ceiling panel heater (electric resistance)
Does anyone have experience and brand recommendations for low-temp, low-wattage (probably well under 1000 W) ceiling panel heaters? That is to say, indoor electric-resistance radiant heaters that run off 120V power.
I was thinking about slightly undersizing my ductless mini-split system and using a handful of electric resistant heaters to supplement on, say, the 5% coldest days. These heaters could also help smooth out temperature gradients throughout the house, and finally can also serve as backup heat if the mini-split fails altogether.
Mind you, I know that many mini-splits have electric resistance heaters built-in for dealing with sub-0 F conditions. But this town really bottoms out at 5 F, so I’m not talking about that kind of functionality.
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Replies
David,
Have you thought about using a wall mounted plug-in model you could remove during the rest of the year? That might be a lot less intrusive than a ceiling mounted heater.
https://www.convectair.ca/en/products/120v-plugin/apero
Radiant ceiling panels are silent, and don't protrude into living space. Also, they don't require moving air around with fans.
David, I don't have experience with radiant ceiling panels, aside from seeing old ones under failing paint on a few renovations. I understand not wanting the fan of a Convectair or similar heater.
I had similar goals for a small room in my house, and decided to try an Envi heater: https://www.eheat.com/envi-high-efficiency-whole-room-plug-in-electric-panel-heater-hh1012t/. They don't have a fan. They do project from the wall a bit, but the design is sleek and low profile. They distribute heat via passive convection, so you get better air circulation than you would from a true radiant heater. In many ways they work like electric baseboard heaters, but look better. They also cost more, but are still very affordable.
I don't think Convectair heaters have fans. Mine don't, in any event.
Also worth considering that wall units that get hot are not kid-friendly. Heck, even adults that aren't paying attention...
Stephen, it turns out that Convectair has a wide range of products: https://www.convectair.ca/us/products. The only ones I've looked at closely had fans, but they also have a line of "natural convection" models that don't have fans.
David, the surface of my Envi wall-mounted heater never gets hot enough to be dangerous. The wall above it gets pretty warm but not enough to burn. I'm not trying to convince you away from ceiling panels; it looks like there is a wide variety to choose from. Just trying to clear up any misconceptions about wall heaters.
David,
I specced radiant cove heaters on two projects and one homeowner went ahead and installed them. To me the "radiant" aspect of the heat seems a bit overplayed. I don't notice any appreciable difference between the way the heat is delivered from any other resistance heater. It is nice that they are out of the way of furniture (and kids), but they are a lot more intrusive architecturally perched up near the ceiling.
Given the premium in price between them and baseboard heaters, and the lack of real difference, I'd hesitate to recommend them to a client again.
Another option for providing small amounts of heat delivered to more places in a building than is possible with minisplits, while retaining the superior efficiency of minisplits, is a air-to-water heat pump such as chiltrix. You can put minipslit-like fan coil units where you'd put the minisplit heads (with more options for small low-profile units), and supplement with small panel radiators where you want smaller amounts of heat delivered locally. Radiant ceiling panels are also an option.
I don't think undersizing the mini-split system makes sense, I would suggest going with a correctly sized mini-split system. If you want some electric resistance backup and consistent temperatures (may not be an issue), I can understand planning for that.
We primarily heat with a mini-split and have 500w Stiebel Eltron wall heaters (240v, hard wired) in a few areas (bedrooms, bathrooms). We only use them when temps are forecasted to drop below -10F, but they aren't necessary.
If I could do this over, I would just do the mini-split and wire some extra 120v outlets where I might want some Convectair (or other) plugin wall heaters. See how the mini-split works out: if it meets your needs, you're all set.....if you need more comfort due to temp gradients, buy a few wall heaters.
We heat with minisplits. Since we didn't really know how well the heat would be distributed, we installed a Convectair 240 volt wall mounted heater in our guest room/ office/ tv room. The only time it gets used is when my daughter visits. She apparently didn't inherit the hardiness genes from her parents, even though she grew up in New England. For everyone else, the room stays warm enough.
The Convectair unit is silent and puts out a decent amount of heat.
I agree with Brian that undersizing the minisplits doesn't sound like a good idea and will probably use more electricity.
I did quite a bit of research into radiant heating when I was considering heated floors for our new house build. From what I gathered, the heat you feel from radiation is a combination of all of the room's surfaces. Therefore, a relatively small radiant panel at a relatively low temperature will have only a small impact on how someone feels in the room.
Using the whole ceiling as a radiant panel would work. There are companies developing 4x8 hydronic sheets that are jointed and taped into the ceiling like drywall. Here's a radiant ceiling design document from Uponor. It may not be what you're interested in doing, but it has lots of charts and formulas that will help you determine the level of radiant you need to accomplish your goals:
https://www.uponorpro.com/~/media/extranet/files/cdam/cdam_manual_7thed_0711_ch9.ashx?version=072920111126
Jon's observations match what I found. As per the manufacturer's instructions we mounted the radiant cove heaters on the wall opposite the window. compared to the effect of a baseboard heater below the window, the radiant coves don't mitigate the cold feeling nearby half as well.
If someone sits near a window, a heater *below* the windows will typically significantly reduce downdraft discomfort and to a lesser extent, reduce radiant discomfort.
https://www.deelat.com/hvac/heaters/electric-wall-heating-panels/radiant-electric-wall-heating-panel-595x1195x22cm-720w-110v
The above has lots of area and minimal watts (.67W/in2) but it's not clear if it is a hazard.
High mounted "radiant" panels are going transfer a lot of heat via convection and it will be stratified (vs well mixed). Little to no benefit wrt window comfort.
Interesting, guys. Thanks for the feedback. Is there really that big a comfort issue near modern, triple-glazed windows? I wasn't really thinking about that.
David,
I have lived with all manners of heating formats except mini-splits. My current home is 100% radiant cove heaters from Radiant Systems Inc in Nebraska. Comfort Cove might be another google term. Many points have been touched on already, pro and con. Here's my take and how I came to my decision.
I grew up with coal/wood heat in part of the house, hot water baseboard in the "new" part. I hated taking the ashes to the garden as a kid and my dad hated bleeding the baseboard system annually. The single pane windows were always cold even above the baseboards which ran pretty much every inch of exterior wall. The "pink, pink, pink" noise of the copper fin pipes expanding at least meant the heat would arrive in an hour. A 60's renovation of the old part brought us radiant ceiling panels which were awful. The poor insulation in the old house area amplified the highly directional characteristics of putting heat in the ceiling. Cold walls, colder windows, freezing feet under the desk while baking the top of ones head. The ceiling location only warmed the tops of things. The heat losses far exceeded the input from the ceiling so the room never "soaked" in enough heat to become one temperature. And the paint peeled.
After growing up and spending 40 years with all the dust, noise, uneven distribution of forced air heat homes, I chose to go all in with cove heaters for our 'new pretty good house'. I looked at mini-splits, but our home is quite the opposite of open floor plan so the fit was not good. Also, the local installer options were outrageously overpriced. For operating cost efficiency, they would by far be the best choice for the many reasons enumerated here on GBA posts. Still, my wife didn't like the look and needing 6 heads for our plan didn't make good sense.
Two years into living with my decision, I can say radiant electric would be a helluva expensive way to heat if you weren't super well insulated. Fortunately, I am, and the Alpen windows make the "heat source under the window" motif a non-issue. Electric points for future baseboard heaters under the kitchen nook windows have proved unnecessary. On a -5 F night the center of window still held at 60 F, though the edges were showing some condensation by that point, which probably goes to show why triple glazing is a major comfort booster. My old double glaze windows in the previous house would go to 45F in the middle and 35F at the edges at 0F. If you are not planning on triple glazed windows, you will be cold next to them and the cooling waterfall effect will cycle the room air.
I will point out that the sensation of radiant cove heaters is quite different from forced air (or mini-splits I suspect). The air temperature is never more than a degree off from thermostat settings which at first sounds correct. The sensible effect is the rooms always feel a little cold to me though my wife thinks 70 is too warm. I am badly balding so my answer is to wear a cap inside. Both mini''s and forced air furnaces provide their warming air well above the thermostat setting. It may be that presence of warmer air which makes a room seem more comfortable. As a hairless type, past experience makes me think this is valid, since the air is probably averaging out to several degrees above the wall setting when the fans are on. However, neither of us miss the whooshing noises and redepositing of dog and cat hair onto every surface. Filters not withstanding, the dust bunnies were always on the move. Mini-splits might amplify the warm head effect due to the higher point of air distribution. Dust bunnies might stay put under the sofa.
I would disagree that they are any uglier than mini-split heads, baseboard heaters, or wall mounted heater panels. They have just become part of the "wallpaper" of awareness, much like any vent or light switch does. We don't worry about blocking vents with furniture or rugs, we don't have mobile dust bunnies, and best of all each room has their thermostat, so everyone gets to sleep at whatever temperature they like. The whole house, heater elements and wiring was done for less than a quarter of a small forced air system. We did not plan for or need air conditioning due to the local environment. Dryer air and 40 degree temperature swings allow us to bank cool night air in higher mass walls which carry the house until 7pm. The house is blessedly quiet save the few small ventilation fans which cycle much less often than a furnace.
Cove heaters can be had in 120 or 240 format, so the bigger issue is space for breakers and wire runs. Plan on 150 watts per foot of heater. We have both due to that issue and both work just fine. The actual heat they put out is pretty long wave IR. You can feel the heat out to about 2-3 feet from the source. After that it is not noticeable. There are limits for proximity to ceilings and wall and window treatments. The cannot be painted , but do come pre-finished in a small range of colors. Installation is simple, but the front special paint cannot be touched by finger oils. (at least until they have run for a while) Only one out of 15 ever made noise and that was just a small ticking as it slid on the hanger. A tiny dot of molly grease cured that. They are not meant for rapid warm up of even small spaces. Think of them as slow cookers, not microwave ovens. A small air based bath heater or even a wall panel type will produce faster results. Just a heads up on the many wall heater panels I looked into and rejected. High failure levels seem common and much higher surface temperatures are inherent in this style, even when combined with "safe touch" panels. The wall directly behind the cove is not very warm at all and the ceiling is not a whole lot warmer.
All that said, they are still resistance heaters and consume electricity accordingly. If I had had an economical option I would probably have done mini-splits. I would not mount them on the house from what I have heard. I am cursed with very good hearing so the low level vibration of compressors is my bane. Hope this helps in your decision.
When sizing the resistance heaters, run the heat load numbers and don't oversize- if anything UNDER size it by at least 25% from the full design load, or even half. It's too easy to become complacent and leave the resistance heaters running, and they will carrying the bulk of the load rather than letting the heat pump do the heavy lifting.
Enabling the resistance heater theromstats with occupancy sensors or timer switches is one way to get around that potential efficiency pitfall.
Roger,
I always appreciate your detailed and thoughtful answers.
David,
You are probably right about the comfort issue. If you prefer the radiant cove heaters and don't mind the up-charge, I'd go with them.
With good windows, under-window heat might change from 10% dissatisfied to 20%. Most people will be satisfied with either. Best to put in actual scenarios below:
https://www.payette.com/building-science/glazing-and-winter-comfort-tool/
Roger, thanks for this timely review. I am considering some supplemental heat just before finishing my electrical rough in. I ruled out baseboard heaters, and was almost settled on adding some electric wire heat on the concrete slab. The downside to that is fairly high cost and labour, plus it necessitates putting tile on the floor whereas we'd previously been considering a polished concrete floor. One question though, what exactly is the difference in technical terms between one of these Cove heaters and a baseboard heater? Seems almost like it's just a baseboard heater that has been mounted high on the wall.
Trevor,
In theory the cove heaters transfer their heat to a metal plate so that more of it is radiated across the room to colder surfaces, as opposed to warming the air as baseboard heaters do. The question is what percentage of the heat is experienced this way, and is it enough to be substantially different than a baseboard or wall heater?
Finned baseboards heat primarily with a high-temp column of air convecting through the baseboard, and very little direct radiation.
Where there is sufficient wall-space, low temp panel radiators on the wall at human-height provides more comfort than cove heaters. Panel radiators heat the space more quickly since they too will convect, but at a lower temperature, and with a greater fraction of the heat transfer by direct radiation. Sized correctly this is the next-best thing from a comfort point of view to radiant floors & ceilings.
Cove heaters operate at a higher temperature with the heat transfer being primarily radiated, with comparatively poor convective heat transfer.
Roger # 15 makes a very good point about heat loss associated with radiant ceiling panels. The higher Delta T and thermal bridging of ceiling joists will require optimum attic insulation. This should be considered in the decision making.
I looked around at radiant panels previously, and was turned off by two things. One, they get hot enough that you have to keep furniture (and people) well away from them, effectively using up a huge amount of floor space and can be a source of accidental burns. Second, I couldn't find any that operated on 240V. That means twice as many or twice as big power wires, which doesn't make me happy.
I just spoke to a guy at Comfort Cove, he estimates 90% of the heat coming off it is radiant. I don't know what he bases this off of. Seems a little optimistic to me. I'd be impressed if it was even 70%. I think ASHRAE's definition of a radiant heating system is >50% of the heat coming in the form of radiation.
Edit: Some further reading leads me to believe that 90% is not all that unreasonable.
I don't think the surface temperature on a cove heater is hot enough to produce > 50% radiant.
In the 700W range, I wouldn't be very concerned about wire size.
I don't really follow the logic that the temperature is too low to produce >50% radiant. In floor heating has a surface temperature below 86F, and those are considered to be majority radiant heat output.
Run heat load numbers on the rooms- you don't need gobs of power or high temps. You can even run them on dimmers if you want to run an oversized cove heater at lower temp.
700 watts x 3.412 BTU/hr per watt is 2400 BTU/hr the heat load of a fairly substantial room in a higher-R house @ +5F.
Unlike floors, cove heaters have some slope to them and convect a decent fraction of the heat, but since they're not very tall and usually located near the ceiling the total convective flow is pretty limited. Panel radiators will usually be subtantially cooler.
Here is a case where "radiant" panels were found to be ~40% radiant. Note that this shifts slightly as panel temperature goes up.
https://www.isiaq.org/docs/PDF%20Docs%20for%20Proceedings/8H.2.pdf
But OK, some other sources have reported 67% radiant for walls. Even that leaves a lot of convection that can put heat in non-optimal places.
Given that the text and the figure caption in the reference disagree about which curve is convection and which is radiation I wouldn't put too much faith in it.
In a well insulated space, the mean radiant temperature will be pretty close to the air temperature anyway. The ability to make people comfortable by elevating the MRT to a comfortable temperature without elevating the air to that temperature really only works when the space is not well insulated, or in a huge space like a warehouse that is not fully heated. So I don't think it's worth worrying too much about what the ratios are.
If the heat is coming from the floor, I wouldn't care about the ratio at all, because convective heat will heat the air which will rise and circulate around the room. In the case of the cove heater, it would be really undesirable to be delivering a lot of hot air right at the ceiling.
That paper is awful. Not only did they confuse the two curves, that graph doesn't even have the x axis labelled or a title. It would fail in a junior high school science class. I am guessing it's unpublished and not peer reviewed.
More answers since I checked in so my following epic entry may not be entirely relevant. I would say that convection is not a large amount of the cove's output based on the ceiling temps mentioned. I was told to think of them like flourescent lights when placing them. The beam is wide and diffuse and our 25 x 11 kitchen/nook with windows covering at least 50% of two walls does just fine with one 450W and one 750W cove located 9.5' up the wall facing the windows. The ceiling pitch is about 4in12. Contrary to Paynette or whatever the link was, not even 16% of me is unhappy next to the three large windows on the NE corner where the table is. Hope the long winded post following is helpful to some.
Just back to relate some of my experiences and add a few thoughts. I chose the cove heaters on faith, hope and a prayer after finally getting a ridiculous quote out of the one local vendor who even knew what a minisplit was. My electrician for the new house recommended cove heaters which he had put in many homes high in the mountains with spotty traditional heating systems. He got me a sample cove heater to audition which I placed in our prior living room. My wife and I were both wondering if it was actually on at first, as the output is not at all like the wall type panels.
Having just measured best I can, I disagree that cove heaters run hotter than wall panels. I measured one cove in the bath directly on center over the embedded heater bar at 325F, the edges came in at 310F. The wall behind the unit was 86F and the ceiling above the unit ( 7") was steady at 101F. The panel heater we use to use in the old bathroom came in at 350F on the face side and 140F on the metal casing on the back which allows for mounting to the wall with only a 1/2" gap. That will make for one toasty wall. Convected air above the unit gave unstable readings since I am unstable, but easily in the 100+ range. We stopped using the panel heater in part because the toaster effect was pretty pronounced on the front side which is even more risky at bath time. Best I can tell, the convection aspect of the cove heater is by far the smaller contribution to heating. Maybe if I was 9' tall I would sense some stratification (and hit my head on the fixtures), but we really do not have the cold ankles effect that the old ceiling panels from the 60s produced. By the way, they did come with insulation on the backs, though pretty skimpy amounts.
Out of curiosity, before switching on the heater, I measured the surfaces in the room to see what kind of variation existed. There was almost none. All surfaces regardless of material came in between 70-72F. I suspect more variation was introduced by my having to handle the sensor than actually existed. Glass, tile, resin sink, metal cabinet and drywall all measured the same. Interior and exterior walls were the same, which is a unsurprising as winter here has been way warm. Have to check again if winter gives us one last freeze. I mention all this to highlight the "slow cooker" nature of the cove heaters. If the power goes down for 18 hours like it did once, the recovery rate for coves is pretty slow. Since the house is insulated well above code, the drop in the house was only 4 degrees. Despite being 10F or less outside. You don't do set back thermostats with coves, you aim for one point.
Also want to comment on floor or ceiling radiant with water or wire. I started out very much wanting radiant floor heat. Silent, even, toasty footed radiant floor heat. As a test, I took advantage of a needed kitchen re-tiling in our drafty 30's house to embed a small wire based kit to show my wife how wonderful it would be. Scotsman that I am, I only placed the wires where she would normally stand by the counters and under the table area. This proved very revealing. The heat print of the wires was easily discernible when shoeless. Even more so under the table where I had doubled the spacing of the wire pattern to see if I could cheat even more square footage out of one kit. The heat spread either side of the elements was quite limited despite being porcelain tile. Further, the actual temperature necessary to be perceived as "not cold tile" came in at 80-84F. Driving the wires to warmer floor temperatures did "smoosh" the cooler gaps together, but it also overheated the room despite its being historically cold. It became apparent that the wire spacing would need to be closer than I thought which meant massively more wire footage per room. I also experienced one floor sensor failure and two failures of the wall thermostat/controller. Not an encouraging record for a heating system for trapped under the tile. The clunky methods of embedding the wire also makes floor planning awkward if one is to avoid toe-stubbing transitions. Depending on adjacent flooring choices, it can be necessary to specify different subfloor heights. I also realized that any future flooring changes could only add more flooring over the tile. This would mess up any transitions between rooms.
As the new house design progressed, I looked into gypcrete with tubing, Warmboard, staple up with heat spreaders, the then new thin film floor heating materials and a raft of variations. I finally forced myself to do the math regarding heat loads and realized that my loads would be so small that neither water or electric wire based systems could run at a cozy foot temperature without over heating the house even with subzero weather. I was also faced with material costs of 5-11 dollars a square foot, to which I needed to add labor and handling charges. My flooring material choices became driven by my choice of wire or water. Failure with a water system could be pretty disastrous no matter embedded or staple-up. Both types can make future remodeling very problematic. Initially the advent of functionally useful under 0F mini-splits seemed the perfect answer. Where we built kinda dashed that option as my wife did not like the looks of the heads and our floor plan is not open in the least. So that is how we came to have cove heaters which as noted also cost only about $5000 for the whole house installed cost above the normal wiring planned.
Our heat use for first season was approximately 1.25 watts per sf per degree day. Second season has been very mild so we are under 1w/sf/dd. I do pay dearly for the heat I use on a BTU basis since the source is straight electric. The minisplits would have been cheaper to run and give me air conditioning. By good fortune and hopefully by my design, we have found the cove heaters are perfect for us. As I mentioned before, the design in conjunction with local weather/humidity allows us to avoid AC. Of course, I may be in for a terrible surprise if we tip the median world temps up by 2.5C.