This is a diy project. If you choose to build one, you build it at your own risk. I make absolutely no guarantees and assume absolutely no liability for your project. As always please use common safety practices and common sense!
The heating parts and the PVC pipe will be hot enough to cause nasty burns on contact so be sure to wear good leather gloves.
There are a few commercially available products but they are quite expensive. I have used both the heating box type and the blanket type and a big problem with these is that there is essentially no temperature regulation. If you're not constantly checking your PVC as it is heating, the PVC will overheat, become much too soft, and even burn and bubble.
My goal was to come up with a heating solution that has temperature regulation, allowing one to 'set it and forget it' without fear of overheating.
I also wanted something compact, portable and safe.
I've been thinking about this for a year or so now and have fiddled around with several possible solutions. I have some ideas for an inexpensive heating blanket so stay tuned.
I've finally come up with something I like and it works great.
What you will need:
All process are approximate
Small tool box $10.00
Piece of 4" round sheet metal duct $5.00
12x12 heating mat for a 3D printer $25.00
4" ID Rigid fiberglass pipe insulation $10.00
120v PID with thermocouple $10.00
Plumbers heat shield $15.00
The duct, tool box, plumbers heat shield, and pipe insulation are available at the blue and orange big box stores. The PID and 300mmX300mm heating mat (made for 3D printers) can be found on eBay.
You can get a PID with an electronic relay and that's fine. The pad I got draws 500 watts at 120 volts and that's just over 4 amps. The relay in the PID is rated at 6 amps so it should hold up ok, but a 30 amp SCR wouldn't hurt.
The heating mat has adhesive on one side.
Make sure that the thermocouple that is integral with the heat mat will work with your PID. Mine did not, so I placed a K type thermocouple under the heating mat before I stuck it to the stove pipe.
I also painted the inside of the stove pipe flat black for better heat radiation.
Stick the mat to the stove pipe, don't snap the stove pipe closed, leave it open.
I used a small plastic tool box, but you can use a metal one if you wish. The insulation I used protects my tool box so it doesn't melt.
Place the stove pipe into the rigid fiberglass pipe insulation and trim the ends as necessary to get it to fit into your box.
I also placed some flat rigid insulating 1/4 inch thick panels (I had some of this kicking around, you could use some thin cement tile backing board) on both ends of the pipe inside the box to isolate the heat from the plastic.
You can also put some regular fiberglass insulation in the box to fill in voids.
Figure out where the center of the pipe is and drill 3" holes in each end of the tool box.
I also cut a plumbers heat shield in half and put 1/2 on each end of the pipe inside the box and cut an "X" into each end so you can slide the PVC pipe in and the ends will be somewhat sealed so the heat doesn't escape.
I cut out a square hole in the top of the tool box to mount the PID neatly.
Wire the thermocouple to the PID. wire an extension cord, hot to the PID relay contact and PID line terminal, the neutral to one of the 120v leads from the heat shield and to the PID neutral terminal. Attach the other 120v lead from the heat mat to the other relay terminal on the PID. That's all for wiring. You can add a switch if you like.
I've tried 1/2", 3/4" 1", and 1-1/2" PVC with great results.
Set the PID to 220 degrees Fahrenheit (or 105 degrees Celsius) as a starting point and have fun.
The reason I left the stove pipe open is so that the heating pipe can be placed over an existing PVC pipe so that it can be bent in place I'd necessary. You would need to insulate the setup somehow.
Please let me know if you build one and if you have any suggestions for improvements.
Ted
