11:56 am. It is 36 outside, very sunny with a slight breeze. I installed the heatbox yesterday. It was later in the day when it was done, so it did not have a chance to build up much heat as I was running out of daylight. In my collection of junk I had a bathroom vent fan. I decided to hook that up to the input hose the help force some of the hot air back into the room. I would not be able to see if that would work until today.
Using an electric fan probably kills the idea on saving anything a little but I’m sure it is not as bad as using fuel oil. The idea was to sort of offset the cold in the shop area, I never really expected it to be balmy back there. I was not happy with the flow from the small bathroom vent fan so I hooked up something with more guts. This made a difference but I was noticing a drop in temperature. I kind of expected that as I would be pumping cold room air into the box but it seemed to keep dropping. Since the input was directly in line with the upper output, I thought that maybe I was just forcing too much air directly through the piping in the center. I made a small deflector to throw the air to the sides rather than let it shoot straight up – this helped a lot. The average heat coming out of the output vent is now around 80 degrees. I’m guessing it would still take all day to warm it up back there and then… you run out of day. Perhaps for the size of this box, heating a smaller area makes more sense.
Update – Friday, Dec. 2. Today was a very clear and sunny day. Outside high eventually reached 38 this afternoon. When I came in this morning, the outside temp was 21. I turned the fan on around 8:20. By 8:30 or so, the air from inside the shop had cooled off anything that had built up in the box and from that point the output temperature continued to rise. By 9:30 it was around 70, by 10:30 it was around 82. It finally topped out at 94.5 around 1:30 – 2 and then gradually started to drop and the sun changed position. By 4:00 I still had 65 degree air coming out of the vent. By 4:00 the sun had little effect on the box anymore.
If I decide to build another one, I would make a couple of modifications. 1. Baffle the heat tubes more to slow the air down through the tubes. This will allow more heat build up. 2. Add a connection piece on the top and bottom near the glass (acrylic) where the heat tube panels are located towards the outside. More experimenting to follow.