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Single stage furnace - gas velocity?

Mikar
Mikar Member Posts: 16
edited February 13 in THE MAIN WALL
i have a single stage furnace. I notice at times the gas piping to the unit is louder than at other times. When I refer to sound, I mean the hiss you would hear with your head in the vicinity of the pipe?

Like for example with the burners on, it starts off quieter upon firing up and then in the middle of the cycle it sounds like the velocity has picked up because the hiss becomes louder. Other times, it a consistent sound throughout the entire furnace cycle and no change is detected.

I also noticed if I put my ear directly on the pipe, I can hear the flow pulsate.

If the furnace is a single stage, what account for the difference in velocity that I am hearing? And from what I am describing, does it sound like I have an issue?

Comments

  • ratio
    ratio Member Posts: 2,794
    Other appliances using gas at the same time?

    BTW, would this by any chance be CSST (flexible lines) or an appliance flex connector? The only time I've heard velocity noise in a gas line was in severely undersized appliances connectors or undersized CSST. It's supposed to be sized for ½" WC pressure drop at max flow, which is literally the pressure it takes to suck water ½ inches up a straw.

  • Mikar
    Mikar Member Posts: 16
    edited February 13
    I should have mentioned, it is not csst and there is no other gas being used. And I dont notice it when I am using the water heater or stove which consume less gas of course.
  • Mikar
    Mikar Member Posts: 16
    edited February 13
    Looking further into this i notice the gas sounds like someone is closing and opening a valve at times.... its a fluctuating sound. I have never noticed it before today.

    Im concerned, its about 0 degrees outside right now and falling and dont know if i should call for emergenct service. The furnace is running and heating correctly.
  • pecmsg
    pecmsg Member Posts: 2,071
    Without measuring the gas pressure we can only guess
  • Mikar
    Mikar Member Posts: 16
    edited February 13
    I had gas utility over and they showed me a steady 6 wc at the meter..... guy said if the heat is working to not worry qbout it. Of course he didnt check the furnace.

    Should i open up a can of worms with an emergency call to check gas valve?

    Have you ever seen faulty gas valves do this?
  • pecmsg
    pecmsg Member Posts: 2,071
    You need to check at the appliances. 
  • Mikar
    Mikar Member Posts: 16
    edited February 13
    Yeah i understand i called the gas co first thinking the regulatoe..... but i am not sure i should open up this can of worms after hours on below zero night when the firnace is working.

    If gas pressure wasnt correct at unit, fluctuating as i describe, wouldnt it be tripping on safety?
    Does gas velocity to a single stage valve change during operation?

  • pecmsg
    pecmsg Member Posts: 2,071
    Mikar said:
    Yeah i understand i called the gas co first thinking the regulatoe..... but i am not sure i should open up this can of worms after hours on below zero night when the firnace is working. If gas pressure wasnt correct at unit, fluctuating as i describe, wouldnt it be tripping on safety? Does gas velocity to a single stage valve change during operation?
    Test the gas pressure and stop guessing!
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,190
    I would check the gas pressure at the furnace gas valve inlet while the burner is firing. Did the gas company do this or was the furnace off?

    Sounds like their regulator is hunting
  • Mikar
    Mikar Member Posts: 16
    edited February 14
    They just checked at the meter right after their regulator with the burners firing.

    Whatever it is it is intermittent, it hasnt done it since they gas co left, been about 3 hours but im still freaked out.

    The furnace is on, we have heat and its after hours on a sat. on the most frigid night this year. Do you think this warrants an emergency call?
  • HVACNUT
    HVACNUT Member Posts: 3,946
    I think your over reacting. There's nothing to worry about until there's something to worry about. If the furnace is from the twenty first century it has plenty of safety controls to shut the system down or prevent it from firing in the first place if there is an issue. 
    Other than the noise, everything is peachy but place a call on Monday and let them know you'd like it checked. Specifically lockup and manifold gas pressures and pressure drop across the gas valve, as well as a combustion test. 
  • Mikar
    Mikar Member Posts: 16
    edited February 14
    Thanks hvacnut, thats the approach i have to take at this point.

    I dont have a manometer. However, i clocked the meter as per the installation manual, counted 2 revolutions of the 1 foot dial and divided by two and it was correct. That is assuming i am still getting 3.5 wc as i did the last time a tech measured about 5 years ago and the 6wc the gas co showed me after their reg today.

    What does this tell me? If i had an issue, would i have seen a major difference when counting revolution?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,190
    It could be the outside regulator fluctuating a bit but there is also a regulator built into the burner gas valve to smooth things out.

    I would call them Monday but if they checked the pressure with the furnace running it sounds ok. Have them come out and listen to the noise your hearing. I wouldn't stress over it
  • Mikar
    Mikar Member Posts: 16
    edited February 14
    Does clocking the meter as i describe determine if manifold pressure is correct if i am getting the correct btu according to the chart in the manual?

    The "hunting" "surge" sound i hear you have to put your head/ear almost directly on the pipes to detect... a service guy is going to think im nuts. It does it from the time the burners first fire and for the first minute or so before it evens out. In fact its not detectable at all standing next to the furnace... i noticed in an adjacent room away from the normal mechanical noise of the unit in operation.

    Could abnormally cold weather cause gas flow sound to fluctuate?
  • Mikar
    Mikar Member Posts: 16
    I fired up just the water heater today and I noticed the same hunting/surging but to a much lesser extent with just that appliance working. The furnace was not on at the time.

    That points back to the supply then correct? If nothing else has changed in the house, should I be pointing the finger at the meter?
  • motoguy128
    motoguy128 Member Posts: 351
    With the really cold weather, the main gas header at the street could be near capacity. Maybe fluctuating some as appliances in your neighborhood cycle and and off. So the regulator maybe use be modulating more than usual.
  • Mikar
    Mikar Member Posts: 16
    edited February 14
    Thats what I am leaning towards at this point... hopefully hearing this with the water heater lets me rule out the furnace as malfunctioning.... but I will get pressure checked at the gas valve for piece of mind anyway.
    So maybe there isnt a problem afterall. Should I press with the gas co?. Im not sure how to proceed since their guy seemed confident everything was ok since he was showing stable reading at the meter after the reg.


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