What is the efficiency of gas powered infrared radiant heat?
My project: Climate zone 6A Hortonville, WI 54944 Energy source: electric or propane, no natural gas available
An earlier post about heating garage brought up the possibility of gas powered infrared radiant. I’m familiar with these devices, but I literally can’t find any information from the manufacturers regarding their efficiency. They all claim to be “very efficient” for various reasons, but I can’t find hard data.
Are they rated by a percent like house furnaces? I.E. Are they in the range of 80% efficient ceiling hung unit heaters?
In my particular case, I’m looking to heat my workshop. Aesthetics aren’t an issue. I was leaning toward using a Modine Effinity 93 ceiling hung unit heater. This is a condensing, pvc direct vent style ceiling hung unit. To my knowledge, Modine is the only company offering a heater like this. I like the idea that I don’t need a roof penetration with this unit, since it can be side wall vented with 3″ pvc. I also like that it’s substantially more efficient than the 80% standard vent units.
My building particulars are as follows: R-18 insulation on perimeter frost walls, R-10 slab insulation, approx R-36 clear wall. The ceiling has some areas that will be dense packed to approx R-41, while the attic areas will be R-60. (The shop has bonus room space above)
The wall assembly from exterior to interior is as follows:
1. Ribbed steel siding (I used a ton of cap staples over asphalt felt to give some degree of rain screen)
2. 15# felt as the WRB
3. 1/2″ plywood sheathing (all joints taped with ZIP tape)
4. 1.8# density blown fiberglass (2×8 walls, framing 24″ o.c.), R-20 insulated headers
5. 2″ type 1 EPS (taped joints, bottom sealed to floor) –This foam layer is my interior air barrier and vapor retarder
6. 3/4″ wood strapping
7. 1/2″ ply interior wall finish
I like the idea of using radiant heat since the concrete will be nice and toasty, but I don’t know what I would potentially be giving up in efficiency. My intention is to keep the interior heat level at about 45 degrees unless I’m working, and then it will be turned about to the 62-65 range. I ruled out in floor radiant since I didn’t want a complex heating system and I want the flexibility to turn up and down the heat as needed without a long lag time.
Can someone give me a general idea about the efficiency of gas radiant?
Also, how long do they take to heat up the space or make it feel comfortable?
Also, are they okay to use in an area that is dusty, i.e. woodshop?
Are they easily controlled by thermostats?
Thanks.
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Replies
Rick,
The information you seek is on the Modine web site.
The manufacturer claims, "The Effinity93 (model PTC) from Modine is the most efficient gas-fired unit heater in North America. With ten models available - from 55,000 to 310,000 BTU/hr - all operating at 93% efficiency..."
The only question is what lab test was used to determine this efficiency level -- whether it was a standard AFUE test, or some less stringent protocol. I wouldn't sweat the details too much, however -- especially for a garage heater. It's a condensing appliance, so it's probably about as efficient as your are going to get if you want a vented gas appliance for your garage.
Rick, I love love love this type of garage heat. My auto dealer's repair garage has it, nice, the cashiers at Home Depot by the big forklift door have it... like being in Key West for a winter visit... oh so nice. And you feel the heat fast... if the garage doors open and close often.
I think you will love it. Let us know. And you may not need as high a temperature as you posted. The heater is heating you directly.... radiantly.
What's it going to cost you? I am about to build a workspace myself, and will have natural gas from the street by next year.
I just looked at the link Martin posted... it's a blower.. not the long tube radiant type I was posting about that are radiant heaters.... I need to look more... my bad.
This style I like... not necessarily this site for purchase...
http://www.h-mac.com/infrasave-itb-60.html?gdftrk=gdfV26629_a_7c205_a_7c490_a_7cInfraSave_d_ITB_d_60&gclid=CNay_czqlcICFe7m7Aodtx4A2Q
Rick, you may like a different style and it may be a better fit for you...
Martin, thanks but you misunderstood what I was asking. I knew the efficiency of the Modine unit is 93%, which is why I thought it was a good option for a shop style heater. I ruled out in floor radiant for many reasons, and I can't use minisplits due to the dust. I had never thought to investigate the tube-type radiant infrared heaters until it was mentioned on a recent post.
I was looking for comparisons between the Modine and infrared gas radiant heaters. The infrared heaters are the long tubes or large "Mr. Heater" type fixtures. Dana seemed to think these were a good option for a garage, so I'm curious about how they would work for a larger building.
I've done some demolitions of older commercial buildings that had tube radiant heaters (ceiling mount) but I haven't seen them used on anything recently. That makes me wonder about their efficiency.
http://www.rezspec.com/files/MC-IR_vB2.pdf
See link for a Reznor infrared tube heater. Reznor and the other companies selling these heaters only specify the energy input. It's interesting that they allow certain models to be unvented, but only if the internal volume of the room is greater than 214 cf per 100 btu/hr of heaters installed. For most buildings this would seem an impossible feat, and I wouldn't want the moisture of an unvented heater anways.
Found on Wikipedia:
"The efficiency of an infrared heater is a rating of the total energy consumed by the heater compared to the amount of infrared energy generated. While there will always be some amount of convective heat generated through the process, any introduction of air motion across the heater will reduce its infrared conversion efficiency. With new untarnished reflectors, radiant tubes have a Downward Radiant Efficiency of about 60%. [The other 40% comprises unrecoverable upwards radiant + convective losses, and, flue losses.]"
Interesting, but still not very specific. In my circumstances, the unrecoverable upwards radiant would be scavenged by the room in attic area above. The floor between the shop and room above will be insulated so I can zone heat, but perhaps the heat reflected upward would be useful.
AJ, it is a beautiful heat to be standing near one of those tubes. I also like the fact that you don't need electricity to operate them, and they are nearly silent while running. I'm still trying to find some quantifiable efficiency numbers.
How can you properly size a unit if you don't know the output?
I would presume that with a well insulated concrete floor, these units will provide a warmer floor than a properly sized in floor radiant?
Rick,
The efficiency of all unvented heaters is the same. It's 100%. Some of that is radiant heat, but the other types of heat (convection and conduction) are still in your garage (assuming you are talking about an unvented heater).
Martin, most of the tube radiant is vented. They do allow unvented installation, but only if the requirements I outlined above are met. In your experience with unvented heaters, wouldn't this lead to excessive moisture and condensation within the building if it's not exiting the flue?
I guess for now I'm figuring the gas burning efficiency to be 80%....This would account for the flue losses. Any remaining losses wouldn't be a net negative if those losses are to convection and conduction. I'm still interested about the in-use efficiency. If you warm the objects, and the objects (cars, concrete, cast iron machines, etc) heat up fast and continue to radiate heat once they are heated, maybe heat can be turned off sooner.
I've read anecdotal reports about people being comfortable with a lower thermostat setting using radiant heat, but I don't know if it's marketing gimmickry or not.
You will buy a vented unit.
Cold space quick heat go with tube style 40k for me with 20' tube.
If no garage door use and only mild turn down of temp then go with blower.
The efficiency is not the issue. IMO.
If you paint radiant floor would be nice.... Explosian proof set up and no dust circulator.
AJ, do you know what the heat throw of a radiant tube is? Is it cone shaped based on the angle of the specular reflector and your ceiling height?
For instance, if my heated area is 48' x 40' is one 40' tube down the center of the area sufficient? Or would I need two of them. Radiant heat is kind of baffling to me as to how it fills the room.
The workshop area I'm heating has no garage doors. Does that change your advice? Windows are U.19 triple glazed vinyl.
Nice rather large space. Ceiling height?
Two blowers at opposite corners 40-50 k since you have no garage doors.
Or at least two tubes. Select areas for warmth and or less air movement.
What is the space used for?
Both set ups heat quick. The radiant will heat the floor up which I like and I don't like listening to a blower. And I do finish work and garage doors to open and close too often.
Also Just wondering if Hortonviller's here a who?
Rick, not sure if you have your answer on the radiant tube heater. If not, I can tell you I have a 40 x 60 and had a heat loss calculation completed by the manufacturer rep. The suggested setup was a single 30' tube, 80k BTU. So, depending on your configuration, one may be sufficient. I saw a diagram regarding one straight tube vs. a u-shaped tube, the heat pattern is quite a bit different since the tube cools the farther down it goes. So if you have a need for warmth along the whole length, you might need to consider a different configuration. If you simply want to have a fairly warm shop to play in, a straight run will probably work. Without garage doors, you surely save heat loss substantially.
Hope this helps with your planning. This community board has been a great help to me so far!