Is there any "safe" method to do this? I did a google search and came back with industrial products, but no residential prosucts.

I have a System 2000 boiler and hot water tank. When the furnace is firing, the temp of the exhaust through the flue is around 400 degrees.

That seems like a horrible waste of heat.

Same thing with the dryer. It throws heat right outdoors, which also seems like a waste. (not really concerned with humid air, as it is winter and I have to run a humidifier anyway).

Any tips, products, or other recommendations would be appreciated.

thanks!