Flex Watt Mfg says NO to foil/aluminum tape

Originally Posted by btbutler

No you are fine, don't worry . If you arent touching the conductor of the heat tape with the foil tape, it would be next to impossible for the heat to transfer in the foil tape, except for the radiated heat that comes off from the tape, which wouldnt be much. The main type of heat that you are trying to get out of heat tape is conductive heat, which is why you have the heat tape touching the tubs in a rack system. If the foil tape is not directly touching the conductors on the heat tape, there will be little to no conductive heat transfer, which would mean that you couldn't create hot spots. Is some of the foil tape going to be affected by the radiated heat off of the tape, yes. Is it going to be in temperature spikes of 10+ degrees, no. You may have a spike of somewhere around a couple of degrees. If you touch the plastic edges of flex watt, you will notice it doesnt get anywhere near as warm as the center conductors. This is because metal is an excellent conductor of heat, and plastic is relatively poor at conducting heat. Hence why we insulate houses with fiber glass and styrafoam. Generally speaking, if it is a poor electrical conductor, it is a poor heat conductor. Vice versa. Good heat conductor, good electrical conductor.

This. Aluminum tape is conductive, so if putting aluminum tape on the heat tape shocks you, wouldn't the heat tape by itself shock you too?

Originally Posted by Focal

The fact that heat rises and often takes a path of least resistance, it rises just fine.

Incorrect. Hot air rises. Heat moves from areas of higher temperature to areas of lower temperature.

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The main problems with heat tape are (1) what others have already mentioned about covering the conductive ends after cutting it and (2) to be sure that the tape can "breathe"--i.e., it isn't set up in a way that causes excessive heat buildup (the tape can't dissipate excess heat).

For example, I have metal racks with heat tape completely covered in foil tape. Foil tape is a conductor, which is the reason why it's good to use on heat tape. You want to heat the bin, not just the tape! (Isn't duct tape more of an insulator, by the way?) The metal shelves are not solid, and there's a gap between the bottom of one shelf and the lid of the tub underneath. This allows several pathways (tub, shelf, air) for any excess heat to dissipate.

EDIT: The reason I put aluminum tape on top of the heat tape is to decrease the chance of damaging the Flexwatt itself (damaged heat tape is a fire hazard). If any damage occurs, it will happen to the aluminum tape first, making damage easy to see and easy to repair.

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Radiant heat panels (and ceramic heat emitters) emit infrared light (IR). This is different from heat tape, which is used to transfer heat (kinetic energy of the molecules) from one object to another through conduction. (Though, the heat tape--well, everything in the setup, including you!--also emits IR.) Brendan probably said it better, though.

Krystal, I have to disagree. Metal Duct tape works by keeping heat/cold from passing through the tape and reflects heat/cold away with the reflective side. So you are actually causing more heat build up by completely covering the tape. As to the breathing, you said Heat moves from areas of higher temperature to areas of lower temperature, so if the tub is cooler the the surroundings this is where the heat will transfer to. You shouldn't get heat "buildup" as your thermo should regulate it that it stays within the target temp.

Originally Posted by R. Eventide

This. Aluminum tape is conductive, so if putting aluminum tape on the heat tape shocks you, wouldn't the heat tape by itself shock you too?



Incorrect. Hot air rises. Heat moves from areas of higher temperature to areas of lower temperature.

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The main problems with heat tape are (1) what others have already mentioned about covering the conductive ends after cutting it and (2) to be sure that the tape can "breathe"--i.e., it isn't set up in a way that causes excessive heat buildup (the tape can't dissipate excess heat).

For example, I have metal racks with heat tape completely covered in foil tape. Foil tape is a conductor, which is the reason why it's good to use on heat tape. You want to heat the bin, not just the tape! (Isn't duct tape more of an insulator, by the way?) The metal shelves are not solid, and there's a gap between the bottom of one shelf and the lid of the tub underneath. This allows several pathways (tub, shelf, air) for any excess heat to dissipate.

EDIT: The reason I put aluminum tape on top of the heat tape is to decrease the chance of damaging the Flexwatt itself (damaged heat tape is a fire hazard). If any damage occurs, it will happen to the aluminum tape first, making damage easy to see and easy to repair.

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Radiant heat panels (and ceramic heat emitters) emit infrared light (IR). This is different from heat tape, which is used to transfer heat (kinetic energy of the molecules) from one object to another through conduction. (Though, the heat tape--well, everything in the setup, including you!--also emits IR.) Brendan probably said it better, though.

Yes exactly the aluminum tape is a conductor. Not an insulator. The duct tape is a non-metal synthetic material, therefore it is an insulator. Duct tape would actually create a hot spot, as well as be a fire hazard, and also keep a lot of the heat from getting to your tubs. That goes for the kevlar as well, as kevlar is also a synthetic non metal material. You have to think of physics in this case, as you are working with heat and electricity. If you have no concept of physics, in this case you would be working blindly. Not trying to be rude or anything, but it is the truth. If you just use the duct tape to hold the plastic edges, that is fine, but otherwise it is potentially dangerous and could cause a fire if it covers the black heating elements when a thermostat fails. Aluminum tape cannot be set on fire (at least by standards of just being plugged into the wall, and also doesnt create hot spots, reflect heat, or cause any of the previously mentioned issues that duct tape or any non conductive material tape. Just make sure you dont

Brendan, Here's the number for The flex watt mfg (800 922-9276) they are in MA.
Ask for Jim he's one of the teck guys there. You seem to be a Physics guru of sorts so it would be a good conversation. Jim suggested using duct tape (top and bottom), and strongly advises against using aluminum tape at all and I think he said using aluminum tape WOULD cause hot spots. If it's not too much trouble I'd like to see a post here, and I'm sure others would also, on the outcome of your conversation.

If I understand your comment correctly using an under laying base of rigid blue board insulation would trap heat and be dangerous. Jim recommended it under the tape to help direct heat upwards. I was planning to do this on my next build, as well as use a underlying layer of heat resistant poly tape on top of it.

Originally Posted by MrBig

Krystal, I have to disagree. Metal Duct tape works by keeping heat/cold from passing through the tape and reflects heat/cold away with the reflective side. So you are actually causing more heat build up by completely covering the tape. As to the breathing, you said Heat moves from areas of higher temperature to areas of lower temperature, so if the tub is cooler the the surroundings this is where the heat will transfer to. You shouldn't get heat "buildup" as your thermo should regulate it that it stays within the target temp.

"Metal duct tape"? I can't say I've ever heard of that. Doesn't mean it doesn't exist, of course, but I was not referring to any type of metal duct tape in my post.

If metal duct tape works by keeping heat/cold from passing through, then it's an insulator. (Aluminum tape is metallic--it is a conductor--and it is most definitely not a type of duct tape.) Shiny material reflecting light (it doesn't reflect "heat," in the colloquial use of the term) has pretty much nothing to do with what we're talking about here. Shiny surfaces reflect both visible light and IR, but that has nothing to do with a heat source underneath it. Actually, dark material radiates heat (IR) faster than lighter material. (EDIT: Nifty useless facts! This is why telescope domes are white or shiny. When observing, we want the air around the telescope to be as still as possible so as not to distort our images. A dark dome would radiate the heat it built up during the day like crazy, causing a crapton of turbulence just beyond the telescope itself! Not good! This is also why we temperature-regulate large telescope mirrors as well: we want the temp of the mirror to be the same as the temp of the air directly above it. End nifty useless facts!)

Whether the heat from the tape transfers more quickly to the tub or the shelf depends on what material the tub and shelf are made of. If the shelf is made of a material that conducts heat better than the tub, then more of the heat will be lost to the shelf. Though, if you're using an enclosed rack unit with the heat in the back, this will help heat up both that shelf and the one below it (since the shelf is warming), so technically, you're not "losing" or wasting the heat.

Thermostats can only regulate the temperature where the probe is placed. If the probe is placed at one end of a span of heat tape, one can still get hot spots. The heat tape is basically a big resistor, so a heat buildup at one end of the tape will not spread equally throughout the length of the tape. That hotter section will remain hot, unbeknownst to the probe at the other end.

What was the concern with a vertical installation? I currently use 11" heat tape in a back heat configuration (stapled by the edges to osb). I want to replace the tape and am trying to think of a material to attach it to and possibly sandwich it between that would be:

1. non electrically conductive
2. non flamable
3. good heat conductor
4. good heat sink
5. rigid, durable, and portable

I have lots (like 9 inches) of insulation behind the back of the shelves and about 35 square feet to cover. The heat tape will not be under all the area but I would like a material that would spread the heat out and have some capacity to store heat in case of a power outage. I also need to be able to take the heat system out and move it without damage as I periodically break this snake room down and move it.

Was thinking of maybe sandwiching the heat tape between two layers of melamine even though it's relatively expensive, very heavy, and I'm thinking not entirely fireproof in spite of all the nitrogen. Is there some sort of large format (at least 4' X 2') tile or tile backer board product that would also conduct and store heat well and not be totally fragile (I've pretty much excluded glass for that reason)?

You can only enhance the chances of creating hotspots by completely covering the heat tape in metallic duct tape. This is sold for the purpose of sealing joints in metal ductwork, hence me calling it metal duct tape.

Originally Posted by CornNut

What was the concern with a vertical installation?

I don't know. I was wondering about that too. Electricity/resistance doesn't care what orientation it's in....

As for the rest, I don't know what materials to use off the top of my head. You should be able to find heat capacity, conductance, etc. for most synthetic material online, I would think. It'll probably just take some research on different kinds of material to see what would be best. Maybe make up a spreadsheet with properties and pros/cons of different things--should make it easier to compare.

Originally Posted by MrBig

You can only enhance the chances of creating hotspots by completely covering the heat tape in metallic duct tape. This is sold for the purpose of sealing joints in metal ductwork, hence me calling it metal duct tape.

Okay, I will ask again: What is this metallic duct tape? You say it's used for metal ductwork, but this tells me absolutely nothing about the tape itself. Is it actually metal or is it just shiny? What else is it made of? What kind of ductwork is it for? From my limited experience with ductwork, most ductwork I've seen is for transporting air, so there's no reason why tape for sealing ductwork joints would need to actually be made of metal (unless there's no other way to make it blend in with the ductwork itself).

Also, I repeat: What does metallic duct tape have to do with this thread? No one here has mentioned using metallic duct tape, as far as I remember. We're talking about normal duct tape, Al tape, and some type of kevlar tape.

EDIT: Wait, are you referring to Al tape as "metal duct tape," for some strange reason?

I have seen a "metallic" duct tape and the standard grey duct tape in hardware stores. Both made by the Duck tape mfg. I never bought the "metallic" duct tape, and so I can't say it's really metallic like the aluminum foil tape or not. It does exist though.

It is the only tape allowed by universal building code, to be used to seal duct work from leaks. It is reinforced with fibers like grey duct tape. Like alluminum tape it does have a slight insulating factor, as well as being an electrical conductor. Alluminum tape is simply the cheap version of the tape I'm referring to. Being a certified HVAC/R contractor, I'm well aware of how heat transfers, and the materials we are discussing. That being said, I used metallic tape over just the clear edges of flexwatt, I have since replaced it with the kevlar because of profile, ease of sliding, and durability. Given that I only cover a 1/4" of the clear plastic on the ends, I am not in anyway concerned about Kevlar being an insulator. I also cover all cut ends with electrical tape to avoid any issues.

As to why you need metal tape for ductwork, there are numerous reasons. First is that you loose significant amount of airflow and velocity and efficeincy when you don't seal joints. Second universal building code requires the use of it. Third, metal tape does not dry out and deteriorate at anywhere near the rate of grey or alluminum duct tape. I do not know the exact metals used to make said tape, only that it is significantly stronger then either of the other options. Blending in is of no concern when making or sealing ductwork, keeping hot/cool air in the ductwork until it reaches the desired location is the one and only reason for using tape or mastic to seal joints. It is used to seal all types of duct, from sheet metal, to duct board, to spiral. Hope this answers any questions you have, and again i reccommend that you don't cover your complete heating surface as you are only asking for trouble in doing so with no real advantage.