Fireplace Heat Exchanger

For a while I have been thinking about how to make our fireplace more efficient. Modern fireplaces are not efficient and are known to suck air from inside the house and send out of the chimney. That lost air is replaced by much cooler outside air, resulting in a net heat loss (less the heat radiated by the fire).

Calculating the exact heat loss is difficult, but the way I look at it is: most of the heat from the fire is going up the chimney and while the fire may be heating the room, it's actually cooling the rest of the house.

So I decided to make a heat-exchanger grate to use in the fire place to see if we could "reclaim" some of the lost heat. The concept of a heat exchanger is for the fire to heat metal tubes which circulate and heat air that can be directed back into the room.

The first step was to acquire the tubes. I considered bending my own, but it was much easier to purchase some already bent to shape. I used some wood supports to keep the tubes in position prior to welding:

Heat-exchanger tubes aligned with wood guides.

I needed to bend some metal rod for the leg supports. This required some ingenuity as using a propane torch did not get the metal hot enough to easily bend. With the help of a jig and hammer I was able to bend (or break) the metal for the legs:

Metal bending jig for the legs.

With all the metal pieces all setup, I was able to weld everything into position. This was a bit harder than is sounds and even with the wood in place, it was hard to get everything lined up:

Ready for welding.

After a few welding, grinding, adjusting, and more welding cycles, things were looking good.

After welding, almost ready for paint.

I added a coat of high-heat paint and the heat-exchanger was ready for testing. Would it really make our fires more efficient?

After paint, ready to test.