3" b-vent dovetails into 4" single wall right at the ceiling line. the 4" was capped off after it penetrated the roof. total length of venting is 8 feet
eventually the 4" single wall corroded to the point it split open, which then dumped the product of combustion into the attic area.
could the non-vented water heater cause water hammer?
No - that's probably the death throws of the occupants (including animal life in the roof) Re the water hammer - lots of times the bracketing works loose or external pipe insulation shrinks back over time, or someone buys an appliance which has solenoid water controls (like a washing machine) - check out the brackets(should be one every metre/3ft or so), insulation and if it's an appliance causing it - fit a water hammer arrester (pipe piece with a diaphram & spring). As for the venting - no wonder it corroded through!!! It's possibly marginally safer now that it's venting to the roof than when the flue was capped and the carbon monoxide and nitros oxide was being vented at the heater itself - but this NEEDS to flued to outside properly.
Speaking of hot water - we've had people in commercial and medical buildings who thought that rather than fit thermostatic mixing valves, they'd reduce the hot water temperature at the heating unit from 70degC/160degF to about
50degC/120degF and after a few incidents of legionnella (showers & spa baths) they looked up the Standards and found that the building hot water supply must retain the capability of delivering 60degC/140degF water at the most disadvantaged hot water outlet and this must occur within 60 seconds of opening the hot water supply c*ck (you need 60degC/140degF hot water to provide an effective kill of legionella).
No Yes Maybe Bubba
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