Hello Larry, I remember your thread...larryfoster wrote:Last year I had a 40+ page thread.
In it, I was told that I would have to block off the return to my propane furnace if I wanted to use it for my coal furnace.
In other words, it sounded like I could use it for one or the other but not both if I wanted my propane for back up.
Did you do that so you use only coal or can use either/both furnaces at any time with "switching between?
Yes I did make an directional air flow control for my oil furnace. It actually allows me to run both if I need to at the same time. I did that so I could use the blower recirculate feature on my furnace. I'll post a picture of it later.
But, with that said, all you need is something solid cut the exact same size as your air filter. Like a piece of plywood or even a political yard sign. When you want to run your Hotblast furnace, you pull your air filter out and put this piece in. This will separate the cold air return from the supply in your propane furnace so it doesn't just recirculate a large percentage of the air. When you want to run your propane furnace, pull that piece out and put your air filter back in.