The answer is YES and NO! An 80% efficient furnace CAN be side wall vented per National Fuel as Code 7.3.4 with the use of a “mechanical draft system of either forced or induced draft design”.
So what does this mean? You CANNOT just take the vent off an 80% efficient furnace and run it out a side wall. You need to use an auxiliary power inducer. Both Field Control and Tjernlund make these kits.Which ever you choose to use, it must include the following features:
- a pressure switch, in order to prove the inducer is operating before allowing the furnace to operate.
- A barometric damper must be included, this is necessary for 2 reasons:
- The combustion air flow through the furnace must be controlled or its efficiency will decline. The barometric damper will prevent pulling additional excess air through the furnace.
- The other reason for installing the barometric damper is to allow dilution air to be pulled into the vent. This additional air helps prevent condensation from forming in the B-Vent.
- The entire vent system must be run in B-Vent from the furnace outlet to the side wall induced draft fan.
- An inducer post purge cycle must also be included to allow venting of all the products of combustion at the end of the heating cycle.
In applying auxiliary power inducers be sure that these 4 features are included and exactly follow the manufacturer’s application and installation instructions.
In a lot of case, where a vertical vent is not possible, the use of the side wall auxiliary kit will work. Also, keep in mind, that all 90+% efficient furnace can be side wall vented with just PVC pipe and the need for all of the above is not necessary. In some cases, it is more economical to upgrade to a 90+% efficient furnace than to add all of the equipment and B-vent needed to side wall vent an 80% efficient furnace.
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