Add-On Vent Dampers - Oil or Gas

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Old 11-07-11, 05:31 PM
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Add-On Vent Dampers - Oil or Gas

The following is an off-shoot of another thread, copied here:

Install an 'Oil Vent Damper' ( OVD ) on your system. These dampers will close the damper on the flue pipe after the burner shuts down (and of course open it before the burner fires up!). This prevents heat loss up the chimney during off periods.


image courtesy Patriot Supply - Industrial, Commercial & Residential HVAC Parts & Equipment

This would keep the heat in the boiler for much longer! I bet the savings on this device would equal or surpass the 'so-called' savings that is claimed for the HW.

I just installed one on my own system... data collection commences soon!
 

Last edited by NJT; 11-08-11 at 04:50 PM.
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Old 11-08-11, 04:40 PM
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Regarding the automatic vent shut-off damper: I've been thinking about adding one to my gas boiler flue. It would be mounted downstream of my conventional barometric damper. Do they have to be mounted in a vertical orientation or can they be in a section of flue that is, say, 30 deg from horizontal, sloping upward? I assume the damper drive motor is 24V?
 
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Old 11-08-11, 04:48 PM
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We're kinda gettin' off justymis' original topic... but since I brought it up... I'll move this to new topic and continue:

With gas, you would of course use the "GVD", I haven't installed one so don't know if it's 24VAC or 120VAC... I suspect the former. Field Controls has the I&O available on their website. [I just checked, the GVD is 24VAC] The GVD does NOT come with the wiring harness... ordered separately ... and presumably to match the boiler you have, there are several adapters.

Gil, your boiler has no 'atmospheric hood' and uses a standard baro damper? (I think that's what yer saying...)

On the OVD, the damper itself is mounted not less than 2" downstream of the baro damper. It can be mounted vertically or horizontally, or anything in between. There are limitations in the radial position of the motor when mounting horizontally. ( heat, condensate drips, etc ) I suspect that the gas damper is the same in that regard.

The OVD comes with a 'blocked vent switch' and wiring harness. The blocked vent switch mounts as close to the boiler as possible, in a 3/4" hole in the pipe, and not more than 24" from the damper itself. So basically, it's ' boiler / BVS / Baro Damper / Damper / to chimney'

The OVD requires 120VAC H&N (with ground) and two wires that go in series with the oil burner motor control from the primary. The wiring 'whip' that comes with the OVD goes into one of the knock-outs on the j-box under the primary control on the burner.

I'm hoping it saves me a few percent... might pay for itself in 3 years or so if it does...
 

Last edited by NJT; 11-08-11 at 05:07 PM.
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Old 11-08-11, 05:26 PM
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How are you planning to measure the efficiency improvement with the damper? Here's an idea:

With steady outdoor weather conditions (wind and temperature), and starting with the same boiler temp after burner shutdown, measure the time required for the boiler temp to drop X degrees - first with the damper shut and then with it jacked open. Knowing the boiler water volume, the different Btu/hr heat losses should be able to be computed?

I'm holding off installing one because of the geometry involved with my flue - an 8" elbow partially extends into where the flue damper would need to go. So, I'm anxious to hear any results of your installation.
 
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Old 11-08-11, 05:54 PM
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I've got a few years worth of data collected on oil consumption versus degree days. I have an elapsed time meter (actually a 24 hour wall clock) wired such that it runs whenever the oil valve is open. Knowing the firing rate of the burner and the time it burns allows me to have a fairly accurate fuel usage data stream.

Download weather data (degree days) from local weather stations...

Calculate the 'K factor' ( degree days per gallon ) and chart on Excel spreadsheet.

I won't have any data that's 'out of the noise' until spring time probably, but I might be able to see a 'trend' before that. I haven't started collecting any data yet... probably won't for at least a few more weeks. Using an entire heating season tends to average out the sunny/cloudy windy/calm rainy-snowy/dry daily differences.

I don't expect to save as much with the OVD AND the post-purge circulator as I would with the OVD alone. Since the boiler will be cooled to about 95F by the circ running on after, there won't be as much heat to lose up the chimney. In other words, the OVD by itself would probably save more than it's going to save when in conjunction with the post purge.

I can tell you that the circulator idea appears to have saved about 2-3% in fuel use... relative to degree days. That's about $50-$60 a year at today's oil prices. Best is that the payback was instantaneous... the install was FREE, even the strap-on aquastat I had in my 'junk box'.
 
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Old 11-08-11, 06:08 PM
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I use Heating & Cooling Degree Days - Free Worldwide Data Calculation for easy degree day downloads.
 
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Old 11-08-11, 06:13 PM
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YES! I think you turned me on to that site last year or the year before... They get their data from wunderground.com I believe... as I had done previously... but that little app is great!

The only thing better would be your own "Johnson Degree Day Meter" in the backyard streaming live data to a computer and automatically updating the charts.
 
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Old 11-08-11, 06:27 PM
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I like this type of discussion on how to save on fuel as this is my nitch in the heating market and as we all know the era of cheap fossial fuel is over .The U.S. and Canada wasted the last 38 years developing solar.
 
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Old 11-08-11, 07:09 PM
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I think the days of cheap ANYTHING are over.
 
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Old 11-08-11, 07:12 PM
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Originally Posted by NJ Trooper View Post
YES! I think you turned me on to that site last year or the year before... They get their data from wunderground.com I believe... as I had done previously... but that little app is great!

The only thing better would be your own "Johnson Degree Day Meter" in the backyard streaming live data to a computer and automatically updating the charts.
Hah. I have a weather station in my backyard that uploads to wunderground.com. So I could almost do that. I stick with getting my degree days from Newark Airport though for accuracy and fair comparison to past usage.
 
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Old 11-08-11, 07:46 PM
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I've found quite a disparity in the data further nawt in Joisey... even the airport nearest to me has quite different data than that which I've recorded on my own. But, when tracking how various improvements are saving or not, it's most important to use consistent data... at least you will be comparing apples to apples... sorta.

I mean, even if the station you choose is consistently cooler or warmer, and the actual accuracy is off, your RELATIVE measurements will be close enough.
 
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Old 11-09-11, 04:56 PM
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That's what I figured. Newark is definitely not the exact temp that I am. Especially during the summer. I find a noticeable difference between my station and others very close by.
 
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Old 11-09-11, 06:41 PM
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Troop,
My dad had an oil vent damper installed on his boiler during the "oil crisis" of the '70's & it paid for itself (material & labor) in less than one heating season.
In all fairness, it is 43', as I recall from when I installed a stainless liner about 10 yrs. ago, from the breech to the top of the chimney. He also had a 1954 National Radiator boiler firing 1.35 gph with a domestic coil.
On a cold & windy day you wanted to keep pets & small children away from the barometric less they disappear up the chimney.
 
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Old 11-09-11, 07:15 PM
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I bet it's running an 8" flue pipe! 43 feet! I bet that chimney sucks!

I've only got about 18' or so up there.

That's good to know that it might save that much, I certainly HOPE so anyway!

One thing I'm wondering about though... if it might be a good idea to increase the 'pre-purge' (valve on) delay to compensate for the 5 seconds it takes for the damper to open?

wait... hang on... I don't think the pre-purge time is selectable... fixed at 15 secs... oh well.

I was thinking when wiring this thing that it seemed strange that they would install into the motor wire, rather than the 'limit' wire.

Why NOT the limit wire? It would achieve the same purpose, and not 'eat up' 5 seconds of the pre-purge cycle.

Can anyone think of a reason that Field recommends wiring to the orange motor wire rather than the red limit wire?
 
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Old 11-09-11, 07:27 PM
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I think I just answered my own question...

If wired to the LIMIT wire, when the heat call ended, the damper would close 30 seconds later. That's the fixed timing built into the OVD.

If the POST-PURGE (motor off) delay is LONGER than 30 seconds, then the blower would be blowing against the closed damper and dumping combustion stank into the building due to the positive pressure in the boiler...

Yeah, the 30 second 'countdown to close' has to begin when the motor stops... wire like the manufacturer says! Don't try to second guess them!
 
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Old 11-09-11, 07:27 PM
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I think it was a 9" flue pipe, but coulda been 8" or even 10". The memory hain't that good these days.

All depends upon how it's wired. If you power the damper off of "B1", then upon closure of the end switch it sends power to the primary, you shouldn't need to increase the pre-purge. If on the other hand, you are powering the damper & burner motor at the same time (not a good idea), YES, you need to increase the valve on delay.
 
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Old 11-09-11, 08:46 PM
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No, I would never power the burner and damper same time! dat's crazy!

The OVD gets power from constant 120VAC, and the output wires in series with the motor wire...
 
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Old 11-10-11, 05:40 PM
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I know you knew better but wise folk have been known to do some not real schmart tings.
 
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Old 11-13-11, 02:09 AM
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LOL!! That's why I love this site...You guys are real "How To" geeks!
I have 3 brand new "BURNHAM" gas steam boilers for a radiator system. They all have the gas vent damper (GVD), but it's connected directly on top of the exhaust hood/duct of the boiler.
The automatic damper has it's own power conduit connection coming from the main electrical box.
On mine, the damper always opens automatically before the boiler can fire!

That's all I got........PEACE......
 
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Old 11-13-11, 09:17 AM
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And we love all our 'listeners' too!

One other thing I'd like to note... if anyone is installing one of these...

On GAS SYSTEMS, with a STANDING PILOT, do NOT install the 'plug' into the hole in the damper plate. You need a minimum draft through that hole to vent the combustion products of the pilot.

On GAS systems WITHOUT a standing pilot (i.e. HSI, or SPARK ignitor) and OIL systems, the 'plug' should be installed.
 
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Old 12-13-11, 11:30 AM
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NJ Trooper

Need help. Pls call ................
 

Last edited by NJT; 12-13-11 at 03:18 PM.
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Old 12-13-11, 03:18 PM
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Sorry Tom... not the way it works.

You have a question or a problem, post it here and someone will help you.
 

Last edited by NJT; 12-13-11 at 09:24 PM.
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