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5
II. GENERAL INSTRUCTIONS
A. VENTING:
The OHC furnace venting system must be installed by a qualified service person in accordance with
local installation codes and these instructions. In the absence of applicable local codes, conform to the
National Fuel Gas Code, NFPA 54/ANSI Z223.1 or latest edition.
Installation shall, at least, conform to the following requirements.
1. The exhaust vent/combustion air intake termination specified by Thermo Products, in this
manual, shall be used.
2. All plastic pipe and pipefittings sourced to complete the exhaust vent and air intake
systems shall be constructed of rigid PVC (polyvinyl chloride) plastic. All components
shall have a wall thickness equivalent to Schedule 40 series materials.
In addition, all sourced PVC components shall be listed by a nationally recognized testing
agency (e.g. NSF, UL, etc.) as conforming to one (1) or more of the following design standard.
PVC Pipe Designation Design Standard
DWV ( Drain-Waste-Vent) ASTM-D2665
Schedule 40 ASTM-D1785
3. The exhaust vent pipe and combustion air pipe shall be at least as large as the exhaust vent/
air intake pipe specified by Thermo Products. Size reduction is never permissible. The
required exhaust vent/ air intake pipe size is 3”.
4. The furnace model series OHC shall not be common vented with any other appliance,
including those burning solid fuels.
5. All horizontal runs of exhaust vent pipe shall slope upward at least ¼ inch per foot from the
outlet of the furnace to the venter connection. This slope will permit proper drainage of the
condensate.
6. The exhaust vent pipe shall be supported at every joint ( no more than 4-feet between
supports) to prevent pipe blockage due to condensate trapped at a local low point, or sag,
in the vent system.
7. The maximum permissible length of piping (consisting of a combination of straight pipe
and a corresponding number of elbows) permitted is: (Each elbow equals 5 ‘ of straight pipe).
• 55 equivalent feet, for the exhaust vent system,( eg. 25’ of straight pipe & 6 elbows)
•
65 equivalent feet, for the combustion air intake system, (eg. 35’ of straight pipe &
5 elbows).
8. When counting pipe elbows, all elbows used in the exhaust
vent or combustion air intake systems must be considered. This includes all elbows, or
equivalent pipefittings, used inside the furnace jacket. Allow 5’ for each elbow.
Note: Two (2), 45
0
elbows can be substituted for one (1), 90
0
elbow.