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vent cap.
4. Blockage. Check the system for blockage by removing the cap, and
looking down into the vent with a flashlight. Check for bird nests, debris,
rodents, insects, or other obstructions. If nothing is found, inspect the entire
systemforphysicaldamage.
5.Downdraft. Downdraftsaregenerallycausedbythesystem'stermination
beingtooclosetoanadjacentwall,parapet,orotherstructure. Ifthecapiswithin
eightfeetofsuchanobstruction,itmustalsobeatleasttwofeetaboveit. Alsoinsure
thatthetopisattheheightprescribedforyourroofpitchinTable2. Inadequate
combustionair isalso amajor causeof downdraftproblems. Appliances like
clothesdryersorotherexhaustingappliancesinthesameutilityroomcancause
downdraftproblems.
6. Condensate/Corrosion. Continuouscondensate can cause corrosion
(rusting)ofvents,tops,appliancedrafthoods,andothercomponentsofthesystem,
as well as the inside of the appliance. This situation can be extremely
dangerous, and corrective action must be taken immediately.Common
causesofcorrosionarelistedbelow: Ifindoubtcallaprofessionaltoinspectthe
vent. (a) Iftheventsystemislocatedinanareawherespraycansorsolventsare
usedextensively,(laundryareas,orpaintshops,forexample),thehalogenated
compounds get into the combustion air. When they are burned, they form
compoundsthatcausecorrosion. Thecorrectiveactioninthiscase,istoisolatethe
appliance,andgettheairsupplyfromoutside,oranuncontaminatedarea.
(b) Condensatemaybecaused byincorrectsizing of theventsystem.
Followtheproceduresinthevarioussizingpublications toobtainthecorrectsizes
for connectors and vents. Other causes are: excessive lateral runs, too many
elbows,coldatticsandcrawlspaces,andlargeareasoftheexteriorportionsofthe
ventingsystemexposedtocoldweather. Asageneralrule,lateralsshouldbeheld
toaminimum,andbe nolongerthan75%of theverticalheightofthe system.
Condensatemay initiallyappearasbeadsontheoutsideoftheconnectororvent.
7. Construction. Laterals, offsets, and vertical components should be
securelysupportedwithwallstraps,aspreviouslydescribed. Componentsof
theventwhichareinoccupiedareasshouldbeenclosedtopreventaccidental
contactanddamagetotheventsystem. Insurethatinsulation,buildingmaterials,
or debris do not extend into the required clearance spaces. In cold climates,
theexteriorportionsoftheventshouldbeenclosedinachase. Outsideportions
of the vent system with may be painted with high temperature paint to help