EDIT: SOLVED. IT WAS THE FLEX CONNECTOR. THANKS EVERYONE. My gas furnace makes a high-pitched whining sound when the burners turn on (when I can see fire). A repair man came and told me it may be that the “flex connector hose” that goes from the gas line to the furnace. He said the flex connector is 1/4 inch when the gas line is 1/2, creating a bottle neck, stifling the system from getting enough gas. Could that possibly lead to a high pitch noise that is always present when burners are on and on occasions can be heard anywhere in my small home?

  • Are the flames a clean blue colour? When was it last serviced? – Andrew Morton Jan 11 at 18:08
  • What make and model is the furnace? – ThreePhaseEel Jan 11 at 18:37
  • Without a more specific description of the sound (a "high-pitched whining sound" could be just about anything), there's no way to know what the answer to this question is. Important pieces of information not in your post include whether this is a new sound, how you discovered it, whether you've ruled anything out already (such as the combustion vent fan), etc. – Peter Duniho Jan 11 at 19:47
  • The sound was there when I moved into the house 8 months ago. I had it inspected but not serviced. – Luigi123 Jan 12 at 15:08
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    On all Stack Exchange sites, it is against community guidelines to add "solved" or similar to the title of a post, as well as to provide the answer in the question. If none of the existing answers addressed your problem but you were able to solve it some other way, post an answer to your own question, and click the "accept" checkmark on your post. Looking at your update and the existing answers, it seems like you should have left your question post alone, and just accepted this answer from @EdBeal. – Peter Duniho Jan 14 at 23:40

It's unlikely that going from a larger pipe to a smaller pipe (which is essentially what the flex hose is) would cause that. However, the repair man may have meant that the flex hose was undersized for the gas line inside the furnace, which would make more sense. Expanding flow could certainly cause the noise, but to really figure out what's causing it you'll need a mechanic's stethoscope. They're pretty cheap, but you may even be able to get one as a loaner tool from an auto parts store.

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  • Your first 2 sentences (based on my poor understanding) sound like the same exact thing [hose leading to furnace is smaller than it should be (1/4 inch diameter) for the strength of the furnace] and therefor they seem to contradict each other. What he meant was that the corrugated steel looking hose that connects to the furnace is not wide enough and therefore the furnace is not getting enough gas. The main gas line is 1/2 inch, so he says the connector flex hose should be 1/2 inch too. Is that a possible reason? – Luigi123 Jan 11 at 17:51
  • @user111046 the problem you described the repair man telling you was that the main gas line was larger than the flex hose. The problem I was describing was the flex hose being smaller than the furnace's interior gas line. Either way, the solution would be to replace the flex hose, but you need to figure out exactly where the noise is coming from unless you're going to replace parts at random and see if each one fixes it; it may not be coming from the flex hose at all. – zaen Jan 11 at 19:41
  • We call it the "Canadian Tire" method of repair. Keep changing parts until the problem is gone. Then tell the customer all those other parts were needed also. Unfortunately, I have seen this happen at Canadian Tire Auto Service. By the way, a stethoscope works only with a vibration noise source. Try using a 2-foot length of garden hose to find the squeal noise. – John Canon Jan 12 at 3:03
  • @zaen Thank you for your clarification. The guy was sent by my home warranty company. Should he have done more to diagnose the problem? I read online reasons for "high-pitched sounds" can be: shaft bearings need some more oil, bearings need replacement, blower belt is loose, slipping, or fraying. He ruled out the blower belt because he says mine should not have one... (not sure if that's true) What should I do next?? I still haven't sent him his payment (co-payment). Thank you so much. – Luigi123 Jan 12 at 14:34
  • @zaen Also important. When I close the gas supply about 30% it changes the pitch of the sound (it lowers it). But the sound doesn't go away. – Luigi123 Jan 12 at 15:10

I had the whistle in my last home ,, actually in my shop , the corrugated flex whistled when it was at full blast. Last try for tonight connect or ? Problems. I upsized from 3/4 to 1” flex and the whistle was gone, it’s the flow and the ripples that make the whistle, upsize the flex 1 size you double the area and noise gone, ok last time . ok this worked for me it made a huge difference , after doing this my hunting buddy said look at your elk call exactly the same blow two hard and the squeal scares them off, my shop heater was 125 or 25

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If you’re hearing the noise when the fan kicks on, it could be that too restrictive a filter is installed.

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