The all stainless steel heater bypass box was conceived while looking at aluminum hardware used for sealing the firewall on experimental aircraft. It didn't make much sense to try to seal a stainless steel firewall with aluminum hardware. It is well known in the metal working world that stainless steel melts at 2600 degrees and aluminum melts at 1200 degrees. What most pilots don't know is that windblown avgas burns about 1875 degrees. And so, work on the all stainless steel heater bypass box began.

The all stainless box withstood the torturous flames for 10 minutes without failure. A good first test. Then the aluminum box was tested. In only 16 seconds the aluminum was a liquid puddle at the bottom of the simulated firewall. Only 16 seconds, you might not even know you have an engine fire in that time. This was an eye opener.

Once the all stainless steel heater bypass box was in production, the fun part began. Testing initially was a challenge because a simulated engine fire was required. But how hot does windblown avgas really burn? Our tests showed that windblown avgas burns at 1875 degrees. Now the test bed was in place.

Three models of the all stainless steel heater bypass boxes are offered. The engine side control lever comes with a backing plate that attaches to the cabin side of the firewall and has a 2 inch scat tube outlet so a tube can be attached in the cabin that directs air where wanted.

All stainless steel construction offers a fireproof closure in case of an engine fire.

New flapper design offers better seal to keep out hot air when closed.