Overgassed boilers!!!

Ron Beck

Timmie while I totally agree with your posts I was just adding the part or the draft hood as the height is very inportant. While it does divert down drafts and venting the boiler even without the chimney. The chimney or power venter nood only eleiminant the products of combustion. I agree with every point you made. I was stressing the issure of while installing the draft hood it may not be altered in any way as the height of the diverter from the boiler is critical in pulling enough secondary air across the burners to establish good combustion. If the height of the draft hood is lowered and less secondary air is pulled across the burners the CO will increase and depending on the distance it was lowered may even cause a lazy fire. If it is increased it will increase stack temp and reduce efficency and in extreme cases cause the flame to burn in the heat exchanger. The secondary issue in draft hood height is reducing the temperature which flue gas condensation occurs. The height of the draft hood is part of the certification of the boiler and may not be altered in height or application to the boiler. One may not use someone elses or an after market draft hood which I am sure you are completly aware of.
When I responded to you post I was just complimenting you info with alittle more. Keep up the great work you do for the industry.

Unknown

Am I missing something

Just had the second boiler today with the same problem created by the same service person. Here it is:

A four burner boiler make not important, BTU input is 96,000 BTU's, rating plate calls for 3.5" W.C. gas pressure (Natural Gas) to the best of my knowledge it came with air shutters on the four burners (found them on a shelf). The drill size for each burner was a 42 Drill Size which at 3.5" will give about 96,000 or close to it.

When I clocked the burners it was burning 128,000 BTU's.
The customer was upset because this is the third time they have had to have the boiler cleaned it keeps carboning up.

By the way I had another similar situation about a week ago on another boiler.

I found that the service person (same person both jobs) had screwed the regulator all the way down I got 5.1" W.C. with my gauge. This is a valve with a built in servo pressure regulator. One was a Honeywell valve the other a Robertshaw valve.

The service technician who did this advised me that he was instructed at a class on Carbon Monoxide safety to remove the air shutters on a designed natural gas systems and screw the regulator all the way down to prevent carbon monoxide build up. I found with the boiler running after the boiler was cleaned 750 ppm in the flue before the draft hood.

We recleaned the boiler, reset the regulator to 3.5" W.C. and found the air shutters and put them back, also found insufficient air into this boiler room, the technician I was with on the job (not the same one who did this to the boiler) is going back tomorrow and going to cut in some air openings.

We retested CO2 8.5% - O2 6.5% - Net stack 425 degrees (F) for 78% efficiency. Ran the boiler all day today and went back at 5:00 pm today and rechecked CO in the flue is now 25 PPM. We have a draft of -.02" W.C.

Now am I missing something here, I have heard this several times in recent months about screwing down on regulators and throwing away air shutters. In my 40 years in this business I never heard of this before. I would think that boiler and furnace manufacturers who have put their equipment through testing labs for approval would have a real problem with this.

As always I am open to learn, if anyone knows what this is all about please educate me. By the way that service tech who is doing this has done it to every job he has started and checked this past 14 months. I am trying to find an answer to this as I said this is not the first time I have heard this. I advised this young man, very polite and wanting to learn I might say, to go back and put every job back the way it was.

Unknown

Timmie

You're right.

Manufacturers have a problem with that.

Let me know if I can help back you on this.

Noel

Steamhead

In my neck of the woods

I see a lot of wide-open air shutters, but have never seen the regulators screwed down. I hope whoever has been teaching this never comes to Baltimore.

Yes, a good digital tester isn't cheap, but there's no other way to do the job right.

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Glen

misleading instructions?

There are some gas valves which are supplied with initial setup instructions, eg screw down the pressure reg adjustment screw 13 turns, etc. This I have done over the years - and then attach the magnehelix - only to back out the same screw 3 or 4 turns. The point is this - set the output to the appliance rating plate g, 3 inches, 3.5 inches etc, - this is a maximum manifold pressure, clock the appliance, use a good combustion analyser, check draft, do all the good things that our training & small voices in our brains tell us to do. All these numbers and bits of data are for our benefit - and at the end of the day - the darn thing works as well as it should. This doesn't happen by accident - read the Firedragons discourse on combustion analysis - it applies to gas as well. Apologize for the rant - not all instructions are to be obeyed verbatim. And take that technician aside and teach him/her some good on the job basics ...

Ron Beck

Overgassing

The gas pressure should alsways be adjusted to the manufacturer spec's then clock (natural gas) the meter. You may never overfired the boiler, and in fact underfire the boiler by more than 2% with factory supplied orifices. The input may never exceed the rating plate. If the product is a natural draft product the draft hood is designed to pull excess secondary air over the burners, if they are over firing you will not get enough secondary air for good, safe, clean combustion. Another point is adjusting gas pressure to spec does not mean the unit is not overfired. You Must clock the meter to verify this.
Just my 2 cents worth.

Unknown

What gas valves are these?

I have been in this business a long time never run into this?????

I can not convince this technician that he needs training, he spent $600 and three days in training to learn to do this. He feels that the people who taught him this are nationally recognzed as experts and know a lot more than I do about gas combustion.

Unknown

What gas valves are these?

I have been in this business a long time never run into this?????

Unknown

Draft Hood designed

to pull excess secondary air over the burner. I am not sure if that makes sense, excessive excess air reduces efficiency. I thought the draft hood was to :

1. Provide for the ready escape of the flue gases from the appliance in the event of no draft, back draft or stoppage beyond the draft hood.

2. Prevent backdraft from entering the appliance

3. And probably most important, neutralize the effect of stack action of the chimney or gas vent upon the operation of the appliance.

Secondary air is controlled by the design of the equipment on factory designed natural gas systems. The only time you adjust secondary air as pertaining to natural gas is on gas conversion burners.

Dale

Another good reason

for the draft hood on gas designed equipment is to keep flue temp low enough for B Vent. I still like the old dillution air opening description to remind me what else the draft hood does. I wondered why mobile home furnaces don't use B Vent and was told by Miller many year ago that their product could go to 900 degrees flue temp under worse case. Education is so important in our trade, keep up the good work you guys.

Unknown

An old timer by the name of

Thomas Kincaid taught us all that if you can not get rise on a flue pipe connection increase one size. I am often asked why boilers come with the draft hood at a fixed height. (That is what Ron Beck is talking about). That is so that with that amount of rise before you get to the draft hood you insure what is often called the self venting aspect of a guaranteed height off the top of the boiler or any other equipment. And Ron is corect that rise will affect draft which in turn will affect air for combustion (secondary air). In fact if you look at the tables and charts for natural draft venting in the code book they only go up to a rise of 3 feet. The reason they do not go any higher is anything over three feet is considered self venting. It is obviously a little difficult most of the time to get much more that three feet anyway. Thanks Ron