Water Heater gas issue

Each time I would crank up the temperature for the water heater to come on I could smell gas. I placed my meter near the heater exhaust and it confirmed the presence of either carbon monoxide or natural gas. Within a minute it was fine. I also placed a smoke stick near the heater exhaust and it would blow away from the vent at the start up, but again within a minute would start venting properly.
I’m not sure what is causing this??

16 yr old natural gas water heater
No flame rollout on startup
furnace venting is attached below the water heater venting
furnace/water heater exhaust vent is above 2ft of roof surface, with no cause for backdraft

What am I missing?

That is acceptable.

Guess you should look that one up so you can test these things correctly.

I’ll take a stab at it.

It may be caused by the cold air at the top of the flue. Hot air rises and cold air sinks. When the exhaust first starts venting, it meets with the cold air coming down which would cause the initial backdraft. As soon as it warms up, it drafts properly. I would not be concerned.

There will always be a little smell when they start up. a small delay from when the gas is pushed into the burner to when the pilot ignites it. Sometimes the pilot need to be moved over or the flame increased if there is significant delay. As for the off gases rolling out, it takes a minute for the flue to get hot and a positive draft to start pulling it up the chimney. Very normal operation. You should take a couple of HVAC courses on NACHI to learn more about it as David said. The more you learn the better inspector you become. I have taken some of the courses a second time because there is no way to get it all the first time round.

Thanks guys but maybe I should have stated “I/we could smell an excessive amount of gas”, as in not a normal start up. The customer and I were approximately 4’ away. It first made me think the water heater vent was semi-clogged. Thus taking longer for the cool air to heat up to perform as normal.
I’ve not timed the start up process in the past, but this one seems to take 3 times longer plus the excessive smell. This is a SHORT straight run with one elbow.!?

The house is 16 years old and so is the water heater. The water heater is in the garage in what appears to be a newer utility closet along with the furnace. The water heater is sitting on two cinder blocks. This was the first clue that this may have been recently remolded. The dwelling has only been vacant for about a month. There are two other vents currently not being used…

Water heater is past its normal life I would budget for Immediate replacement .

I guess the best advice I can give without being there would be to write it up as you just wrote and call for the gas fitter/plumber.

Thanks Greg, I’m sure your familiar with something that just bugs ya and ya just can’t come up the the right answer or explanation. That’s what this is to me…I know what’s suppose to happen but???

So far I wrote it up for the block it sits on, which is not a perminate stable foundation for this appliance.

How did the burner look? Was there a bunch of debris on it? Delayed Ignition can be from a few different things. Bottom line is it is getting a bunch of gas in thier before it ignites. Should have been some roll out if the smell is that strong. As for the delayed draft I cannot figure that one out except what I said in my previous post. You may be on the right track. I did some training a year ago on a cracked heat exchanger and that was one of the issues. A delay of 15-20 seconds before the draft would start.

I was not able to get a good close look due to the water filtration system in front of the water heater*(see pic above)*. I did the best I could with my mirror, but you might as well say I didn’t see anything because of my poor eye site.:frowning:

Without being able to see the burner it can make it tough to diagnos. I think we need Charley on this one.