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Small gas fired burner help

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  • Small gas fired burner help

    Hi Guys over here in HVAC, I am from the electricians section. I was called out for a service call at one of my clients recently because when they went to use their small gas fired heater that heats a small section of their house, it did not work. They thought it might be an electrical problem so they called me. I went out to look at things and found the problem was with the burner itself. The blower motor was rusted and was not turning so the burner would not fire because the safety switch would not allow it since it would not vent. Looking just from the outside there was alot of rust all over the exterior of the unit near the firebox. It's propane. It is vented with white PVC pipe. It appears to me that the way the unit was vented was wrong. I concluded just by my observation that there was condensation building up in the vent which was not getting exhausted to the outside and then dripping back down the vent pipe and into the fire box casuing it to rust out over time. Now I know there should not be this rust. I told the client that I thought the unit was not vented correctly and if they get a new unit, there should be some sort of correction to the venting. The way it was vented was pretty simple. Coming out of the top of the unit was a short stub of 1 1/2" PVC pipe, about 6" then it went to 3" pipe straight up to the ceiling and then eventually about 30 feet to the outside. It is my guess that the run of 3" pipe is too long for the exhaust vapor (which contains water) to be fully blown out the length of pipe before it condenses, as a result, water builds up in the exhaust pipe and drips back down into the fire box. It would seem to me that if the pipe was 1 1/2" all the way out, there would be enough pressure in the pipe to exhaust all the vapor. The pressue in the exhaust pipe obviously drops with the 3" pipe. Boyles law? Ok, well they got a new unit installed and they hooked up the vent same as before. No difference. No one could offer an explaination other than "the unit is old" for the rust problem. I saw the new installation and told my client I thought the same thing would happen over time, they said they told the gas people who installed the new unit about my theory and they said it was vented properly and that was the end of it. Ok, so my question to you experts is.... What is right with the venting of this unit?

    Thanks Lou

  • #2
    Re: Small gas fired burner help

    If the unit is designed for PVC venting the flue gases are going to condense no matter what size the pipe is. See if you can get a look at the installation manual. That will have the only approved venting methods in it. Usually the condensation from the flue gas gets drained. Its kinda weird that this one would just run back down to the burner with no drain line.



    • #3
      Re: Small gas fired burner help

      Well that is what I was told from another HVAC guy, he said there should be some sort of drain so the water gets drained off and does not go back into the fire box. The new unit was connected to the old vent system again. No drain.


      • #4
        Re: Small gas fired burner help

        Makes you wonder if the unit was installed without a permit. It certainly did not follow manufacturer's requirements, so by definition does not comply with codes.


        • #5
          Re: Small gas fired burner help

          lou, with hi efficiency units, the exhaust is going to be cool and condense.

          even with tankless water heaters, that are not running in pvc vents, have a condensate drain. the moisture is acidic. the venting actually slopes at first downhill to prevent condensation from re-entering the heater.

          it should be very simple look up the manufacturers installation specs.

          do you have a model #?

          phoebe it is