Oil boiler with gas conversion burner

STEAM DOCTOR

Good morning to all. Looking to install my first new steam gas boiler using an oil boiler with a conversion gas burner. What are the estimated efficiencies comparing a standard atmospheric gas boiler to a standard oil boiler with gas burner to a triple pass oil boiler with gas burner? There is a substantial difference in price between the triple pass boilers and the standard oil boilers. I want to be able to give my customer all the options. Thank you.

STEAM DOCTOR

Standard vs triple pass

I have people whispering(or shouting in some cases) in my ear, that conversion burners are only more efficient if used with triple pass boilers. However, a standard atmospheric gas boiler is more efficient than a standard oil boil with a conversion burner.



True or false???



Thank you.

nicholas bonham-carter

Atmospheric or forced draft burner?

In spite of the most careful measurements of the radiation EDR there can be some over sizing or under sizing of the boiler. The atmospheric boiler will not be so easily matched to the load, without a 2--stage gas valve, which is an additional but worthwhile expense. Alternatively, a tag-team of atmospherics can be installed. A pair of smaller boilers may be easier to install, if there is space. Proper controls will only fire both of them at lower pressures (2 ounces), then drop the lag boiler out to maintain the lower pressure.

The gas burner can be tuned through a fairly wide range of BTU outputs to find the sweet spot, which translates to higher efficiency. This efficiency can be demonstrated to the customer, with the mandatory combustion analysis performed at the end of the installation.--NBC

The atmospheric boiler is very quiet, whereas the triple pas boiler, and gas gun can be noisier.--NBC

Steamhead

Thermal Efficiency

is the difference. This is expressed as the DOE output (Gross output on larger boilers) in BTU per hour, as a percentage of the Input BTU per hour.



When doing this calculation on a standard calculator, for a boiler having an Input of 187,000 BTUH and a DOE Output of 152,000 BTUH, you would enter 152,000 divided by 187,000 but instead of hitting the = key, you'd hit %. The result here would be 81.28.



Atmospheric steam boilers typically run 80-81% thermal efficiency. Most of this is due to the higher excess air in the combustion process (typically 35-50% as opposed to 25% or less with a power burner, which lets more heat go up the chimney) as well as heat losses from the base, which does not have water moving thru it to absorb heat. DOE does not consider base losses as "losses", since the heat is released in the space around the boiler, but since this heat invariably warms the combustion air and eventually goes up the chimney, we want to eliminate it. We want that heat to go to the radiators.



We find thermal efficiencies of 85-86% on wet-base steam boilers with power burners, because they eliminate those two inefficiencies.



Thermal efficiency is often overlooked since most people are stuck on AFUE, but it plays an important part of the boiler's over-all efficiency.

JStar

Boilers

As far as I know, there is not yet a 3-pass steam boiler that is approved for use with natural gas. That means no warranty coverage. However, this wouldn't stop me from doing it in my own home. It will run great and last a long time if properly maintained.



If you ever want any field-assistance with the fine-tuning and setup, I'm not that far from you!

STEAM DOCTOR

Just to confirm

Steamhead. The efficiency numbers you are talking about are on a triple pass boiler or a non triple pass converted oil boiler?



Jstar. I might take you up on your offer. I also need to talk with you at some point about hi/lo firing steam boilers.



Thank you.

Steamhead

They are

for either type. Use the factory-published ratings. Multiply the oil firing rate by 140,000 to get the Input BTUH. 

j a_2

Eguipment

What appliances are you using? Boiler manufacture ,combined with what manufacture conversion burner? Inside or outside chimney? Existing gas pressure?….

Steamhead

Mostly

Slant/Fin Intrepid and Columbia CSFE for the smaller jobs, with one or two Weil-McLain SGO when we needed to disassemble the block to bring it in. Mostly W-M 80 series for light commercial jobs, with a couple Burnham V9A. Which one we choose is based on the specifics of the particular job.



Most of our burners are Carlin (EZ-Gas, 201Gas, 301Gas) though we have used some Midco and PowerFlame units.



Most of our chimneys are semi-exposed, and the owners have them lined.



Almost all our gas services are low-pressure, 7-8" w.c.