Question for Tim McElwain

Ironman

Can using CSST cause fog-horning in a mod/con? I've got a Lochinvar WHN 085 on LP that I've adjusted to the highest CO level allowed in the specs and it still does it at low modulation. I thought we had it cured last year, but the customer called back yesterday and said its started doing it again. The regulator is out side of the house with about 30' of 1" CSST and some black pipe and fittings near the boiler. There's also a range Teed of of it.
I've had several of this size WHN do this, but enriching the fuel mixture to the highest level cured all of them. This is the only one that has CSST between the regulator and the boiler that continues to resonate.

Tim McElwain

I have not heard of CSST causing fog-horning but have had reports of fog-horning with certain Mod/Cons. One of my contacts in the LP industry told me they eliminated it on several jobs by lowering the gas pressure coming out of the second stage regulator to exactly 10" W.C. pressure. They had found in several cases the pressure at 11 to 11.5" W.C caused different noises. Also at least 10 feet of minimum 3/4" black pipe before the equipment helped the problem.

4Johnpipe

Some manufacturers of tankless have recommended upsizing the CSST one size to reduce or eliminate system harmonics from the higher gas flow. It sounds like when you would spin a short piece of hose real fast...I've made this standard practice for fan induced sealed gas burners in general.

Ironman

Thanks Tim,
I'll try that.

The reason that I ask about CSST was that one manufacturer told us not to use a corrugated flex connector because that could cause it. I would assume the CSST would have the same effect?

I've also found that a long (18" or more) oversized nipple will work if it's not feasible to get 10' of black iron at the boiler.

Thanks for the up-sizing info John.

Ironman

Dialed the house regulator down to 10.0" on low fire; 9.8" high and the issue seems to have subsided.
Thanks, Tim!