For Plumbers & Contractors Training Information Technical Documents Discussion Forums   Forum  General Discuss...  Installations  Sealing Wall Penetrations   Previous   Next    4/1/2008 5:16 PM    rickmanier 0 posts Sealing Wall Penetrations  I went on a service call last week on a GWH635ES that had frozen, while located in a crawl space adjacent to a large, open basement that was at 65 degrees or so. The issue was how the annulus around the vent and combustion air inlet was sealed (NOT!). While this job had about 1/2" gap all around both pipes, I can see using something like "Great Stuff" foam for the inlet, but what are your specific recommendations for the vent? The contractor felt that this was a design defect on Bosch's part, but I asked him where the freezing source was... I look forward to your response, and to your 4/15-16 school!  4/2/2008 7:10 AM    brucerowe 2 posts RE: Sealing Wall Penetrations  There are a number of different issues that can cause frozen heaters. The most common is cold air being drawn through a heater on a very cold night. The exhaust and intake pipes must be sealed air-tight and penetrate through the same wall (at least 3' between terminations). If not, a pressure differential could be created that would draw the cold air through the heater, freezing the pipes or heat exchanger. If the combustion air comes from inside the building, other appliances in the building could draw air from outside through the heater and freeze it. If there are air gaps around the exhaust thimble or intake pipes, cold air could be drawn in also. Those gaps could be sealed with polyisocyanurate or polyurethane foam or caulk; however the gap between the exhaust pipe and thimble should be sealed with RTV high temperature silicone sealant. If the heater is mounted on a very cold wall, it could also cause the heater to freeze. Installation of the freeze prevention kit (part number 7709003574) may help in some situations.  Page 1 of 1   Previous   Next     Forum  General Discuss...  Installations  Sealing Wall Penetrations Register | Login