I recently bought an IR radiant heating panel to cut down on heating cost. The idea is that it heats surfaces instead of the air, so if placed close to people, the overall air temperature can be kept lower than would be otherwise pleasant. It feels like sitting next to a fireplace, although much weaker. Considering the goal, the only reasonable place to put it was the windowsill.
This location is a problem though, because the panel radiates backward too, and glass is not a great IR reflector. I needed something that would keep the heat inside, so I’m warming up the room and not the outside world. This is when I remembered the reflective sheets that I’ve seen stuck to the wall behind radiators in some places.
This IR reflective foil doesn’t cost much and it’s easy to buy in small sizes (eg. for a single radiator). This is perfect, but I want to be able to easily remove it when I’m not using the heater in the simmer, so sticking it directly onto the window was a no-go. I needed something to keep in a flat shape. The first attempt was done by sticking it to a large piece of cardboard. This worked well, but just until it got a few hours of actual use. I discovered that cardboards tends to warp when heated. Oh well.
The proper solution
I bought some 3mm thick HDF (High Density Fiberboard) cut to size, which I’m hoping will not warp that much. It’s quite cheap.
Now, I’m going to be covering a sizeable chunk of a sunny, south facing window. It would be much better to capture this energy instead of reflecting sunlight back outside off of a light surface. I decided to paint the back of the HDF board black. Additionally, to allow this heat to be circulated into the room instead of being stuck directly against the windowpane, I put a spacer in each corner of the reflector. The perfect material for these turned out to be a block of cork that’s originally meant to be a sandpaper holder. It can be cut reasonably well with a big, serrated knife. I attached the spacer legs with simple wood screws.
The reflective side
The reflective foil was not self adhesive, so I used some double sided tape I had lying about, which I used to stick rubber feet back onto a laptop. Plain tape was coming loose when the laptop heated up, so I got some heat resistant tape which also came in handy for this project.
Final product, after black paint and reflective foil affixed:
Holding it place
A way of holding the board in place would be just sticking it onto the window glass with double sided tape. I wanted something more elegant though, so it can be repeatedly removed and put back. Solution? Magnets!
I’ve found a online store with magnets that sells pairs of self adhesive magnets that can make a “magnetic clasp”.
Fails and Goofs
- To keep the panel sides smooth, I wrapped the foil around the edges of the board. I wanted this extra to be short, so it doesn’t cover the black area, but I cut it too short for the double-sided tape to hold onto it. Fixed with CA glue.
- The cork legs are ugly, especially with the poor paint job – i just wrapped some silver tape around them and now it blends in much better.
- the magnets were quite weak and the was adhesive not holding – I replaced the window-side magnets with bigger ones, using mirror mounting tape. This seems to hold well so far.