open their electric bill.Jeff-Too far behind to be reading these posts

1. 
   Scott_Chadbourne | Apr 03, 2000 06:54am | #4

   *Ross,Radiant ceilings are bad news. When I built the house I currently live in 22 years ago, our local REA co-op promoted the pee-wadding out of radiant heat. About 7 years ago all the sheetrock in the ceilings came loose due to the constant expansion and contraction of the heat/cooling cycles. They install the radiant cable over 1/2 or 5/8 kal-kote board and then cover the cables with a 1/2" of plaster or so.It weighed a ton and just sagged everywhere. The blown in cellulose filtered between the bottom of the trusses and the top of the kal-kote board so it was impossible to level the ceilings. Ended up tearing out all the ceilings and installed a geo-thermal "water furnace". It was very expensive but the co-op offered a 5% loan to everyone that was affected. The water furnace will pay for itself this year in energy savings and the house is finally warm in the winter without the $4oo + monthly electric bill. The houses I build in town are on Illinois Power which sells electricity for heating [for all electric homes] at around 2.8 Cents per KWH. The co-op I am on is a little over 8 cents per KWH.