Installing a Resister Plate
The over-fire draft should never exceed a -.04 on a flame retention oil burners installed on negative draft boilers. When the 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 the excessive OF draft and the instability of the flame. 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 gauge 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 the pipe.
If the firing rates change on this appliance after the resistor plate is installed, the resistor plate may need to be re-adjusted. Please check with the boiler manufacturer before doing this work to verify that they would agree with this action. A professional installer should perform the installation.
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