Background Information - Draft Requirements
Modern boilers operate with higher efficiencies than older boilers. Smaller flueways, as well as bars, pins
and fins are designed into modem boilers to transfer as much heat as possible from the hot gases to the
water or steam and prevent heat loss up the chimney. However, these design features result in higher pres-
sure, or draft loss, in the boiler.
This draft loss must be taken into account when installing an oil boiler into a new or old chimney. New
chimneys are less likely to have poor draft. However, they must have sufficient draft to support combus-
tion. A -.06" draft is desirable and preferred. Older, unlined chimneys may require a replacement liner to
have them perform well enough to support combustion.
An example follows:
Chimney Draft
Old installation New installation
-.04" -.04"
Comments
No change, but older chimneys
(especially unlined ones) have
leaks which reduce draft.
Boiler Design Pressure Drop +.01" +.04"
Required for mandated
efficiency increases.
Draft Over Fire -.03" 0.00"
The old installation would have
had a higher temperature in the
chimney [as high as 800 degrees
vs. 400 degrees F], which would
increase the draft.
The above readings are 'cold' readings [before the boiler and chimney are heated up].
A-.01 _ to -.02" minimum draft over fire is required for a good installation where no oil fumes
would be present. The draft would vent them up the chimney.
The above discussion which concerns draft in the chimney and draft loss in the boiler, is incomplete with-
out discussing the effect of draft on the burner. Very simply, increasing the fuel usage [higher gallonage] on
a unit which has multiple firing rates, requires more air for combustion and a higher draft loss in the boiler.
As an example, increasing the firing rate 1/4 gallon will increase the draft loss in the unit by approximately
+.01". The actual burner used on a particular boiler also effects the draft and smoke condition. The use of
a burner supplied by Peerless Heater Company wouM assure you of a quality, trouble free installation.
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