Oil burner smoke test example (C) Daniel FriedmanOil Burner Tests & Adjustments
How to Measure & Set Oil Burner Combustion Air & Smoke Levels

  • OIL BURNER SMOKE TEST - CONTENTS: Guide to oil burner operating tests: Bachrach or Bosch Smoke Numbers. How to measure oil burner smoke level to evaluate system efficiency and operation. What is the correct smoke level for oil burners. What is the proper air shutter adjustment position on an oil burner? How to Diagnose Oil Burner Noise, Smoke, Odors. Diagnose & repair oil burner soot, puffback, rumbling, hard-starting.
  • POST a QUESTION or READ FAQs about oil burner performance tests and measurements
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Oil burner smoke test which in turn reflects combustion air & temperature adjustment are necessary for safe, efficient and reliable oil burner operation: this article explains and illustrates oil burner smoke testing - a key step in oil burner adjustment for proper operation.

An oil burner flame that is too smoky soots-up the heating system leading ultimately to a no-heat call and a clogged furnace or boiler or water heater. An oil burner flame that "looks very clean" may in fact be running too hot, wasting fuel, increasing heating costs, damaging equipment, or perhaps even unsafe. This article describes how we measure the oil burner smoke level and describes the proper smoke settings.

This article series answers most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.

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Oil Burner Smoke Test - Indicates Proper Combustion Air, Draft, Burner Adjustment

Oil burner smoke test equipment, Bachrach Kit (C) Daniel FriedmanIf the oil burner is not working, start your diagnosis at OIL BURNER INSPECTION & REPAIR.

The basic measurements made by any competent oil heat service technician include the stack temperature, draft, smoke level, and carbon dioxide level (OIL BURNER CO2 TEST).

These data tell us whether or not the equipment is properly adjusted and operating safely and economically. Here we explain how we measure the Bachrach or Bosch smoke numbers - a slightly subjective evaluation of the level of smoke or "soot" found in oil burner exhaust flues.

One of these most basic tests performed by an oil heat service technician is the "smoke test" using a strip of filter paper and a pump to sample the oil burner exhaust, measuring the level of smoke in the exhaust. In fact once an oil burner has been installed or just after the oil burner has been serviced, the service technician will usually start her system tuning and adjustment with a simple smoke test.

Our photo (left) shows a traditional smoke testing pump (the black cylinder with a handle at its right end) used for decades. This equipment was produced by Bachrach, an oil burner test equipment manufacturer.

Steps in Conducting an Oil Burner Smoke Level Test

  1. The technician allows the oil burner to reach normal operating temperature (perhaps after it has been on for five minutes),
  2. A clean white strip of filter paper is inserted into the end of the smoke testing pump.
  3. The nozzle of the smoke tester is inserted into a 1/4" diameter hole in the flue vent connector pipe, typically just a few inches above the top of the oil-fired heating boiler or furnace.
  4. The pump is operated
  5. The filter strip is removed and the "blackness" of the sample spot is compared with a scale that rates the soot level. An experienced oil heat service technician simply looks at the black or gray spot on the filter paper.

    Watch out: as we have written in several articles, it is impossible to do a good job cleaning and servicing oil fired heating equipment without getting dirty.

    But if you put your sooty fingers all over the filter paper before or after conducting a Bachrach / Bosch smoke test, then soot from your hands will get onto the filter paper and you may mistake a 0 smoke reading as a 1 or 2 level smoke. Don't touch the smoke sample test area with your dirty fingers.

Oil burner smoke test example (C) Daniel FriedmanZero-level smoke in a Bachrach / Bosch test is actually "too clean" for most oil burners, and means that there is too much air entering the oil burner, causing the burner to operate too hot, and sending too much heat (and thus the money the homeowner spent on heating oil) up the chimney.

The correct smoke level is just a "trace" of smoke on the filter paper, a level of 1 is good.

A smoke level of "1" or "2" is normal. In our oil burner smoke test results photo (at left) you can see four smoke test samples. Sample #1 is certainly too dirty, sample #2 and sample #3 are a bit high, though we might accept sample #3. Sample #4 is just slightly above zero and is a good setting.

Watch out: sorry for the labels in our photo at left: Don't mix up our sample numbers #1 - 4 with smoke level values = 0,1,2,3, etc. A smoke level of 0 means there is no black soot visible on the filter paper.

The Bachrach or Bosch smoke number scale ranges from 0 (no detected smoke) to 9 (solid black). In addition to using the hand operated smoke pump illustrated here, some electronic combustion analyzers can also produce a smoke level number. [Click any image or table to see an enlarged, detailed version.]

Higher smoke levels indicate that the system is operating too "dirty" or smoky. High levels of soot in the oil burner exhaust mean that the system will deposit soot more rapidly inside of the furnace or boiler heat exchanger, interfering with heat transfer into the building heating air or water, and thus increasing system operating cost - meaning higher heating bills and more frequent oil burner service needed.

Very high smoke levels may indicate or even cause plugging up of the furnace or boiler, leading to improper oil burner operation, an unsafe system, and possibly other malfunctions, even a "puffback".

Should we Set The Oil Burner for Zero Smoke?

Setting an oil burner to zero smoke (C) D FriedmanTo perform the oil burner "smoke" adjustment correctly and to avoid over-firing or overheating the boiler, as well as to avoid an inefficient set-up that sends too much heat up the chimney, the heating service tech will first set the oil burner for just a trace of smoke (#1 in our photo at left), then s/he will slightly increase combustion air until the trace just vanishes to a zero smoke reading (#2 and #3 in our photo) with the test filter paper and smoke gun.

Technical note: on some modern oil fired heating systems the oil burner combustion air and oil pressure are adjusted to a standard of zero smoke rather than a trace of smoke.

Watch out: Other measurements including stack temperature, draft, and CO2 are required to properly and safely set up an oil burner.

Watch out: Don't come at zero smoke from a position of too much combustion air or you won't know what you've got and you may be wasting fuel and overheating the equipment. Thanks to Bob, a heating service technician at Bottini Oil, for this service tip.

Also see COMPLETE COMBUSTION, STOICHIOMETRIC for an explanation of complete fuel combustion and boiler or furnace maximum efficiency.

Oil Burner Smoke Number Standards

While technicians and equipment suppliers commonly refer to a Bachrach smoke number or Bosch smoke number, these smoke measurements are also standardized in ISO 10054

Actually there are at least eleven different smoke level measurement standards. Homan (1985) reports on standardization among these.[5]

The second common test performed by an oil heat technician evaluates the oil burner efficiency by measuring the carbon dioxide level or CO2 level in the oil burner exhaust.

Details of measuring the carbon dioxide level for oil burners, a second key measurement needed for proper setting of oil burner combustion air & operating temperature are now at OIL BURNER CO2 TEST

Combustion Analyzer Recommendations & Sources of Oil or Gas Burner Combustion Testing Kits include Oil Burner Smoke Level Measuring Devices

Also see COMPLETE COMBUSTION, STOICHIOMETRIC for an explanation of complete fuel combustion and boiler or furnace maximum efficiency.

How does the oil burner tech adjust the Air Shutter on an Oil Burner? Combustion air adjustment procedure.

Beckett oil burner air shutter adjustment (C) Daniel Friedman"Set the oil burner smoke level" as we mention in the article above at OIL BURNER SMOKE TEST, means that the service technician will have to adjust one or more of the following in order to obtain the desired trace of smoke on the smoke test or zero smoke + a specified operating temperature range if that alterative is called for by the oil burner manufacturer.

At left you can see that the pointer on the air shutter on this Beckett Model AF oil burner is set to an index number of 3 1/2. The oil burner is sensitive to small changes in intake air. At that 3 1/2 setting you can just barely see an air opening at the top and bottom of the large shutter openings - those two small black areas.

[Click to enlarge any image].

The air intake shutter at the oil burner is adjusted by loosening one or two clamping screws, then rotating the air shutter to a higher index position to increase or to a lower index number to decrease the rate of air flow into the oil burner. This adjustment is made first, then the technician measures either O2 or CO2 to make further adjustments.

Most newer oil burners such as the Beckett™ series include index marks along the side of the oil burner body and a pointer attached to the oil burner air shutter. There may also be a label affixed to the oil burner OR a table in the oil burner's instruction manual that suggests a recommended intake air shutter position for various oil burner nozzle sizes (in GPH).

Beckett recommends that after you've set the oil burner to give just a trace of smoke using a smoke tester, then you open the air shutter until this level changes (from a presumed slightly higher measurement) down to 12.0% CO2 or 4.5% O2. That gives an efficient and seasonally-clean oil burner operation with a slight safety margin without overheating the system.

Watch out: particularly with newer high-speed, higher efficiency oil burners, if there are other air leaks such as around the transformer at the upper rear of the oil burner assembly you may have trouble setting and regulating the desired burner intake air rate. Be sure that the plate mating the transformer to the oil burner top is flat, not bent, and remember to tighten the screws that hold the hinged-type transformer front end down snugly in place.

Fyrite combustion analyzer (C) Watch out: while back in the "old days" it was reasonable to "tune" an low speed (1725 RPM) oil burner by eye with a bit of spit and guesswork, that is not the case with modern, high speed (3450 RPM) oil burners. In fact the flame may not even be visible, and spitting on the flue vent connector is no longer an adequate measure of temperature, nor of CO2. Instead the oil heat service technician must make use of instruments to measure draft, temperature, CO2 or O2 as well as smoke level.

Placement of the stack temperature measuring thermomster probe (C)

Watch out: direct-vent oil fired heating equipment will not use a conventional chimney nor barometric damper, but the combustion air, air shutter, and other oil burner adjustments are still required for proper and safe operation.


Smoke Tests, Smoke Numbers, Smoke Testing Equipment for Heating Systems

Bosch smoke meter equipment, Dabill, UK

The articles at this website describe how to recognize common oil-fired heating appliance operating or safety defects, and how to save money on home heating costs.


Continue reading at OIL BURNER CO2 TEST or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see OIL HEAT TEXTBOOK - free online textbook

Or see HEATING SYSTEM INSPECTION PROCEDURE an organized approach to inspecting the entire heating system, beginning outdoors, continuing indoors, and ultimately in most detail in the boiler or furnace room.


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