Gas water heater smell...

[seamlyne]

So, last night I'm trading out laundry loads, standing between the washer/dryer and the water heater. We've been running hot water for the dishwasher upstairs, and the last laundry load was a warm load, so the burner on the water heater kicks on. I heard the "whoosh" of the burner lighting up, but I noticed a smell a second or two later - natural gas maybe? (No, it wasn't me.) It dissipated in a moment or two, and I never smelled it again, and I've never smelled it at any other time. It reminded me a lot of the basement at my grandfather's house, where every appliance with a burner was gas-powered.

It's like the gas outlet opened and a little of the gas escaped before the pilot got to it. Should I be concerned? Or, more accurately, what should I be concerned about?

- Wm

Measure with a micrometer
Mark with a crayon
Cut with an axe.

[LazyPup]

If it was just a little wisp of odor and dissipated rather quickly there should be nothing to worry about.

When the burner first lights the combustion chamber, water heater flue, and the exhaust flue are relatively cool. It takes a few moments for the heat to rise up the water heater flue and into the exhaust flue to start the exhaust process. During that time a small amount of the combustion exhaust may exit out through the draft hood air intake, which would give a faint wisp of gas odor, but the flue should heat up rather quickly and begin to draw air into the draft hood and up the chimney.

There is one possibility that should be checked. Look under the gas control and you will see a service access cover into the combustion chamber. On the new water heaters the service access is sealed, but on older models there is supposed to be a galvanized metal cover that fits rather loosely inside the access. If that cover is missing, under rare circumstances a draft of air near the floor can push the raw gas back away from the pilot flame as the burner comes on. In that situation the combustion chamber fills with a bit more gas before the gas reaches the Pilot flame and causes ignition. The end result is when the gas ignites it tends to flash back and would cause some of the gas or combustion by products to vent out through the service access. Normally if the draft cover is missing or mis-positioned there will be faint traces of black soot on the outside of the water heater immediately above the access opening.

[seamlyne]

quote:Originally posted by LazyPup

If it was just a little wisp of odor and dissipated rather quickly there should be nothing to worry about.

So it is. My wife mentioned to me last night that she notices it when the furnace kicks on - and it's not that "first on for the season, burning off the dust smell".

quote:Originally posted by LazyPup

There is one possibility that should be checked. Look under the gas control and you will see a service access cover into the combustion chamber. On the new water heaters the service access is sealed, but on older models there is supposed to be a galvanized metal cover that fits rather loosely inside the access. If that cover is missing, under rare circumstances a draft of air near the floor can push the raw gas back away from the pilot flame as the burner comes on. In that situation the combustion chamber fills with a bit more gas before the gas reaches the Pilot flame and causes ignition. The end result is when the gas ignites it tends to flash back and would cause some of the gas or combustion by products to vent out through the service access. Normally if the draft cover is missing or mis-positioned there will be faint traces of black soot on the outside of the water heater immediately above the access opening.

I know just the thing you're talking about, and it's in place.

The thing that gets me is that I've lived in the house since I was four, now own it with my wife and two bairns, and I've never noticed the smell before. Back in the summer we had some plumbers out to plumb a new laundry area and re-route the gas pipe to the dryer's new location (you may remember a post about trying to find out where a pipe in the floor goes - an abandoned septic system, as it happens). Assuming all connections are good, and I've no reason think they're not, would some change in the system somewhere cause this to start happening?

Just had a thought, too. Both the furnace and the water heater vent into the chimney (nothing else does...its only function is for venting). Wonder if something there could be causing a draft back? The O2 detector's never gone off, but...

- Wm

Measure with a micrometer
Mark with a crayon
Cut with an axe.

[LazyPup]

IF it is just a faint wisp of the odor when the burner first comes on, then dissipates quickly I doubt if there is anything to worry about.

You stated in your original post that you first noticed it while working in the laundry, which is adjacent to the water heater. You probably never noticed it before, buy now that you have you are more conscious of it.

That slight odor will be more pronuounced in winter because the air in the chimney flue is colder and requires a few more moments to preheat to start the draft. Also, it is probably a bit more noticable on days with high barometric pressure as combustion gases are heavier than air which would cause a bit of delay in establishing the draft.

Just to be sure, you may want to examine the flue pipe from the heater to the chimney. Make sure there are no rusted spots, all joints are firmly screwed together, and their is a good 1/4 inch per foot pitch upward from the burner to the chimney. Also make sure the pipe is sealed into the masonary of the chimney wall.

Also measure the length of the run from the top of the heater to the chimney. The horizontal run should not exceed 75% of the chimney height. (If the chimney is 20 feet high the horizontal run should not exceed 15 ft)

Visually inspect the gas flame when the burner is on. The flame should appear a darker blue color near the heater and lighter blue at the top of the flame with just the occasional wisp of yellow tips on the flame.

If you see a substantial amount of yellow on the flame tips you may want to have a service man adust your burner.

If you just get a wisp of the odor when the burner lights, the flue checks out ok, and the burner flame is okay you should not have anything to worry about.