Anyway to make oversized boiler more efficient ?

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Old 12-12-07, 11:52 AM
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Anyway to make oversized boiler more efficient ?

After doing some extensive reading I see my boiler is oversized for my application. Here are the specifics :

Slant Fin Intrepeid hot water boiler with tankless coil(coil not in use)
Boiler has 1.10 nozzle rated for 154K BTUH
L8124c aquastat, R7184b primary control
The 8124 is set at 180H 140L with 20 differential
5 zones with zone valves one of wich is an indirect water tank
Slant Fin HE2 calcs say heat loss is 67,200 BTUH, house is a 1964 split level.

Can I use a smaller nozzle to improve efficiency ? The Beckett AFG burner says nozzle size of .85 to 1.35. What are the consequences of underfiring this boiler ? Any other suggestions or advice ?

Edit: There is a Beckett Heat manager installed on this system.
 
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Old 12-12-07, 12:20 PM
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According to the I&O manual with a beckett you can go down as low as 1.00 gph. I would not go below that. If you have a heat manager on the boiler you have about the best you can do short of replacing the boiler with the proper size boiler. There is an outdoor reset control available but I am afraid the boiler would short cycle and reduce the AFUE efficiency.
 
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Old 12-12-07, 03:49 PM
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I worked for Slant Fin about 15 years ago when state of the art was the Liberty 30 (L-30PT). At that time you could order it H (high performance) and you could do a little playing around with different nozzles and burners. Today, as like the car manufacturers do also, what the specs say is what you should use. You can no longer (for most cars) order the engine you want, the tranny you prefer, the rear axle ratio you want, (not to mention almost everything today is FWD). Same holds for boilers. About 10% is all you can safely play with before you start affecting other factors such as recovery time, to name one.

The Intrepid you have should not be fired with a smaller nozzle than a 1.00 UNLESS you have access to instruments to make the necessary corrections in combustion, or have a qualified technician do it. Also, the BURNER says 0.85 to 1.35-----correct? That burner is used on hundreds of different boilers and furnaces. That is the burner specs., not necessarily the boiler specs. Are we on the same page?

Keep in mind If you decide to go lower than 1.00 you may affect the rate at which the system recovers, which may be ok in your case since you are not worried about domestic HW directly, and I'm assuming you do not have 8 people in the house all taking showers within three hours of each other. It may take a while to heat up the house if the doors are left open for a while in middle of winter while bringing in all those gifts, or may take a longer time heating up once you get home and kick on the thermostat, etc. but you should be able to get it down to even a 0.90 (a little harder to find though) but you MUST have it re-calibrated for proper combustion. This is a MUST!


In my judgement, speaking from experience, a house built in 1964, unless you have completely re-insulated the entire house, and an indirect water heater say 50 gals., with 4 separate heating zones, even assuming not all 4 heating zones are going to demand at the same time, is just about going to make it on 0.90. Try it, but my guess is you will go with the 1.00.

I hardly ever find a satisfied customer when a 0.90 or 0.85 nozzle is used in a split level house with an indirect WH who has 4 heating zones, and has an Intreped boiler. Oh I've done hundreds of houses with the same exact configuration! JUST KIDDING!!!!! Never had the same EXACT SCENERIO as yours.

By the way, if I were you, I would stick to either a 1.00 or 1.10. It's what makes sense.

Good Luck, Charlie
 
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Old 12-12-07, 04:10 PM
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Thanks for the responses rbeck and boilersrus. I have the boiler cleaned and serviced every year (in February) so maybe I'll have a 1.00gph 80degree nozzle waiting for the tech to install since I don't have the calibration equipment or the skills to use it. Do you guys think a tenth of a gallon reduction in nozzle capacity will make a noticible difference in my oil consumption ?
 
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Old 12-12-07, 05:55 PM
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If it really is .1 gph less oil, then how about:

every 10 hours of firing time, you save a gallon. Say you fire 10 hours a day, for a hundred days. That's a hundred gallons. At $3/gallon, that's $300. I'd notice that....
 
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Old 12-12-07, 06:19 PM
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I imagine that be pretty much absolute worst case though... 10 hours a day is a lot of firing ... works out to about 58K BTUH ... which might only be needed for a few percent of the total heating season, certainly not for 100 days!

I wouldn't be surprised if you saved $100 though! That $4 nozzle would sure pay for itself in pretty much no time ...
 
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Old 12-12-07, 07:55 PM
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Originally Posted by xiphias View Post
If it really is .1 gph less oil, then how about:

every 10 hours of firing time, you save a gallon. Say you fire 10 hours a day, for a hundred days. That's a hundred gallons. At $3/gallon, that's $300. I'd notice that....
Does it work that way??? I'd think the BTUs are still being used for heating the room. Smaller nozzle means longer firing times, so that $300 dollars isn't "real" in that sense.

My opinion is that downfiring the boiler would do two things that would provide savings:

1: Increase the boiler efficiency as the stack temperature would be lower.

2: Increase the overall efficiency based on the increased run times--that reduces the amount of heat lost up the stack when the boiler is idle and cooling.

Possible third benefit is lowered short cycling during the shoulder seasons, less wear and tear on the equipment.

Pete
 
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Old 12-12-07, 08:11 PM
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You guys sure know how to re-inject reality into a bit of idealism.

Joe C, pay no attention to me on this one. They are being serious, and make good points.
 
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Old 12-13-07, 07:22 AM
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Thanks guys for all the responses, I love the debate . Lots of good info for me and others looking to save a buck.

Lets see if I understand this statement, a lower stack temp means more BTUs' are going into the house vs the stack ?

Originally Posted by radioconnection View Post
1: Increase the boiler efficiency as the stack temperature would be lower.

2: Increase the overall efficiency based on the increased run times--that reduces the amount of heat lost up the stack when the boiler is idle and cooling.

Possible third benefit is lowered short cycling during the shoulder seasons, less wear and tear on the equipment.

Pete
The boiler does short cycle at times even during sub freezing temps depending on the house conditions. In my situation(split level house) a call for heat on the top level can trigger a call for heat on a lower level just after the boiler has shut off, then it turns on again for maybe 2 minutes once the hot water in the boiler was used up to satisfy the tsat on the lower level. Hope that makes sense.
 
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Old 12-13-07, 11:01 AM
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Getting back to reality, also remember when you reduce the firing rate your thermal efficiency goes down. The best transfer of heat is at the proper firing rate. Fill the flue passages and it will slow down the flue gas travel thus more thermal transfer.

This applies to chimney vented, power vented and direct vent products but not mod/cons as they vary the fan speed. Being able to change the fan speed makes a difference.
 

Last edited by rbeck; 12-13-07 at 11:04 AM. Reason: Added last paragraph to avoid confusion.
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