Power Venter post purge

Reply

  #1  
Old 12-15-08, 07:15 AM
Member
Thread Starter
Join Date: Aug 2008
Location: Boston
Posts: 60
Received 0 Votes on 0 Posts
Power Venter post purge

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?
 
Sponsored Links
  #2  
Old 12-15-08, 07:41 AM
Join Date: Aug 2006
Location: usa
Posts: 902
Received 0 Votes on 0 Posts
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...
 
  #3  
Old 12-15-08, 02:29 PM
Member
Join Date: Dec 2008
Location: United States
Posts: 158
Received 0 Votes on 0 Posts
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.
 
  #4  
Old 12-15-08, 05:19 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 13,943
Received 5 Votes on 5 Posts
Unhappy Oil fired & power vented

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.
 
  #5  
Old 12-15-08, 06:53 PM
Member
Thread Starter
Join Date: Aug 2008
Location: Boston
Posts: 60
Received 0 Votes on 0 Posts
Originally Posted by Grady View Post
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?
 
  #6  
Old 12-15-08, 07:37 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 13,943
Received 5 Votes on 5 Posts
Bad Combo

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.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: