Thermo Products PGL20-180, PGT16-160, PGT5-100, PGT11-125 Vent Dampers, Condensing in the Chimney

All installations and services must be performed by qualified service personnel.

NOTE: If this furnace replaces an appliance with a vent that was originally installed in a common vent system serving other appliances, the vent system is likely now too large to properly vent the remaining appliances only and must be modified accordingly. Refer to Natural Fuel Gas Code Appendix G Category I vent tables for common venting a PG Series furnace and another fan assisted or natural draft unit.

In order too common vent a PG Series furnace with a natural draft gas fired hot water heater; follow the recommendation of the NFGC Category I venting tables.

If the NFGC venting tables do not apply to a specific common venting system then refer to the section on replacing an existing furnace from a common vent in Section G of this manual.

NOTICE: Thermo Pride power gas units may be sidewall vented with a power sidewall venting system that is appropriate for the application and certified by a nationally recognized testing agency for use with gas fired warm air central furnaces.

NOTICE: An agency approved gas barometric control or draft diverter must be installed. The draft control device must also meet the approval of the local authorities. See the draft control manufacturers instructions for installation.

E. VENT DAMPERS

If a vent damper is installed, it must be certified by a nationally recognized testing agency. It must be an electro- mechanical type that opens completely before gas flows to the main burner and closes only after the gas valve has shut off gas flow to the main burner.

WARNING: The PG Series furnaces must not be installed with a manual or thermally actuated vent damper.

F. CONDENSING IN THE CHIMNEY:

Due to the increasing efficiencies of our furnaces, more heat is being placed into the home instead of up the chimney. This means that the stack temperature will be lowered which may result in condensing within the chimney under certain conditions. The following is an explanation on why and what to do if condensing occurs.

Moisture occurs in flue gases when hydrogen is mixed with oxygen from the chemical reaction produced by combustion. This mixture of hydrogen and oxygen produces water molecules.

The flue gas vapor may do one of two things as it escapes up the chimney:

1.Remain in a vapor state if the internal chimney wall temperature is above the dew point, or

2.Condense on the chimney walls if they are chilled below the dew point.

Condensing will always occur on chimney walls whose temperatures are below the dew point, but will evaporate once the walls are warmer than the dew point. If the chimney walls do not reach the dew point during the cycle of the furnace, the moisture may accumulate in large enough quantities to cause problems such as corrosion of the chimney or corrosion of the heat exchanger.

This condensation most likely will not occur at the bottom of the chimney, because the flue gas is heating the chimney walls as it rises and the bottom will be heated first. This heating of the walls will cause the flue gas temperature to drop, which in turn may reduce the wall temperature below the dew point causing condensation to appear on the upper part of the chimney first. This condensation may drip back as far as the flue pipe and heat exchanger, where corrosion may occur if not treated.

To prevent condensation, it is necessary that the internal chimney wall temperature always be kept above the dew point. The chimney may have to be lined with a flue liner if the temperature loss is too great for the furnace. A liner will act as an insulator and reduce the flue gas temperature loss. Insulation may be added around the liner for further

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