me again v/c question temp b-vent

coaly said:

It should not be that hot.
How do you know how hot the flue gasses are entering the exhaust pipe?
Are you sure you're not missing a divertor hood?

That is an INTAKE on the exhaust allowing indoor air to mix with the hot exhaust gasses rising up the pipe.

Notice on the water heater you mentioned, there should be a large air intake around the exiting pipe. This is found on all vented gas appliances. This keeps the inner pipe cool which could be aluminum that melts easily.

As hot exhaust gasses rise up the pipe, it creates a low pressure area in pipe and appliance connector. This is called and measured as draft.

Atmospheric air pressure is greater outside of the flue pipe, so air rushes in mixing with flue gasses. This cools the gasses as they rise, slowing them down, reducing draft. Too much draft causes too much heat loss up the flue pipe, lowering efficiency of appliance.
Exhaust gas temperature from the stove should be much lower. That efficiency rating is when connected properly. You are probably much lower.

Excessive draft also affects air flow over burner and can affect the correct air pressure needed (atmospheric pressure) to push into air intake of burner.

The connector parts for natural venting in the manuals you've read are for admitting this indoor air up the stack to cool it. Called a "divertor hood".
There may be a built in divertor (intake) in your appliance. This is only used with natural vented appliance. The test to see if the flue pipe is drafting properly on a gas appliance is to light appliance and shake out a match to watch the smoke rush into divertor and up the stack. This shows air flow moving into exhaust. Without proper draft, CO from combustion can leak back into home. It should have a spillage switch. (a high temperature switch that senses high temp exhaust gasses in divertor hood which should be cool incoming air from room) This switch is connected through thermocouple circuit to shut down appliance when the correct draft is not sensed. Since you changed the gas valve, are you sure all safety switches are connected in the circuit properly?

I'm not sure what you mean by "test mode", but the appliance shouldn't work properly connected to a short test exhaust pipe. With proper venting and divertor, it requires enough vertical pipe above roof to cause enough draft to exhaust products of combustion. This height will be specified in manual. The appliance won't work properly without it. The exhaust isn't just a pipe to let the exhaust fumes and CO out. It serves other purposes to make the appliance work.

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