Melted Plastic Top Of Water Heater

Big-Al_2

I installed a new 50 gallon Richmond (Rheem) natural gas water heater in my house last October.  It's vented into a 6" metal lined chimney with a built-in critter cap, shared with my boiler.  All seemed OK. The draft hood was properly installed and the flue pipe has the correct pitch, etc.  Last week, for the first time, I noticed that some plastic parts on the top of the tank, the ones that surround the water pipe inlet and outlet, were somewhat melted, obviously from hot gasses coming out around the draft hood.  I'm wondering if there was some kind of downdraft condition that caused flue gas to escape around the hood for a while.  (We did have a couple of bad storms with really high winds lately.) A carbon monoxide detector installed in the general area reads zero, and the unit seems to be venting just fine now.



So, what is happening here?  Should I be concerned?

Mark Eatherton

Absolutely!!

ANY time you see evidence of flue gas spillage, you should be EXTREMELY concerned.



By law, atmospheric appliances are allowed to spill initially, until daft is established, but this is allowed for only a few minutes.



There are many conditions that can create a back draft condition that would cause draft hood spillage, including mechanically induced, wind induced, building induced and more.



You should get it checked and corrected so you don't end up as a statistic in the Carbon Monoxide section of this web site...



Go to National Comfort Institutes website and see if there is a qualified expert in your area.



ME

Big-Al_2

Thanks!

Thanks, Mark!   I looked on the National Comfort Institutes site, and the closest contractor is fifty miles away.  For now, I'll do some investigating myself.

 I do have a peak-recording CO monitor plugged in less than ten feet away from the unit, and it consistently reads zero.  I fired up the boiler last night, and ran it for about twenty minutes.  The water heater flue connected to the same chimney remained cool to the touch the whole time, so apparently there was a good draft in the chimney.  Maybe the problem is in the water heater flue itself. I will try a smoke test tonight near the water heater draft hood and see what I get.  A HVAC tech I do a lot of business with is also going to lend me his flue gas analyzer tonight so I can check the combustion mix of both appliances and look for evidence of spillage myself.  (We are having a major wind storm here this afternoon, so maybe it will have to wait until tomorrow.) 

If I get the chance, I'll post a few photos too for y'all to see.  Maybe the routing of the flue vent pipe is wrong.  I've never seen it done that way before, even though it was originally installed by a licensed pro.

Charlie from wmass

do you know the total

BTU load going into the chimney and the height? This is what determines size of a liner not whatever size they can fit into the flue as I have seen done.

Big-Al_2

Maybe Too Small

The effective height of the liner is right around 30 feet.  The boiler is 175,000 BTU and the  water heater is at 35,000 . . . for a total of 210,000 BTU.  The liner is six inches round . . . which from looking at the charts may be marginally big enough or just a little too small.  The guy who put it in is a reputable dealer, so I never thought to double check his sizing.  There is plenty of space in the chimney for a bigger unit.



The strange thing is that the problem seemed to occur over the summer, when the boiler was turned off.



I didn't get the flue gas analyzer today, but a flame held a couple of inches away from the draft hood definitely got sucked toward the flue.

Bob Bona_4

liner

is just shy. 7" would have been right. Enough combustion air?

If you have a whole house fan, be sure windows are open before using.

You should see some of the carnage from oil burner innards when those helicopters run. I had one job where they burnt something while cooking and decided to expel the smoke via the fan. Windows shut. It was ugly.

Tim McElwain

This is the test you want to run:

Close the house up tight including the fireplace if you have one. Bring on all the fans in the house, attic fan, vent hood for cooking stove, bathroom exhaust etc. Now bring on all the equipment boiler, water heater, dryer and then check your draft at the vent connector it should be a steady -.01 to -.02. If it is spilling back into the room then you have a reverse chimney caused by a negative pressure in the building hence the greater pressure from outside will spill back down the chimney.



I also suggest you put a spill switch (blocked vent switch) and tie it into the thermocouple on the water heater, that way when it spills it will shut off and prevent products of combustion from getting into the building.



Is this water heater one of the new FVIR water heaters? If so what size flue is on the water heater? Is the flue single wall or double wall? These type water heaters are now the required system so if it is a new heater it is FVIR. They tend to run with very high temperatures at the top of the water heater so you may want to test the flue gas temperature.

Jamie Hall

If I might add...

to Bob Bona's comment -- 6" is not really "just shy" of 7" -- the flow capacity and resistance is proportional to the square, so you actually have only 3/4 of the area in that flue which you really should have...

Tim McElwain

A 6 " Flue

is 28.27 square inches allowing 6500 BTU's per square inch that flue will only handle about 183,000 BTU's.



I would love to see a picture of the flue connections so I can judge what might be the problem.



What are the actual size of the flue connection on the boiler and water heater?

Jack

And in the mean time...

like right now, combustible gas detector and carbon monoxide detector. Sorry to scare you, but I think it is reasonable, and I do have them in my home.

Bob Bona_4

what chart are you going by?

I make a 6" liner with combined appliances at 30' good for 205,600. Almost there with the inputs of 210,000 total.

7" should get you 279,200.

Unless I'm looking at the wrong charts.

Tim McElwain

Bob, I am using the AGA

and Batelle Labs criteria which I find more accurate than the code book charts as to actual capacity. AGA used to use a range of 4,500 to 6,500 BTU's per square inch for determining flue sizing on conversion burners. In recent years as I looked at the revised charts I found that on the high end of say a 6" flue around 200,000 to 210,000 I would have problems from time to time. Keep in mind there are a lot of 6" flues out there. Using the 6,500 BTU's per square inch got down to around 180,000 so I use that and go to 7" to be safe.



Another issue here is temperature and with a lot of higher efficiency equipment we have lower stack temps so then the 7" may be difficult to get proper Delta T. In that case I will go with the 6" and find it is more than adequate. I also teach to go no lower than 4" on any connection and to use double wall for all connections and also the common vent. My advice to all my students is this, the code may tell you it should work but the truth is it has to work and when it does not then we need to get a little more severe in our calculations. In the case we are talking about here with 30 feet of height that should more than compensate for any slight drop in Delta T. Draft being created by Delta T and height we have nothing else to go on unless we power the vent system.



FVIR water heaters have had a problem with excessively high temps at the top of the flue passage (500 to 600 degrees net) especially when the cordite air entrainment get plugged with dust and animal hair and fur. 

Mark Eatherton

Corrugation effect

Tim, et al. Doesn't a corrugated liner, the flexible type also have a higher inherent pressure drop due to friction against the corrugation, thereby requiring a larger diameter to compensate for the roughness?



I have no charts any more, other than Ohms Law :-)



ME

Mark Eatherton

E V E R Y building should have one or both of those...

It should be a nationwide law. It is a law in Colorado, but doesn't require existing buildings to be retrofitted. Better than NO law...



I guess not enough senators family members have been overcome by CO, or it would be a law, like the FVIR requirements for water heaters...



ME

Tim McElwain

That is correct mark a corrugated liner

has about 20% less capacity than a straight "B" vent (double wall). In fact about a year ago I had a six house complex owned by the state that had installed liners in all the chimneys and the reduction was so great the new boilers and water heaters would not draft properly all the time. To quote the state guy hey a 6" flue pipe is a six inch flue pipe, obviously not always so. Those have since been upgraded to Mod/Con units with indirects and side wall vented. The taxpayers paid for that mess.



Each manufacturer of liners have charts that show capacity and if you do the math compared to straight "B" vent they are anywhere from 15 to 20% less capacity. I tell installers if you can just install a straight "B" vent into the chimney and be done with it.

Bob Bona_4

thank you

Tim, good post.

Tim McElwain

Big Al we have not forgotten about

you. Have we helped you to perhaps come up with a solution to your problem?

Big-Al_2

Thanks Again

Sorry for ignoring the topic . . . long day . . . just got in at 10 PM.  I WILL be getting a combo combustible Gas/CO monitor for the basement and will move the existing CO monitor up into the living space.  The batteries in my digital camera are dead right now.  Maybe I can post a couple of photos tomorrow.



Tim, I will run a test on the stack by closing up the house, turning on anything that vents outside, and firing up the boiler and water heater.  I will try to come up with the right differential pressure gauge and check for a negative pressure in the stack.  We used to have one in our instrument cabinet at work, but I may have to do a little digging.  If I can't come up with that, I will at least do a smoke test to make sure that there is a good draw into any draft hoods under worst-case conditions. 



It is a FVIR water heater, so what you said about high combustion gas temperatures might be the case.  I don't know about using a thermal blocked vent switch on the water heater, because if the stack is downdrafting badly enough, the switch might stay cold anyway.  It's odd in the first place the way that Rheem built the water heater.  It has plastic flanges around the water connections that are actually sticking partway under the draft hood.  It's almost like they wanted them to melt with the first whiff of spillage.



If I am overwhelming the chimney liner, then maybe I can figure out how to downfire the Burnham IN6 boiler somewhat.  It is way oversized anyway.  I have an inquiry into Burnham about that already.  Like I said earlier, I do have access to a decent flue gas analyzer, so I could set it up properly, and my HVAC tech friend would give me some guidance.  Or, I could install an induced draft water heater and vent it through the wall.  Either one would be cheaper than replacing a chimney liner that's just a little over a year old.



In the meantime, I do have a working CO monitor, and the boiler is turned off, so I'll probably not die from spillage before I get it figured out.  I might not get around to investigating for a few days.  My lovely bride and I will be traveling southward to visit with her very ill elderly father in the next few days.  He's had a good run of it until a few weeks ago, but now he's fading fast.  We're going to miss him when he goes, so we want to spend some time with him while he's still on the sunny side of the sod.

Tim McElwain

Al keep us posted

Also our prayers are with your father in law, have a safe trip.

Robert O'Connor_12

L=Lateral ft.

According to the sizing table(s) listed in the IFGC Section 504.2(1) & 504.2.(2) the L or Lateral feet comes into play when determining vent size. Without knowing this number accurate sizing is but a guess. As an example, if you use chart 504.2(1) and go to the 6" diameter line and then read over to the L @ 15'ft, it says you can vent 249k, however you get a 20% penalty for using a liner system. The maximum for this would then be only 199.2k.

I think something else is happening here. Could be that the boiler being off for the summer and just the water heater venting through combined with possible lack of adequate combustion air and something else like a mechanical fan on say a exhaust hood from your kitchen, clothes dryer, bath fan, down-draft from high winds or combination of all four. Keep in mind appliances use appox. 50 cubic feet of combustion air for every thousand btu's, and that most older homes especially if the basment has been renovated and most of the availible combustion air has now been choaked off by the installation of energy efficient windows and vapor barriers in the wall cavities these other mechanical devices will win in a competion for the availible air.

Sorry to hear about the father-in-law

hope this helps.



Robert O'Connor/NJ

Big-Al_2

Photo Attached

Thanks for the guidance and support.  Here is a photo of the top of the water heater.  Notice that the elbow at the top has a bit of an offset to it.  I'm thinking I should rotate the wye on the 6" lateral  down a little.  That would give the water heater lateral a little more pitch and line things up better.



The boiler is way oversized for the connected radiation.  Burnham says I can downfire it 10% by reducing the manifold pressure, as long as I stay above a minimum pressure.  That would get me down under 200k BTU total.  It might save some gas too. I'll get my HVAC buddy over and we'll give it a try.

Tim McElwain

The connection into the

6 inch should be with a tee or a dedicated wye fitting.



I do not agree with derating your boiler by reducung gas pressure. What did they tell you was the minimum pressure? Who did you talk to at Burnham?

Big-Al_2

Customer Service

Via email:

Thank you for contacting U.S. Boiler Co. We do not recommend reducing the capacity more then 10%. Your contractor can reduce the capacity by either reducing the manifold pressure (not below 3 inches of Water Column) and/or reducing the size of the orifice.

Regards,

Customer Service

US Boiler

Tim McElwain

If you have to

reduce the orifice size and leave the pressure alone. Have a professional do this who also knows how to do a combustion test to insure maximum/safe efficiency once the boiler is down sized. I am not a big fan of downsizing but I can't argue with the boiler manufacturer if they want you to do it.

Big-Al_2

Will do

Thanks again!

My local HVAC buddy says he will get me the right sized orifices for the boiler, so I can do the job right, and after I have things swapped out and fired up, he'll come over and help me set up the burner properly.  While he's over, we'll also do a flue gas test on the water heater to make sure it's not producing too much CO.

The boiler may theoretically have the best thermal efficiency at full fire, but this one is short cycling the way it is, so maybe it will actually save some energy to dial down the burners.  I'll know for sure by January . . .