I have a Tappan forced hot air system model # GUF 105 D E5
It's a 105,000 BTU size. A repair man said the exhaust output was 4000 units and it should be around 100 units. He replaced the gas valve with one he had in his truck and I think it's the wrong size. He adjusted the valve somehow and got the exhaust reading to 200 units. Is it the wrong valve? It's a Honeywell #VR8300A4508. It looks like most valve sizes are for 150,000 BTU units. Is this right?

Thanks,
Don
(I hate to get ripped off)