This article has been printed a few times and it’s always been a very popular piece and answers some questions that constantly come up when doing combustion testing on oil, gas and LP. I like to roll it out every so often since it answers a lot of questions for many people. In addition, after last month’s article it will answer a few questions we got. Many thanks by the way!
The ability to diagnose and repair oil or gas burners seems sometimes out of our control. Regrettably, as these problems have increased, we have not used all of the tools available to us. It is almost impossible today to properly service “state of the art” burners by the ‘let’s eyeball it’ method.
Annoying and costly repeat calls have increased while no one seems to know why. Or do we?
Some companies seem to have fewer problems than others do. Why?
We hope to answer some of these questions here or at least get you to look over how and why you do it ‘your way’. Since almost the beginning of the service industry we have had testing equipment available to us to analyze burner performance.
In the ’70s and ’80s the combustion test kit was used primarily to test ‘steady-state efficiency’ and lost most of its credibility as a true service tool. It is as essential as our flashlight for good burner service.
Since many of us may not have used the kit as often as we should, we will concentrate on reviewing the basics of instrument use and instrument quality.
This material was originally published in The Councilor of the Better Home Heat Council of Massachusetts in 1979 and then in several magazines and stays permanently on my website under an area we call Firedragon Field Notes. It was also published as excerpts in the text, ‘COMBUSTION & Oil Burning Equipment” in 1995-2000 and in Advanced Residential Oilburners since this information never seems to go out of date. Although originally written for oilburners, most of the equipment covered is also used to test gas-fired equipment.
The purpose of this document is, therefore, to eliminate as many discrepancies as possible which come about due to improper care and maintenance of the instruments used in the field. Many servicemen still do not understand the importance and meaning of steady-state test conditions. For their benefit we will re-define the term and discuss the proper use and checkout procedures for these tools.
A condition that exists when the burner has fired long enough to have reached unchanging temperatures. Steady-state is most easily confirmed by the temperature of the flue gas. Steady-state conditions have been reached when there has been no change in temperature for two minutes.
Preparing the unit for testing
It is advised that two holes be made in the stack to speed up testing which is especially important with today’s smaller units, Figure 1. Location of these holes is very important. They should be at least one flue pipe diameter from the draft regulator, dimension A and they should also both be located one to two smoke pipe diameters from the breech, dimension B, excluding all elbows, but always between the breech and draft regulator. By inserting the stack thermometer in one hole, steady state conditions will be proved as soon as possible and leave the other hole for other tests. Another test hole must be located preferably within 12 inches over the fire or in the door closest to fire.
Before performing any tests, the instruments must be checked to insure good test readings:
Checking the dry-type draft gauge – check to be sure that the gauge operates smoothly, Figure 2. By twirling the hose end or by inhaling across tube, a negative pressure should register and then the instrument should return to zero. If it does not return to zero after a couple of samples, the instrument is most likely defective.
Checking the wet-type draft gauge – check to be sure that gauge is level and zeroed.
Check out the same as dry-type gauge. However, if this instrument does not return to zero after a couple of samples, thoroughly clean the instrument and recharge with clean gauge oil.
It has also been found that when draft gauges respond slowly or are sluggish, the following components should be checked: