High pitched ringing/whistling from gas boiler

mx6er2587

Trying to diagnose a high pitch ringing or whistling type sound coming from my gas boiler (hot water radiators). The noise seems to be coming from around the bottom right of the unit and doesn't seem to be related to the water line side. Its loud enough to be heard on the first floor while the unit is located in the basement

Background: boiler is old, probably 70's vintage american standard but has run without fault for the past 5 years I've been in the home. I recently had the gas supply line replaced to facilitate the routing of ducts for a ducted mini split. The black iron pipe was replaced with identical sized black flexible CSST and the gas shut off valve for the boiler was also replaced with a new ball valve.

Is it possible my issue is related to this line change? maybe disturbed some debris in the old iron pipe?

Jamie Hall

Most likely related to the change from black pipe to CSST.

mx6er2587

checked the CSST with a mechanics stethoscope. Ringing like a bell. Will be calling the HVAC contractor back out to see what they say.

EBEBRATT-Ed

@mx6er2587

Good detective work. CSST is known to have that problem sometimes. They can either replace it with black pipe (more material and labor) or upsizing the CSST may work. It's the corrugations in the CSST that cause the issue. But black pipe it is a much better and safer job.

Although CSST is approved for gas you would be shocked if you cut a piece in half and looked at it. It's not much more than tinfoil with a plastic jacket.

JUGHNE

I have demonstrated the fragility of CSST by cutting a 6" length of it and letting the customer compare the weight (or lack of it) to a 6" iron nipple, both 1/2".

To many people weight implies strength and durability.

You would have to try really hard to get a nail or screw into iron pipe.

mx6er2587

Can anyone point me in the direction of some reading material on gas line sizing? I see the CSST manufacturer has tables on their website but I'm not sure which table I should be using.

https://www.gastite.com/downloads/pdfs/gastite_sizing_tables_natural_gas.pdf

Hvacdingus

Was your boiler recently installed? The whistling could be the venturi tube inside the boiler fell off causing it to whistle.  Or your boiler is starving for combustion air and it's pulling it in anywhere it can. So if you have a high eff. Boiler check your combustion air intake outside and if there is anything clogging it in the boiler access.

mx6er2587

no boiler is a 50+ years old cast iron beast. The only recent change is from black iron pipe to smaller diameter CSST on the line that feeds the boiler.

This change was made because the routing of the old line interfered with placement of the main trunk for a newly installed ducted mini split system. (old line hung down below joists and would have required the duct work to sit almost 6" lower. New line runs between joists allowing the duct work to be tucked up nice and tight)

mx6er2587

Just to close out this discussion. The HVAC contractor after much poking and prodding agreed to swap the 1/2" CSST for 3/4" black iron. Whistling noise has been completely eliminated.

pedmec

i would bet your csst is the problem. csst does not provide the same volume of gas. 1/2" black has less of pressure drop compared to the equivalent 1/2" csst. pipe reduction causes increase in velocity. the increased velocity combined with the spiral design is creating the noise. is this natural gas?

mx6er2587

Yes this is exactly what was happening. Problem has been fixed already .

EBEBRATT-Ed

CSST is junk in my opinion. Gas is to hazardous to be contained in a piece of tin foil with a plastic coating.