I have an oil fired Superior boiler and a Carlin EZ1 burner. My power venter has an adjustment for the length of time it runs after the burner shuts off (post purge?). What determines the length that this cycle should be? Years ago the service company turned it to the longest cycle and during heating season it seems like it never stops. During this years tune-up when I asked about this the tech told me we can just shorten the delay. It is nice having the power venter turning off quicker. My concern is that after 10 years someone just happens to turn the delay down without any testing or timing. Is there a rule of thumb for this delay? Is it better to cool the boiler down as much as possible after the cycle or is it better to leave as much heat as possible in the boiler to allow a slower cool down?

 

I'm not a pro, but too long a post purge is just sucking cold air through the boiler, cooling it down, and doing the exact opposite of what you'd want! Back in the days of the first oil shortage
they were selling electric dampers that closed and stopped thermal air flow through the stack pipe when the burner was off, to stop heat loss.

I'd think the post purge should be long enough to remove combustion gases from the system. But again, check with a pro...

 

Rule of thumb is to calculate how long it takes to evacuate the chamber, vent pipe and ventor of combustion gases and running any longer is stealing conditioned ambient air and cooling block. This with dilution air from barametric mixing must be calculated. Not and easy task, some use math, some fast acting temp measuring and others sense of smell (if you smell combustion products at the barametric after fan shuts off, make it longer.

 

Oil fired & power vented is just plain a bad combination. The most common reason for an extended post purge time is reflected heat causing after drip from the nozzle & causing fumes. Often setting the post purge time is a matter of trial & error in a particular application.

 

Unfortunately that's how the house was built 10 yrs ago. While I would love a chimney, it isn't happening in this economy. What makes this a bad combination?

 

They are just notoriously troublesome with fumes, stains on the side of the house, lockouts, etc. In my area we often, not always but often, encounter them on a horizontal furnace in a crawl space. In these conditons, rust is a big problem as well.