Improving the cabin heat on a stock 170

[Bruce Fenstermacher]

Buck

I have several hours flying in both a stock 170A with the normal "2 scat and center heat option, my 170A with the one 2" heat valve which is the same up to including '52 B models and a '53 with the improved heater and AVCON 180 conversion.

The AVCON conversion witth the different muffler system puts out more heat for some reason than the Continental/Hanlon Wilson setup. You didn't what year you have but the fact that you are connecting to the heat valve with 3" scat indicates that you have the later inproved heater setup. As-is with no modifications your setup will perform the best of all the 170 heaters and as well as most GA airplanes I've flown. I'm in PA north of Philadelphia. Certainly not as cold as MT but still pretty cold.

As I understand your mod you have essentially a 3" scat we'll call the heater side and a 2" scat we'll call the carb heat side going to a y with a 3' inch exit.

I doubt if this will work any better than just the 3" scat going directly to the heater. You are trying to jam 3" of volume from the heater side and 2" of volume from the carb heat side through the one 3" hole at the heat valve. In fact you may even lose heat if the pressure of the 2" carb heat side is lower than the 3" heater side.

I could be wrong. Just my thoughts.

As for a scoop at the intake. I have seen several setups here when 2" scat is used from no scoops at all to one scoop on either side and scoops on both sides like mine. This of course would be on early 170s without the preassure cowl but with the preassure box inside and the different grill front.

I can't recall ever seeing any scoops when 3" scat is used on later models with the pressure cowl and different grill.

[GAHorn]

I have a concern with "stealing" air directly from the carb heat box. That 2" opening is below the carb where fuel can enter the cabin air supply. During shutdown especially, fuel can pool and noxious/explosive fumes can enter the cabin ventilation system. Inflight application of carb heat will introduce unheated, cold ambient air to the cabin heat system and/or will allow a loss of cabin heat system pressure, and will reduce the effectiveness of the cabin heat.
Also, that modification is an unapproved one and would require a basis of approval. Fuel systems and ventilation systems require safety protections against mixing the air. (The earlier, approved, "Y" set up is not below the carb bowl and is located farther upstream in the high pressure area.)