Radiant panel + mirror…can i?
I have a 500W radiant panel heater (Aztec Model 2236) nominally 2’x3′, a line voltage thermostat (never used, but old: it was made by Singer), and an idea to mount the radiant panel behind a mirror of the same size above the vanity. Thoughts are that nothing will be in front of the mirror to get in the way of the panel, which actually gets too hot to leave one’s hand in contact with, and the mirror won’t fog. Ever. <G>
I know about the thin-film mats that stick behind a mirror for fog-free mascara application, but they are fairly low wattage affairs.
Can anyone recommend a mastic that will neither harm the mirror nor become thermoplastic? (I can build a metal channel to hold both items, but i’d rather have a frameless look.) I know about the mirror mastics, just never used them to know how they respond to heat. Silicone, which is heat tolerant, tarnishes mirrors.
Second consideration concerns what the effect the silvering has on the radiant panel. I’m assuming that if the two surfaces are in contact, the heat will be conducted through the reflective coating and thence through the glass to radiate to the room. Sound right?
The RP had a bit of texture to it from being painted before. If there is a gap between the RP and the silvering, i’m plumb mystified what happens then. Does the fact the shiny silvering is to the glass side make the point moot? Would painting the back of the mirror black be helpful? Will the energy be reflected back to the RP? The literature said the panel could be painted, but not with aluminum paint, hence my Q.
I plan to experiment closer to the ground before i run wire and install this where it can come crashing down and/or ruin my record of not having any house fires that don’t involve a kitchen appliance, but pointers would be welcome.
Replies
Dunno. High temp adhesive? Maybe. Nothing standard. Not duct tape. Maybe fire caulking?? Not sure if it is good as an adhesive or not. Use a variation of the plastic mirror clips?? Just throwing junk ... er ideas out there.
We have a lot of radiant heat panels and IIRC they run some where around 130-150 degrees.
You might select your adhesive based on a temperature higher than that.
Don't know about the silvering issue.
I've finally found one company in the UK, Marmox, that makes mirrored radiant panels meant for serious heating, so at least i know it's possible. The cost is roughly $700 for a panel of the approximate size and somewhat higher wattage than i'm doing...nice idea i have here! The construction is not clear, but i'll plow ahead with that bit of encouragement. First of all i'll take the panel's temperature, then clamp the mirror to it and see how that affects the thermometer. If that works like i hope, i'll test one of the mirror mastics i've seen for heat strength. If it all goes like clockwork, i'll post the results. If it doesn't, i'll slink off. Thanks to you and Clewless for taking a run at it. I don't post until i think i have a doozy of a question and this one appeared to have stumped the brain trust tonight.
Interesting project.
Have you investigated the expansion and contraction issue yet?
Just thinking the adhesive will have to accomodate some movement between the mirror and panel.
Maybe look at how insulated glass is put together.
Well, that was an excellent point i hadn't considered. I found this table that says, i think, that ordinary glass expands at 69% of the rate that steel does. Since the figures are listed in 10^-6 notation, that seems like a "little bit", but i also haven't a clue at what point distortion would be noticeable. http://hyperphysics.phy-astr.gsu.edu/HBASE/Tables/thexp.htmlIf i find that the heat passes easily through the mirror clamped but not glued to the RP, i'm thinking now that just gluing channels on the back of the mirror that would slide over the panel to secure it would be better anyway, both for thermal expansion co-efficients being different, but also bec if either panel or mirror broke, it would be a nigh impossible to salvage any part of a glued-together assembly.My head's full now, so i'm off to visit my pillow. Thanks for helping me think it over.
I've been in hotels in Europe and Asia that have heat behind the bathroom mirrors. The first time I noticed I thought "dang, I swear I feel heat when I walk by the mirror." It feels great when shaving and the mirrors never fog up. The heat mat was connected through the light switch.
I don't know how they were attached to the wall and mirror. I suggest that you attach the heat mat to the wall with thinset, which is cementious and not sensitive to heat. As for attaching the mirror, I'm at a loss. You can use thinset (think glass tiles) but you want to be sure the silver is not damaged by the thinset.
Why don't you call a mirror company and ask for their advice about an adhesive that that is insensitive to the expected heat and won't damage the silver coating? Maybe there's a barrier paint you could coat on the back of the mirror for extra protection? You also could add a few mirror clips or use molding to attach the mirror in case the adhesive fails. I agree that you want to use some type of adhesive coating to get good heat transfer to the glass.
Use the same approach as with a heat mat and tile on a floor, with consideration given to the silver mirror backing.
Billy
Edited 1/24/2009 10:30 am ET by Billy
Nice to hear a postive, first-hand report of your experience with the de-fogging kind of mirror. The mirror will be right opposite the shower. I'm looking forward to stepping out and thinking "summer".Those heat mats are only about a tenth or less of the wattage of this radiant panel i have and they're more like a very thin film which gets adhered to the back of the mirror with a peel-and-stick adhesive; the mirror holds up the panel, not vice-versa. In any case, this panel has stand-offs to hold it off the wall so attaching it t the wall with thinset isn't an option. I called the best glass company around and they didn't know about the mirror mastic v. the heat either, so they're calling their technical resources on Monday for me. Even if i just use the channels to hold the mirror to the panel, they'll have to stand up to the heat when it's operating at peak demand.
Don't adhere the mirror to the panel at all.
They make wedge shaped channels for hanging heavy mirrors I would try and get the mirror several inches taller than the panel and adhere the wedge at the top behind the mirror with opposing edge mechanically fastened to studs above panel.
This way you just slide the mirror down over the panel and will able to remove when needed.
I believe that the heat transfer will be quite substantial without the direct contact or expansion issues.
ANDYSZ2WHY DO I HAVE TO EXPLAIN TO FRIENDS AND FAMILY THAT BEING A SOLE PROPRIETOR IS A REAL JOB?
REMODELER/PUNCHOUT SPECIALIST
It looks like you're talking about Z-Bar hangers. They screw in, so i'd have to glue wood spacers to the mirror, then screw the Z-bar to the wood. I'm not sure the side view wood be good if it stood off the wall enough to accommodate the panel under it, about 1-1/2".It gave me the idea that if i have to go to something like a mechanical hanger, i could orient the mirror horizontally instead of vertically to get more width for attachments. I was locked into a vertical idea before. Now i'm also considering i could put a shelf under the whole business to help suppport it. Hmmm....thanks for jiggling that idea loose.
If you can glue mirror to wall why not glue z bar to mirror.
And I like the shelf idea even better.
You could also recess the z bar attachment so that the mirror rested against the wall.
ANDYSZ2WHY DO I HAVE TO EXPLAIN TO FRIENDS AND FAMILY THAT BEING A SOLE PROPRIETOR IS A REAL JOB?
REMODELER/PUNCHOUT SPECIALIST
The mirror mastic manufacturers specify minimum coverages per square foot of mirror, so i don't think one strip of Z-bar attached to the mirror would do it. I can bend up a piece of sheet metal to hook over and around the radiant panel while providing a larger gluing surface to the mirror side. Z-bar is rather expensive material for being essentially a French cleat, since i have more time than money.<<recess the z bar attachment so that the mirror rested against the wall>>mmm....not what i'm trying to do. The RP will hold the whole thing out from the wall an inch and a half, so looks will matter.
Ok so put a piece of C -channel on the back of the mirror and let it hook the radiant panel.
Put a shelf on the bottom to carry most of the load.
Then glue a strip of mirror around the sides to hide the edge of the panel and make the mirror appear more substantial.
ANDYSZ2WHY DO I HAVE TO EXPLAIN TO FRIENDS AND FAMILY THAT BEING A SOLE PROPRIETOR IS A REAL JOB?
REMODELER/PUNCHOUT SPECIALIST
Something like that is my next idea, but to hold the mirror intentionally away. There are metal picture framing profiles i could use...
That's a serious radiant panel -- it will be "August" when you step out of the shower!
Enjoy it.
Billy
Thanks! I'm looking forward to inventing this thing!
Don't slink off, dude ... share your failure knowledge w/ us, too. If nothing else for a laugh. OK? : )
High temp silicone gasket in a tube at auto parts store.
larry b
That may be the best suggestion yet. The temp won't hurt it and the silicone will stretch so the glass won't crack.
Billy
<<High temp silicone gasket in a tube at auto parts store>> ...contains acetic acid, which tarnishes the metal.
>><<High temp silicone gasket in a tube at auto parts store>>...contains acetic acid, which tarnishes the metal.<<Not all silicone has has (or I think more accurately generates) acetic acid.Some are what are called Neutral Cure. They are used on electronic assemblies among other things.I have no idea about the auto parts high temp.I am under the impression that the GE TypeII in the home horror stores is neutral cure. There is no small, but they don't document that on their website like they do for the industriall neutral cure.You might experiment with your test mirrors.And look and see what the temp limits are on "ordinary" silicone. I suspect that you panel does not get that hot.But also you probably want to run it off a approriate rated light dimmer. IIRC for the early post it was 500 watts and common dimmers are 600 watt..
William the Geezer, the sequel to Billy the Kid - Shoe
Thanks, i hadn't run across "Neutral Cure" or heard of it, but i'll check it out for future reference. The mastic are asphalt based and seem to go to about 145º. The silicones will go to 450º. They can be used to put new gasket on a woodstove, for example, which is the damn thing i forgot to buy when i drove into town today. *sigh*I went downstairs and sniffed by gasket silicone when a poster recommended it. One smelled of acetic acid and one didn't, so i went to the Permatex website and pulled the info, but it didn't explicitly say it was safe for mirror. If i hadn't had the cracking make me give up adhering it, i would have done some trials with gluing mirror to metal, then heating it up on the stove and seeing if i could pull the two materials apart when they were hot...just never got that far.I really want to thank you for the light dimmer idea! I can USE that, for sure! This Singer line-voltage thermostat doesn't shut completely off, which concerned me. Dimmers i have loads of. (ha ha ha...)
Edited 1/27/2009 10:49 pm by splintergroupie
I wish you luck, but I'm guessing the glass will crack or the mirror will discolor. If the whole thing doesn't catch fire.
I thought you were just being a smartass about the cracking, but i did some experimenting last night with an old piece of 1/4" mirror and that's what happened, but not immediately. This test was done in a horizontal position. I could only get 88º out of the mirror face at 1" from the face (spaced with a cheese grater because my thermometer couldn't go higher than 120º in order to read the actual face). I surmised it was because the face of the radiant panel would warp as it got hot, so mirror and metal weren't in solid contact. I placed a weight on it to flatten them out and measured again, got up to 108º at the face. I was down in the shop when it cracked so i didn't get to witness the event, but the crack was a 1/4" wide on one side, 1/2" on the other - not just a gentle crack, but there was some force driving the pieces apart. I turned the heater off then, but the glass retained heat for a long time, 15 minutes or so, after the surrounding metal was cold to the touch. (The mirror was only large enough to cover about half of the panel.) First pic shows the break. I guess the good news is that the silvering didn't completely prevent the heat from radiating out the front, but this takes care of the silicone issue. For a comparison, i placed slates on the panel, and they achieved similar temps as the panel face itself, more quickly than the mirror did, even though the backs of the slates are rough and not in perfect contact either. So far, my assumptions that the mirroring needs to be in solid contact to prevent reflecting the heat seem to be true, though i hadn't counted on the glass cracking, dang it all. I'd still like to know how they do it in the UK...tempered glass, i'll bet, or maybe they moved on to my next idea, to create a space intentionally between panel and the mirror to hold the mirror heat in a manageable range while siphoning off the rest of the heat via a convecton channel.Or i can just make a really nice towel warmer out of it!
Before you do any more experimenting, get one of these:http://www.q3i.com/thermohawk_series.php
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Yeah, that would do a better job of telling the exact temp than my dollar-store thermometer (actually filched from the hoophouse), but then the folks would start jumping on me for joining Riversong in his "scientism".I'm not sure the exact temp matters when the mirror cracks at whatever temp it gets to. Do you have any ideas for that besides the one i had of mounting the panel and mirror with an airspace-to-be-determined, drawing off some of the heat with convection? Or would you guess - i'm going to start relying on your guesses instead of my schemes - that the glass would crack anyway? I was wondering if there's a heat build-up at the plane of the silvering that just can't be dealt with when the source is that hot... <musing>
Edited 1/25/2009 4:03 pm by splintergroupie
The problem is that you have a lot of differential heating, both from heating the middle hotter than the edges (which creates tension on the edges -- bad for glass) and from heating the slivered layer hotter than the rest of the glass. You first off need to have the glass loosely mounted somehow (so that the mounting doesn't add stress), and you need to somehow heat the outside edges as hot as the rest (or preferably a little hotter). Then you need to regulate the heat so that the differential heating of the slivered surface relative to the bulk glass does not reach a critical level (and I'm not sure how you'd determine the amount of heat it can take without experimenting).And of course there's my prediction that the silvering will fail -- not sure I can do much to help there.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
The Home Re-source store in Missoula had a bunch of used mirror, so i can experiment cheaply with the idea of mounting it in channel in front of the panel. I'll report; you decide. <G>
Keep in mind that you need to avoid any sharp edges impinging on the mirror, in whatever sort of mount you devise.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Roger that.
We use IR guns to check the heat panels in our building. Beats the heck out of dragging a 8' or 10' ladder around to see if the darn things are really working. Our building control system only reads the control current relay. The coputer will say a panel is on even if it is smoked and the breaker is tripped.
"ThermoHAWK™ 400U Features• +/- 1° from 10°-100°F
• +/- 2.5% from 100°-428°F
• Sleek Compact Design
• Easy To Use
• Digital Display
• Includes UV Light"I wonder what the purpose of the UV light is for?.
William the Geezer, the sequel to Billy the Kid - Shoe
Got me.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
That brings up an issue ... if your 'glue' is not forgiving (i.e. plyable rather than 'rigid'/stiff) the difference of the coeficient of expansion between the metal and the glass may always create stress that won't be tolerated by your mirror.
One other thing to consider is the thermostat cycle. Once the bathroom is warm (hopefully before you go to use it) the heat will turn off. Depending on the thermal mass of the mirror/heat panel, the mirror might not still be warm by the time you want to shower and it might fog up. 500W is a lot of heat.
The idea is really creative but I wonder if you just embed some warmwire (~100W) in the drywall behind the mirror and attach the mirror normally whether the anti fog would be more effective. Just put the control on a timer and by the time your shower is done, the mirror is warm and fog free. Possibly cheaper than the salvage operation. If my master mirror has not been set yet I might try it (but it was supposed to be done last week)...
I don't know what kind of glue my glass guy is using to glue my master mirror to the drywall (I'll ask this weekend) but glass glues must exist. I'd bond some wood strips to the mirror (epoxy?) and mechanically attach the hot panel to the wood. The small air gap will help lower thermal shock and differential expansion stresses on the mirror. If the hot panel must touch the mirror, I'd use a thin isolation sheet (neoprene?) to separate them.
Cool idea! Eric
I wasn't trying to get a fog-free mirror as my prime agendum, but it was a nice side benefit of a working radiant heating mirror. If you google mirror + de-fogger, you'll see all kinds of differently sized heating mats for attaching directly behind you mirror. The mat itself comes with a sticky side for rolling onto the mirror back. It only needs to raise the heat of the mirror a very few degrees about the surrounding temp to make the mirror fog-free, and that only costs you about 15-45 watts, depending on size.
The table i linked showed that the metal and glass aren't that different in their thermal distortion, but i think Dan hit it on the money when he talked about tension within the mirror itself from the hot center to the relatively cooler edges; likely there was more tension within the mirror than between the two materials. It occurred to me the mirror broke rather cleanly in halves, too. I was reminded about concrete: when it doesn't have control cracks as it cures and shrinks...it makes its own.
Edited 1/27/2009 10:51 pm by splintergroupie
I have used a shellac barrier for a similar situation. Shellac was used for decades to bond glass/metal in a high-temp environment: i.e. light bulb glass vacuum chamber to the metal base. It will bond to most substrates, is a little flexible for allowing lateral movement, and is heat resistant. Let me know if you would like some more info. Good luck.
Are you one of Frenchy's friends?
Sorry, had to do it
Ouch!!! Ha!
I just googled about glass, metal, and shellac and it was really interesting, except when i substituted "mirror" for "glass", the trail went dry. The thing is, once the mirror is silvered and the back painted to protect the silvering, one of the materials is no longer glass. The shellac adhesives also require UV light to cure, or so i read.That was a good idea, though, and i learned something i might have a use for later. Who's going to be the first to tell Frenchy, who is already permanently bonding to shellac? <G>
What I was thinking, was to coat the back of the mirror with shellac to protect the silvering, and then use a high-temp, higher viscous adhesive, knowing that it wouldn't effect the silvering but would still bond. Basically the shellac would be a protective barrier between the silvering and a strong adhesive. I would coat the back of the mirror and let it cure a good 72 hours prior to adhering...
The mirrors are already painted with paint and/or copper to protect the silvering, but the shellac probably wouldn't hurt as further chemical insulation.
Hide Glue. The real deal from scratch. It's fairly flexible and is or was sold in a grade called "Glass Chipping". I.E. it stuck good nuf to chip the glass when prised off.
Maybe.
BTW, Cheeze Graters are done when they reach an internal temp of 100 degreeeeeeezz.Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
They kill Prophets, for Profits.
The glue chip is made because hide glue shrinks as it dries; i'd get glue chip no matter what i wanted, lol. Sometimes you see mirror that's been silvered AFTER it's glue-chipped...very pretty. OTOH, steam and heat are used to dissolve it, eh? Bathroom?Aside: the size of the chip is determined by the solution strength of the hide glue. There's a glue-chip glass called "Tsunami" that has a really large, deep chip to it that i used in my jewelry box tops a bunch, esp since that was a whole lot easier than raising a wood panel.
Edited 1/25/2009 4:12 pm by splintergroupie
Whelp, dats all I gots!
G'luck.
'first we do the possible, then we work on the impossible' Used to be my mantra..LOLSpheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
They kill Prophets, for Profits.
> Hide Glue. The real deal from scratch.If I'm not mistaken it softens with heat.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Im just a blindman with a pinata stick today, duck.Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
They kill Prophets, for Profits.
I mount mirrors for people using these clips from CR Lawrence CO.
View Image
http://www.crlaurence.com/ProductPages/6/64114BV_48848.html?Origin=
A beveled mirror looks very nice mounted frameless on a 3/4" sheet of plywood an inch narrower than the mirror all around; makes it look like the mirror is "floating" in front of the wall. To make room for clearance from your radiant panel you would probably fur out a bit.
These little clips can each hold 50 lb, so two pair would be plenty strong enough for your mirror, yet the visible part is only about the size of half a dime.
Mount the bottom ones with screws through the sliding clip and its mounting bracket, the top ones you mount the bracket and slide the clip down over the top edge of the mirror to hold it firm; easy to remove too.
Thanks for posting. I've seen those clips, but wondered if they really could take the load, so it's good to hear the voice of experience. The more i think about mounting the RP above the vanity, then siphoning the majority of the heat off convectively, the less sense it makes. I'm leaning toward putting the radiant panel on the wall behind the towels now. Warm towels...yum! And i can mount the mirror any way i chose. I like the "floating mirror" idea, too.
What's the emissivity of a mirror? 3%? The whole exercise is suspect.
OB
I'm not sure what the emissivity of the mirror is, but i don't think that's the problem.
If the mirror was painted black it would work much better as a radiator. And if it worked better as a radiator the glue wouldn't get as hot.
Why not do a heat-a-lator setup and let the air flow in behind the mirror and out the top. The mirror would still be warm and the energy used would actually heat the room.
OB
I can rather quickly set up test conditions when i get to that stage and rather a good idea to do so. I guess the choice is between a de-fogged mirror and warm towels now, lol...What i expect - not that my expectations are worth much at this point - is that siphoning off the heat with convection from a heater mounted in the upper half of the room (above the vanity) would give me a warm ceiling and a clear mirror. If it's located lower on the wall as a radiant source, my bum would be toasty (it's also close to the ground) as well as the towels.OTOH, i do have three of these 500W panels...but then i'd have to run a separate circuit, so scratch that.
My glass guy uses mirror mastic to glue the mirrors. CR Lawrence?
He says there are tons of specifically designed mirror defoggers. He wouldn't put 500W behind a mirror.
We put in new halogen lights. They are 3 lights of 100W each per bar, two bars in the bathroom (600W total). This heats the bathroom very nicely and seems to prevent fogging. The steam load hasn't been really tested as just the tub is working - the shower doors are still on order. The only real problem with the lights is that my wife can see all her wrinkles - a dimmer is going in.
I am very interested in your panel as a towel warmer. I'd put a timer on the panel, crank the timer before my shower and have a nice warm towel to dry with. Where did you find these panels?...
Eric
With 600W of halogen light in your bathroom, i'd expect you'd need sunscreen in there! I have a groovy, halogen, ceiling light fixture in the middle of the room that uses 250W on full power, which also adds quite a lot of heat...not always welcome. I've considered changing it for an energy-efficient fluorescent, but i love the thing for its looks and dimmability. I gave myself a remote-control dimmer for Christmas and it's such a joy to be able to read in the tub, then dim the lights for a luxurious finale to the whole bath experience. Yum!I'm going to use an outlet thermostat made by Lux (WIN100 model) to plug in the panel(s). I liked Bill H's idea of a dimmer for the panels because it's cheap and sleek, but realized it would provide a constant heat output at whatever level instead of being thermostatically controlled. The LUX outlet thermostats are well reviewed and also have an "off" setting, which i desired. Also programmable so one could have a pre-warmed room and towel after a morning shower.The three panels came to me as booty from a failed marriage among Mormons who split, who'd followed the Mormon teaching of keeping a year's provisions at hand. I was called to see if i'd come remove 2-1/2 tons of their stored food from the house they needed to sell to settle. They'd done a pretty poor job of building their faux-stone McMansion, too, and i gathered the panels had been expected to heat a space much too large for them. All sorts of stuff was getting tossed from tools to commercial coffee grinders, so it turned out pretty well for me, but the sheriff was repeatedly involved in their lives before they went their separated ways.
Hi, I discovered this thread when searching to see if a radiator can be positioned behind a mirror.
It's some time since 2009. @splintergroupie.. did you develop your idea so it worked?
I have an idea to fit a radiator mid height on a wall above a basin and washing machine unit in a spare bathroom, that is doubling as a laundry room.
The plan is to be able to hang washing to dry on rails above the unit, above and in front of the mirror
When no washing is hanging, it can return to guest bathroom status.
My thought is to attach the mirror in front of the radiator. (Not stick it as you've suggested)
There could even be a gap between the back of the mirror and radiator front, as I thought to frame it out.
Possibly could make it oil filled/electric, with the thermo valve/timer located at a distance in the hallway.
Did you make yours? Did you need to use a tempered glass mirror?
Any other advice you've gleaned in the past 15 years?
While I think she is still alive, she has not posted here in several years.
Google her screen name and you might get lucky to find the link to her current “residence”.
Here you go.
Another fine group of knowledge givers!
https://forums.delphiforums.com/Breaktime_3/messages/?start=Start+Reading+%3E%3E