Hi Bob;
Your cabin heat system in your airplane carries heated air from a plenum on the firewall outward to two aluminum boxes that carry the heat along the left and right sidewalls to the aft cabin. From there the heated air exits through little vents into the back seat area. The heat to the rear seat is controlled by levers on top of the center console. Make sure those levers and the doors they control are working properly.
Obviously when the heat in the boxes gets to the back seats it is cooler and since the box get smaller in cross section at the aft end, there won’t be as much heat in the back as in the front.
One thing that can be done is to plug holes and spaces where air can get into the cabin. I’ve seen where the fresh air vents in the leading edge of each wing are blocked off during cold weather months. Check to see that the fresh air vents are closing tightly. There are holes in the fuselage walls where the wing center section, control cable and wiring pass through. A small hole can let in a lot of cold air. Covering those gaps with tape will help.
I suggest that you get a carbon monoxide detector for the cabin of your airplane. The heating system of almost all small airplanes ducts ram (fresh cold) air around the engine exhaust collector, where it’s heated then ducted into the cabin. Any leak in the engine exhaust collector will allow exhaust gasses into the cabin. These gasses are very toxic since they contain carbon monoxide. In my opinion, working carbon monoxide detector must be installed in the aircraft cabin when cabin heat is used.
Personally, I fly in temperate regions and due to a very thin firewall, there’s always enough heat at the front seats in my airplane and because I know how insidious carbon monoxide poisoning is, I never turn on the cabin heat in my airplane. I do carry a light fleece blanket in the back seat for cold days.
In my opinion, the small stick on CO detectors that change color in the presence of CO are close to worthless. Others may have their opinions such as they are better than nothing but in order to be effective they have to be in a pilot’s immediate field of vision. If you go for one of these, the Quantum Eye ones are a little more expensive but are worth the cost.
Let me know what you find, or just to buy a small fleece blanket for your rear seat passengers.
Steve
