Heat valve

[Craig]

I was thinking about the cabin heat valve, and it's operation. I'm getting the stainless steel cabin side unit that is like the one from Van's, but this question applies to the firewall side unit as well.

If the valve is open to the full hot position, all the heat from the heat muff goes into the cabin. No problem.

If the valve is closed to the full cold position, all the heat from the heat muff goes overboard. Again, no problem.

If the valve is in an intermediate position, some of the heat from the heat muff goes into the cabin, but the potential problem that I see is that the valve is now halfway open to any gases, fumes, or fluids in the engine compartment. Is this a problem?

[Kahuna]

Pressures on the top of your plenum are higher than under. Regardless of the volume, you should continue the higher pressure air source from the plenum area and not have any possibly contaminated air backflow on you.

[Craig]

I think you misunderstood my question.

I'm not worried about plenum air.

The valve on the firewall, when it is partially open, is a direct opening to the forward side of the firewall.

[Kahuna]

So what are your concerns?
Fire?
CO?

[hydroguy2]

Originally Posted by Craig

I think you misunderstood my question.

I'm not worried about plenum air.

The valve on the firewall, when it is partially open, is a direct opening to the forward side of the firewall.

I think he understand your question, I think you didn't understand his answer.

The high pressure source to the heat valve is always from the plenum via the heat muff scat hose. During an intermediate opening of the heat valve, flow would be from the scat connection with partial flow to the cabin and partial flow into the engine compartment.