4 ms·

That's a great idea. Modern gas boilers and tankless water heaters often run their exhaust and intake in concentric pipes, so that the outgoing hot air warms th

That's a great idea. Modern gas boilers and tankless water heaters often run their exhaust and intake in concentric pipes, so that the outgoing hot air warms the incoming cold air.

abthomson 18y ago
Furthermore, the flow in the two pipes is usually in opposite directions because it's more efficient that way.
- pingswept 18y ago
  I think that the intake and exhaust are always in opposite directions, regardless of whether it's efficient.