Need advice: high pitch noise from gas line

logocde

I am overwhelmed! Didn't expect to get so many responses in such short time! Thanks for chiming in, guys! Also Just realized that I can upload photos. So I attached some here. Hope this helps as I am not sure what some of the terms means.

I believe it's Goodman. My old Rheem stilled worked well at the time of replacing. But AC gave out and considering the furnace is 20 years old, so I agreed to replace both.







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Ever since the contractors put up the new furnace (100 k BTU) in the attic above my master bedroom, I've been hearing high pitch noise when it's on. Oddly, the noise is not directly from the furnace, but can be heard the loudest in the kitchen, which is right below the master bedroom. It can also be heard in the garage, where I have 1" gas supply line coming into the house. The contractor came back once to address the issue by "turning the furnace gas valve to minimum", at least that's what I was told. The noise was much smaller to almost gone. But a couple hours after he left, I turned the furnace on, the noise came back again.

I googled myself and found an article talking about similar noise caused by undersized gas lines. So I went up to do a quick check: I saw 3/4" line coming into the attic and then converted to 1/2", which is then connected by a 1/2" flexible line to the furnace. The furnace location is 80-100 ft away from the gas meter. The noise comes up as soon as the burner kicks in, regardless if I am using other gas powered appliance or not.

Outside the house, I only hear the flow sound from the meter, no such noise. Does this sound like an undersized gas line to you? Or do I have a faulty valve in the furnace?

unclejohn

Sounds like your service tech. may have set your furnace in low fire only. Don't know about " turning gas valve to minimum ". I would also ask to get rid of the flex pipe. Is it high or low pressure gas meter? What make and mod. of furnace. Did you have a furnace there before or is this a new install?

HVACNUT

Was a combustion test done? Natural gas or propane? You will get quite a whistle if its propane but the valve hasn't been converted. 
The combustion report will tell us more.

ratio

Is the gas piping hard pipe up to the flex connector to the furnace? I've had those flex connectors whistle when they're sized on the small side. As the plummer refused to change them, I managed to lessen the noise by adjusting the flex line (it was long enough that I could twist it up somewhat). There should be a tag on it, with a table that gives size, length, & allowable BTUh. Make sure you're not exceeding that—if so, have the contractor replace it with one that's properly sized.

Intplm.

@logocde

You should also check that all the pipes and ductwork are secured properly. Its surprising sometimes what type of noise can be heard from a vibration.
The next time you hear the noise, go to the heating unit and grab hold of the pipes and or the ducts firmly and listen for any noise that might change and go from there.

JUGHNE

If there is no tag on the flex then it may be a section of CSST.
What color is it?

100,000 is a lot of furnace to stick in an attic.
Depends upon the location and size of house.
Is that the only one in the house?

Ironman

The flex line is under-sized. Replace it with a larger one or iron pipe and the noise will be gone.

EBEBRATT-Ed

If the furnace is 80-100 feet away from the meter and he came into the attic with 3/4" you gas line and the flex connection are likely undersized.

Flex connections are also known for causing noise.

Was the gas piping tested and inspected?

And they need to do a combustion test

logocde

logocde

I'll also try some of the tricks mentioned here and update tomorrow.

Lard

logocde said:

In addition to the flex being undersized, the drip leg is completely wrong, indicating that the entire gas line install should be checked by a qualified tech.
Disappointing when a few nipples and a union would make a direct black pipe connection.

SuperTech

It really doesn't look like it would have been difficult to pipe in that gas line without using the flex connector.  I would definitely get rid of it.  I've seen them cause noise as well. 

unclejohn

The gas pipe thats holding up the flex needs a support so when someone steps over the flex and misses his footing the gas line will not break off.

EBEBRATT-Ed

And the low voltage wire laying on the plywood tells you all you need to know about the installer