Ceiling mounted radiant heaters
I am building out a wood shop which is a simple 30’x50′ rectangle with 12′ walls, a flat ceiling and concrete floor. It is expected to meet Passive House thermal and air criteria. Seeking information/experience/advice with use of ceiling mounted radiant heating panels. The safety they offer in a space with flammable particulates is attractive. The few companies I have searched do not readily offer information on sizing or number of units for a given space.
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I specified them for two projects. On one they were used, on the other the owner balked at the cost for what is something very close to an electric resistance baseboard heater.
My experience with the installed units were that the proportion of radiant, rather than convective heat, was too small to appreciably distinguish them from other electric heat sources. Their main benefit was being mounted away from there they would interfere with furniture.
Radiant Cove heaters, like other electric heat sources, are sized by their output in watts. The size necessary to heat a given space depends on not only the size of the room, but the insulation levels of the various building assemblies. You need a heat-loss calculation to determine what that is.
There is the old school radiant ceiling heat or newer panel systems.
The old school system is not popular today but it has been around since the 50s. You may find this link helpful.
From a practical point of view I see no reason the floor systems would not work on the ceiling. The floor systems wires are thicker but charged wires looks to be surrounded by a grounded wrap making it more difficult to damage and very likely to fail in a safe way.
If you can locate someone who has experience installing the old style system the costs may be very reasonable.
For what it is worth, I am currently maintaining about 65F in my basement shop with one 900w cove heater from Radiant Systems. To be sure, with uninsulated 8' ceilings which are the heated first floor of the house, my real load calculations would be tricky at best to figure out. The total area of the basement is approx 1300 s.f. with the more remote parts drifting down to 60F.
Once I get organized enough to set up my lathe, I may well want a bit more heat in that area. The main house is entirely cove heaters which allows room by room control which keeps my wife happy. A mini-split was ruled out due to insane costs locally and my wife hating the wall units and fan noise. The house is not meant to be Passive level, but overall energy numbers seem to be pretty consistently a bit over 1btu/s.f./degree day. The efficiency of using mini's is absolutely undeniable. In your case, the value of having AC as an option could be huge.
Malcolm has already noted most of the cove heater features. With your very tall ceilings it would be important to know some other points. The convection component is much like you would expect from a baseboard heater, so the warm air will be rising to 12' and sit well over your head. The radiant component is best imagined as a rather directional strip light. The preset mounting angle works out to be perfect for my shop needs when set 7 1/2 feet up and about 8' from the workbench. I am balding so when my head gets closer than 5' to the cove heater, I can feel it rather like sunshine. It is very important to know that the radiant component warms objects not air, so the air temperature will not be different than what you set. Warm air devices logically will burst deliver very warm air, which can feel cozier. You must not place the thermostat in a location where the cove heater will project its warmth at it or will have problems.
The warming effect is very slow compared to heaters with fans that blow hot air. It took my shop almost three months to stabilize at 65F after being 60F for the first two years. As my shop is in the basement and I chose to exo-insulate the entire foundation and floor slab, I suspect that much of that time was spent with heat getting stored in the 60 or so tons of concrete that surrounds me. You may have less of a lag since only the floor is concrete.
If you go with cove heaters, I suspect you will need 5-6 6' units staged in a way that correlates with your work patterns and machine stations. You will need to deal with the local electrical inspector on how to handle placement on anything but a normal wall. Maybe a faux wall set 12' out from one side would break the 30' width in a useful way. Or perhaps combine a centrally located dust collector muting room with code approved mounting on the outside of the walls. The heaters will not run more than needed, so any apparent over sizing is not terribly important. The beam spread will be a more useful aspect to consider, which is not meant to contradict Malcom's recommendation for an accurate heat loss calculation. It is just that some oversizing with cove heaters is very cheap and not really a waste of efficiency. I am assuming that you have already sized out the panel and feed wires for big amperage.
In my prior life, one of my clients sold commercial and industrial vacuum systems. The engineer I worked with was quite adamant about air quality in work spaces, providing me with horror stories about places I can't name. I will urge you to be very vigilant about dust control down to the 1-2 micron levels. There are many terrible dust collection systems sold. An under played side effect of poor dust management is rapid onset of lung issues in retired woodworkers. The same engineer told me the quick rule is, if you can easily see it, it isn't harming you. The stuff you barely see is staying airborne the longest and will penetrate the deepest into your lungs. If you can see smokey sunbeams in the shop, you have a serious problem.
I have a very mixed attitude toward the hanging air filters pushed at woodworkers. Ostensibly, they will purge the air of the small harmful stuff. What is overlooked is the downstream blowing of the units, which can lift and circulate the small dust particles accumulating around the shop. Not every single cubic foot of air will magically go through the unit obediently, so blowing a 400-600 cfm fan across the shop can be problematic.
That said, you might be able to use the hanging fan cleaners to your advantage. With 12' ceilings and a stagnant layer of warm air hovering up there, a forced exchange of strata might be beneficial on two counts. I can think of a few ways to hang or modify the units to best effect, but I need to stop droning on. Simple ceiling fans would suffice, but not help air quality.
A few last things to consider when doing your calculations. The tools of course give off some heat, lighting if LED much less, how many people will get to share your enviable shop, and not to be overlooked, the main dust collector for the tools. Unless of course if you are going old school and hands only. The heat output of a 1200cfm dust collector is not something I have put a number to, but I can advise that churning air through them is work and work is energy. If I run mine for more than an hour, the air temperature will go up quite noticeably.
Maybe someone else on GBA can put a number on the heat output.
Consider the doors to the shop and how often you plan to open them. If you are in a cold zone, the penalty for a big air change and cove heating is a longer lag before it "feels" warm than you would have with a heated air system. Not a huge issue, but one to think about.
And finally, (really) I don't recommend the big panels that form part of the ceiling or are hiding behind ceiling surfaces. At 12' up they will be like a dim winter sun and besides the backs are just heating up the insulation above. More on that later if needed.
Happy shop time, I really miss having 12' over my head.
Having lived with cove heaters Roger has noticed a larger radiant component than I have just visiting a house with them. I should also say that although they are all installed on the opposite wall from the windows, the windows have not experienced any condensation - which may speak to larger proportion of radiant heat than I gave them credit for.
Malcolm and Phillip,
For giggles, I just mentally catalogued the cove placements and three rooms have them aimed inward off of exterior walls. The rest pretty much by default face exterior windows. The electricians had more opinions about where I should put them and since I had no prior experience I deferred to them. The Alpen windows I have rarely experience condensation except in the bathroom after showers. The one window with the insulating shade will get wet along the bottom edge if we drop it all the way down. The insulating effect makes the glass get too cold. The biggest window set in the house is in the living room which does not face a heater and never gets condensation.
If you, (Philip) have indeed planned for Passive Haus levels with commensurate windows, I would not worry about the heater placement. I think my sensitivity to the coves is pretty much directly due to be nearly bald. If you know how to deal with that problem, I am all ears. (and scalp)