Installing a Resister Plate

Here is a way of temporarily reducing the excessive over-fire (OF) draft on an oil-fired boiler
The proper way to reduce the draft is install a properly sized stainless steel chimney liner.

The over-fire draft should never exceed a -.04 on a flame retention oil burners installed on negative draft boilers. When draft is excessive the flame becomes unstable and may start bouncing off the combustion head and usually becomes noisier. This condition can create soot and head carbon build-up. The amount of soot is caused by how excessive the OF draft is and how unstable the flame becomes. On pressure fired equipment the reading should be done at the breach of the appliance. Many of these units the breech draft should be "0" and not over -0.03" w.c.

Refer to manufacturers I&O manuals for proper draft readings.

1. Close the draft regulator so it is just barely open. I say about 1/4". Verify the draft regulator is at least 18" from the boiler, further is better.
2. Cut a slot in the vent pipe approximately 12" above the boiler and about 1/2 way around the pipe with a fine hacksaw blade

3. Cut a piece of tin to fit into the slot and cut the corners off so it matches the curvature of the pipe better.

4. Insert the draft gage into the appliance to obtain the proper OF draft.
5. Slide the tin in until you get a -0.01 to -0.02  draft on the meter. Check I&O manual.
6. Mark the tin at the vent pipe.

7. Pull out the tin and cut off the excess tin leaving about 3/4" above the line to bend tabs for fastening.

8. Cut the tabs bending every other tab up or down.
9. Screw two tabs to pipe.

If the firing rates changes on this appliance after the resister plate is installed the resister plate may need to be re-adjusted. Please check with boiler manufacturer before doing this work to verify they would agree with this action. The installation should be performed by a professional installer.

Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, installations should be reviewed on a per job situation. Any work performed on your heating system should be performed by qualified and experienced personnel only. Comfort-Calc or its personnel accepts no responsibility for improper information, application, damage to property or bodily injury from applied information found on this website as it should be reviewed by a professional.