Category iii appliances in residential use are mostly tank less water heaters that are vented through the wall with stainless steel.
Category 3 appliance venting.
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Use only pressurizable vent as specified by manufacturer.
Venting listed category i gas fired appliances listed appliances equipped with a draft hood and appliances listed for use with type b gas vents are 1 factory built chimneys 2 listed chimney lining systems for gas venting in masonry chimneys and 3 type b gas vents.
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Category iii is defined as a gas heating appliance with a flue loss equal or greater than 17 non condensing with a positive vent static pressure.
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In a category iii venting system if there is a.
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Newer ul standards however only permit the use of specialized category iii appliance vent material for residential installations that are sidewall vented.
Refer to figure 2.
Category iii refers to positive vent pressure which is created by exhaust blowers in unit heaters.
In short it is a us standard for gas venting systems required in category iii applications.
Use only special condensing service vent as specified by manufacturer.
Chapter 13 sizing of category i venting systems vent connectors slope in ft upward to chimney vent not smaller than appliance flue up to 2 sizes larger than appliance flue length depends on type for single appliance single wall 75 of vent height b vent 100 of vent height 18 inch diameter for multiple appliances 34.
This stuff is gastight stainless steel and hideously expensive.
When venting two appliances separately into a common chimney always install the smaller flue pipe appliance with lowest gph input at a higher point into the chimney than the larger flue pipe for the appliance with the largest gph input.
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