Code Classroom
Ron George, CPD President, Plumb-Tech Design & Consulting Services, LLC
I
efficiency water heaters that were installed more than 10 years ago. There were reported problems of not having enough hot water. My inspection revealed a high efficiency water heater
Is PVC an acceptable vent material for flue gases? causes high flue gas temperatures. Most boiler and water heater manufacturers list other ways of venting with stain- less steel, but they seem to always recommend the cheap- est way in their literature, in an attempt to make the boil- er seem more affordable to consumers. The piping manufacturer’s PVC pipe technical manual
recently inspected the mechanical systems in student housing at a Midwest university. The school had hun- dreds of apartments in numerous buildings with high
with purple/brownish PVC pipes and yellowish PVC flue pipe fittings. The flue pipes were obviously deformed from heat, and they were sagging. A maintenance man for the university said that some really bad pipes had come apart at the fittings and melted. This set off the carbon monoxide alarm and prompted a maintenance call. The water heater had scaled up due to minerals in the water supply; this caused the flue gas temperatures to rise, which created the noted problems. The pipe was Schedule 40 PVC pipe. Although the water heater installation manual we obtained recommend-
A family of four died in Aspen, Colorado, in 2008, of carbon monoxide poisoning from the failure of PVC plastic flue pipes
on a condensing snow melting boiler system in a rental property.
ed using PVC pipe as a flue material, PVC pipe manufac- turers do not recommend this. I called the manufacturer of the PVC pipe in this case and asked the representative a few questions about using PVC pipe as a combustion flue for fuel gases. He was quite familiar with this issue and emailed me a link to the company’s technical manual, which discussed all of the physical and temperature limi- tations of the piping. He said that the company has had numerous complaints
about PVC pipes used for venting flue gases, and that they always point out that they do not recommend this usage and that there is no listing for it in their manual. He has asked every major manufacturer of boilers and water heaters for data to support the recommendations in their literature for the use of PVC pipe for combustion flue materials but has not received any replies. This is concerning to me. Just because a manufacturer recommends using PVC does not mean that it is accept- able or safe. Just because PVC works in new installations does not mean that a condition cannot occur in which scale builds up over a short time in hard water areas and
Page 16/Plumbing Engineer
has the following information: Using Plastics for Combustion Gas Venting The piping manufacturer recommends that inquiries
about the suitability of plastic piping systems for venting combustion gases should be directed to the manufacturer of the water or space heating equipment being installed. As stated in the International Code Council’s International Fuel Gas Code 503.4.1.1: Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s installation instructions. Furthermore, several of the ASTM standards applicable
to PVC plastic pipe and fittings that this company manu- factures their pipe to include the following note: This standard specification for PVC pipe does not include requirements for pipe and fittings intended to be used to vent combustion gases. There is no standard referenced in any of the codes in
the United States for a plastic flue vent for combustion flue gas piping, although many water heater and boiler manufacturers recommend this. There is a Canadian stan- dard, ULC S636, but that standard has several flaws in that it allows flue gas temperatures that exceed the tem- perature limits of the pipe material manufacturers. The maximum temperatures listed in the ABS, PVC and
CPVC pipe manufacturers’ technical literature are shown in the following table. Any temperatures above the rated temperature will allow the pipe to melt, sag and, possibly, collapse or pull apart. There are serious consequences with carbon monoxide asphyxiation and fire that cannot be ignored.
Maximum Operating Temperatures for Various Piping Systems
Piping System ABS – Sch. 40
PVC – Sch. 40
CPVC – Copper Tube Size CPVC - Sch. 80
Maximum Operating
Temp - Degrees Fahrenheit 160 F 140 F 180 F 200 F
Generally, for a new condensing water heater or boiler,
the stack temperature will be about 20 degrees higher than the water temperature. The design and efficiency of the unit, along with several other factors, including water quality, will affect the stack temperature. If a water heater is set to store water at 140 F to minimize Legionella bac-
Continued on page 18 May 2011
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72