De Rating a gas burner (residential steam boiler)

John Lasky

good after noon.

many thanks for all the help, my noisy steam baseboard is all set, and most problems are solved.

I need to de rate my boiler

I called 2 different manufacturers,and got 2 different answers.

My boiler has a rated max input of 165,000 BTU ,net 130,000 BTU

I did a calc and I only need an input of around 100,000 (im running at 104,000 at the moment) input net at arond 80,000+- my load is 331 cu ft Including piping.

right now I have the pressure lowered (alot) No CO in basement (lots of detection even near floor) but I know I am producing CO in chamber as the flame has a blue base but plenty of yellow tipping.



Boiler company # 1 (MY BRAND) got real nervous when I asked about de rating (even though I build their draft control panels for them and bought my boiler factory direct) they would not give me any info other than I can turn the gas pressure down and said that was the end of the conversation and it was.

they would not even tell me the thread diameter of the orifices.

Boiler company # 2 (very very helpful) advised Not to turn ever down the preasure unless its to high but to change the orifices to a smaller size, This tech support advisor gave me a ton of info without any hairy eyeball.

Now I just saw a post on this board that mentioned removing burner racks and plugging off. That might work as that would be very close to what I need!!!

my boiler has 5 burners if I turn my preasure back up to where it should be and remove the 2 outside cans Ill be at 99,000 +- input which is very close to where it should be.

again Im at 104,000 input right now but need to get the flame right. I know its the FLOW not pressure that needs to be reduced.(I just needed to see if I would heat ok at around 100,000 btu, the system never worked better than when I lowered the firing rate!!!)

so .

1) Should I order a set of 5 orifices and have them plugged/re -drilled for the 35% or so de rate

(its an atmospheric burner)

2) remove the 2 outside burners and plug the maifold as the input with 3 burners will just about right. (if yes what do I use for plugs, or where can I get blanks, bolts ???)

I do a fair amount of business with an industrial burner company, they can get me the orifices but I cant take one out of my boiler to bring to them to match up at this time (ill have no heat for 4-5 hours)


Any suggestions will be welcome

many thanks "John"

Steamhead

Paging Tim McElwain!

If it were up to me I'd go with the manufacturer's recommendation- but only after talking to Tim. He's the best IMHO.

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JohnNY8

I've been told by many that plugging an orifice to a burner tube is a bad thing to do but I've never gotten a satisfactory answer why.
Buderus makes a boiler with two independent burner setups under one heat exchanger. When you need one, it fires one, if you need two, the second one fires.
It's exactly the same thing, most of the time, and it's lauded as a technological breakthrough.

I'll follow this post closely as I'm curious as well.


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John Lasky

Im baffled too.

Hi john in NY. Im a John IN NY TOO.

the gent that owns the burner control supply company I do business with (I do industrial controls)he said lowering the gas rate by shutting down a section/s or using smaller orifices is no big deal!!

hes done it a bunch of times and sees it done a bunch as well. if it doesnt work to your liking change it a bit but no real harm done unless the stack temp is way out of norm. but my unit is an atmospheric gas unit and stack temp (according to him) is not that critical .

Im curious myself for a decent answer.

I cant see that the technology is SO different between manufacturers that one says turn the gas pressure down and the other says derate mechanicaly by using smaller orifices and that gas pressure should never be adjusted!!??. I tend to agree with #2


they both have the same gas burner and plain jane valves for the most part.



?????


Lets see what we can learn.

"John"

Wild Bill

Gas boiler downfire

Hi,
The first two suggestions are the best, check with Tim M. and the manufacturer.

However, as a former employee for a boiler manufacturer, please allow me to throw in my two cents. In an atmospheric boiler, the base area (where the burner tubes are) is the most highly concenrtated heat area, and should be kept somewhat "consistent". We would suggest that someone doing a downfire get new orifices drilled for the proper size, install them in ALL the burner tube area on the manifold. This would eliminate any potential hot and cool spots in the base area. I hope this helps.

Wild Bill

EBEBRATT-Ed

Hopefully TIM McELWAIN will see this

he is the expert. As far as removing burners I think you have a lot of secondary air going along for a free ride and cooling the boiler lowering stack temp.

I would think plug and redrill would be better if you can make the primary air adjustment match the new input. BUT Tim's the expert on this.

John Lasky

thanks wild bill

This makes the most sence! actually thats what Boiler manufacturer # 2 advised.

I can see where removing a rack from underneath a section could cause a cold spot.

I attemted to order blanks from my boiler mfg but to no avail (I tried to directly as I do business with them now)

looks like ill have to order a set from a distributor and have them plugged/drilled.

Again the burner supply Company I go to probably has the orifice blanks on the shelf but I cant take one out of my system long enough to try and match it up. and the Manufacturer will not give me any info on them at all (and I build their commercial draft control panels)

many thanks Good info "John"

Jim Davis_3

Derating

The least of two evils is blocking off orifices never lower gas pressure or put in smaller orifices.. Much of the heat transfer from a burner is radiant(60%)and is the greatest area of transfer. Making the flame smaller in any manner greatly reduces radiant transfer. Second the gases from the burner must scrub the balance of the sections but with reduced input laminar flow will develop which means the sections will see the coolest part of the gases instead of the hottest. The next problem with either is the flue temperature above the drafthood. The amount of dilution air brought in from the room will remain fairly constant but now the percentages of hot gases is reduced. If the temperature above the drafthood falls much below 230 degrees the gases will most likely condense before they reach the top of the chimney. What pressure are you operating the boiler. Using a vaporstat and operating at 8oz instead of 2# or 3# would be a better direction initially. This will actually save you fuel. Blocking orifices may not really save any fuel cost, just create longer cylce rates. Cutting back gas pressure or putting in smaller orifices is guaranteed to increase fuel costs if it is more than 15% of the rating.

EBEBRATT-Ed

I beleive that most orfices are 1/8" pipe thread-take one out and try it in a 1/8" fitting. You could plug it temporally to take to the supply house.

John Lasky

boiler presurre

Hello .

I have cut out set for 1.5 lb cut in set for .5 lb.

I originally started adjusting things as my presure was too high and my cycle time at 165,000 input was only 2 mins on when the system is hot.

I have all 2 pipe baseboard on the first floor and one pipe rads on the second.

total square footage including pipe is 331 now my boiler according to the manufacturer capacity at 165,000 is 421'

that only 22% difference so where should I be on gas input??



also how does the vaporstat work at such low (oz) preasure??

how does it prevent the dreaded short cycle or is the short cycle thing way over rated.

many thanks "John"

Jim Davis_3

When all things are mechanically sound short cycling can be over stated. Operating at 8oz the pressure should drop to as close to zero as possible. Condensation has been one of the issues of short cycling but that is caused by low inputs, low flue temperatures and too much dilution air in the drafthood.

Unknown

John Lasky, I need a little bit of

information and I think we can help you out.

1. What make and model boiler is this?

2. Is the bottom of the boiler open or closed?

3. What does the rating plate call for on gas pressure?

4. Is this Natural gas or LP?

5. You state that you bought the boiler direct, why was it oversized to begin with?

6. If it is natural gas have you clocked the burner to determine what the actual amount of gas being used is?

7. What is the Make and number on the gas valve?

Now some information that will help you. First of all I am not a big fan of derating boilers. I realize that manufacturers typically allow up to 20% reduction but my experience with derating over the years has not been good. It can be done but you have to really get a lot of things correct when doing it.

Your boiler at 165,000 input with a net rating of 130,000 cannot be fired at less than 130,000 (the math on that is close to 20% by the way). So fire it at 130,000 minimum no less and depending on what boiler it is I may recommend 140,000 as a minimum.

So if we go with 130,000 at 3.5" W.C. that is 26,000 BTU's per burner that would require a 41 drill size orifice. At 4" W.C. pressure a 42 drill size.

If we go with 140,000 at 3.5" W.C. that is 28,000 per burner that would require a 39 drill size orifice. At 4" W.C. pressure a 41 drill size.

Do not plug any burners as that will cause too much of a cooling affect in the chamber as you will have a loss of radiant transfer.

If you go too far below net rating you will cause the flue gases to drop in temperature which reduces draft and is probably why the flame is somewhat yellow. If you took a CO reading it will also be high I am sure (over 100 PPM air free). The result further up the line is a fixed draft hood bringing in a fixed amount of dilution air which will further cool down the flue gases and reduce draft at the fire.

I agree with Jim Davis that using a vaporstat which is more accurate and running at about 8 ounces is a way to control cycles.

Most important when orifices have been changed is to do a combustion analysis and determine what the equipment is doing.

With steam boilers derating reduces the amount of BTU's required to handle the transistion from 212* water to 212* steam (latent heat of vaporization 975 BTU's per lb of water) The rule it takes 1 BTU to raise the temp of 1 pound of water 1 degree only applys up to 212*. So when we derate a design boiler we may in affect lose much of the BTU required to properly make steam.

Last of all the orifices simply draw a picture of the shape and pull one out and look at the back side and see as close as you can if it is conically shaped or square. As best you can match it up to that.

If you want some further help give me a call at 401-437-0557 be glad to talk to you and help you out.

Unknown

John on the

orifices there is another way. If you have a torch and some solder remove all the orifices and lay them on a non combustible surface after cleaning them with steel wool heat them up and drop some solder in and plug up the existing orifices, then redrill them. When redrilling drill them from the rear and not the front and do them by hand not with a electric drill (too wobbly).

Boiler Guy

Tim is

right on with his advice. In most cases 20% deration is an ABSOLUTE MAXIMUM. You might want to get some written advice from the manufacturer before you take the leap. Derating too much WILL give you trouble.

jim lockard

Make sure

I am not a fan of plugging and redrilling orfices. That said make sure that all of your orfices are the same drill size. Some boiler makers have smaller drill size orfices for the outside burners and larger drill sizes in the center. Use a combustion anyalzer to set everything up. Best Wishes J.Lockard

Unknown

Jim it does require

a little skill. I have been doing it for years when converting to LP and it works fine.

I am just curious which boilers ues differnt orifice sizes for different burners.

jim lockard

Timmie

I ran across a older Burnham steam boiler(360,000 btu) where the outside orfices were smaller then the inside. The boiler had been downfired to the point where it had a hard time heating the home and the gas bill exceeded the mortgage. Now unless someone mixed orfices in this machines history and I questioned the Burnham Rep. he told me that the two outside burners were to be a little downfired. I can not pull up the boiler model # right now Timmie but I will find it. J.Lockard

Mijola

A question for Tim about the orifices

Hi Tim,

Two questions.


#1
Do you have a chart or book that shows the cross reference of the various BTU capacities of LP and Nat gas flow using the different pressures with different orifice sizes? If so, where can I get it?

#2
Wouldn’t it be easier for John to just get a complete new set of orifices of a smaller size than he actually needs for the down fire process, and then just drill them out to the larger size that is calculated to be needed to ultimately down fire the boiler? That way he can keep the old ones unchanged, in case the down fire process is not successful. He can just put the old ones back in, and be up and running quickly. Just a thought.

Best Regards,

Ed Carey

Unknown

Jim the reason I ask you

that was a student of mine said he had run into the same thing on a boiler and he was not sure what brand. I am going to check with Glenn Stanton about that I am curious.

Unknown

Ed if you read his post

he was refused new orifices by the boiler manufacturer so I was trying to give him an alternative quick way to derate.

There are three options we followed at the gas company on reducing orifice sizes:

1. Order new ones, that is the best way to go.

2. The soldering method

3. And this is the one gas men have been using for years, pean over the opening with a ball pean hammer and then redrill. I am sure I will hear from someone on that one.

E-mail me your postal address and I will send you the info on orifices.

Mijola

My e-mail address

Thanks in advance Tim,

Please just pull the address together, no spaces and all small letters. Spacing is an attempt to fool the spam bots.

ea carey hvac

(@) adelphia . net

Best Regards,

Ed Carey

EBEBRATT-Ed

Not my post but Thanks Tim and others

for all the information

bob_44

Altitude

John, call the Mfg. and tell them that you and your boiler are moving to Leadville CO and ask what you should do. That will get you down to 113,021 input. bob

jim lockard

orfice alterations(Timmie)

Timmie --How does the insurance industry feel about alterating burner orfices?. Would this not be a violation of UL or ASRAE or twist someones nose out of joint?.I know that orfices are filled and drilled (jeff foxworthy propane kit) all the time. Thanks J.Lockard

John Lasky

HI Tim some info

thanks for the reply.
here are some answers

1) HB smith GB200

2) bottom is open (5 racks)

3) gas pressure rating 3.5 lb

4)natural gas

5) ive been clocking the gas all winter as Ive been playing with pressure right now im at 118,000 btu sytem is heating fine. stack temp is 246 degrees

6) I did the classic mistake I moved into the house in late october (4 years ago) and found the old boiler had a hole in it so I took the rating off of it and ordered The new one, no questions were asked at the factory and they shipped it . (what do I know im an electrician *G*) thats how It ended up so big.

7) the valve is a honeywell with standing pilot I dont have the # right now but I can get it.

gas usage is about the same as last year but the local utility increased the natural gas rates and the current price per therm is 30% higher than last year OuCH!

I have a seperate gas hot water heater

should I use this boiler for hot water since it probably big enough for 2 jobs???

I was running at rated gas input last year before I started working on everything.


one thing I noticed is at the lower firing rate my system heats much better especially my downstairs which is all burnham baseboards.

at the higher firing rate the baseboards all gurgled, flooded and the vents all hissed and spit water ,lots of water hammer... , at the lower firing rate they all heat nice and even with dry steam and very quiet with no more water hammer.

as far as the orifices go if I do anything Ill have the burner control company I do business with plug and drill them as thats one of the services they do. I can order a set of orifices for my boiler (through the local dist) and have them plugged /drilled and that will give me 2 sets.

like most people Im just trying to get things working the best it can, this all started with a flooded horizontal runout and ive now gone through the whole system , installed main vents added drip lines, repiped plugged return sections ... im now at the boiler.

when at the higher firing rate besides the hissing and spitting I was concerned with the severe short cycle time after I installed the new pressuretrol,

my on time once the system reached cut in was only 2 mins

my off time was about a minute (baseboards condensing fast)

I talked to Ron in the Burnham training dept he advised that a minimum on time should be at least 7 mins.



unfortunatley the boiler is only 4 years old so Id hate to have to scrap it and buy a new one,we also may move in the next 2-3 years dont know if it would be worth it??? is there a used market??

last question, will the vapor stat help my situation? being an electrical controls guy Im sure the presuretrol is not too acurate ill bet my .5 lb cut in is closer to 1LB and cut out is not that acurate either??? will cycle times be longer at 8oz cut out with near 0 cut in ?? it does make some sence to me that my system can go from 2lb - 1 lb pretty fast but to near zero my take longer.


now last thing based on the math on my boiler the EDA is 421 Cubic feet if I drop 20% ill be very close to 321 (336) but the darn system runs lousy at that rate.

but maybe the vaprstat can solve that?


many thanks "John"

Unknown

Jim it is done and

has been done for years. I am probably the most heavily insured individual in the industry. My insurance company when establishing my policy criteria reviewed conversion procedures and others and had no problem with them. I also have this set down in my manuals as a procedure that is a long standing practice in the industry. The biggest problem my insurance company had was the fact that I train Propane personel. That is one big liability, the LP industry has insurance companies standing on their ear just ask anyone in that industry what they pay for liability coverage.

I do not think redrilling or altering orifices to establish correct input presentsa problem. The est way is to order new ones. The problem is on some old equipment you cannot easily find them.

jim lockard

Timmie

I agree with you on drilling and modifying equipment. What I really wanted was your spin on the insurance Co's. Cause as you know there is a lot of old stuff out here and one must do what one must to keep it running. Thanks J.Lockard

Unknown

John it was good

talking to you on the phone. I hope I answered all your questions. For others who may be following this post I will come back and answer Johns questions here later.

Mike T., Swampeast MO

Much of the heat transfer from a burner is radiant(60%)and is the greatest area of transfer. Making the flame smaller in any manner greatly reduces radiant transfer.

Doesn't that directly contradict the newer "radiant" burners that have very little (W/M Ultra) or no (Vitodens) contact between the flame and the HX?

Aren't you greatly reducing conduction with a smaller flame?

Unknown

Mike I do not want to

answer for Jim Davis but I think when we talk about burners atmospheric versus pre-mix it is a very different way of heat transfer.

The modern burner heat exchange is very different from the standard cast iron flame under the heat exchanger which relies heavily on the wiping and radiant heat transfer.

When you can use a flame retention type burner with a zero governor concept and design the burner and its material to hold the flame very close and create direct transfer to the medium with low water content it is a different animal. By placing the coils or water flow system in close proximity to the burner then conduction and convection can become a bigger part of the transfer of heat to the medium.

We all have to be careful when we talk now days as some of us who have been around a long time should disinguish between conventional burner/boiler/furnace design and then 80+ and 90+ burner design.

I am not well versed on the Vitodens burner as I have neglected their invitation to come over and spend a few days with them. I must do that soon they are right near me here in RI. In looking at photos of the burner and its flame it is a very radiant burner to my visual perception.

John Taylor_2

Soldering orifices

Tim, quite some time ago I checked a mobile home furnace that had the orifice soldered and drilled for conversion to propane. The furnace had overfired and I had found that the solder in the orifice had melted and overfired the furnace. The inspection door allowed CO to pour into the home and it almost killed the family that was staying there. I was unable to determine why this occured. The unit had run out of propane just preceeding this and there was some talk that the propane company had overfilled the pig. Have you ever heard of this type of thing happening?

Just Curious,

John Taylor

Unknown

What probably happended

was when the LP tank was running low the flame was flashing back into the burner and caused the solder to melt, it has to get really hot for this to happen however so it is very unusual for that to occur. Then of course if the solder melted the unit is now over fired and makes CO.

Unknown

Tim

I can't say that I have ever seen a mix of different size orifices in our boilers as far back as I can remember. My contact with Burnham products goes back to 1972 and I have not seen this. One of our larger residential steam boilers many years ago had two pilot assemblies and this may be the one Jim is referring to. That was prior to 1972 as far as I remember.

Also, as far as soldering and redrilling orifices goes I will have to take a firm stance against this practice. I have seen it done by those equipped with orifice drills and from a manufacturers standpoint we would have to disagree with this practice for liability reasons. Thanks.

Glenn

Glenn Stanton

Manager of Training

Burnham Hydronics

www.burnham.com

John Taylor_2

Sounds reasonable. I wonder if sil-flos would have suffered the same affect.

John Taylor