transformer gasket not enough to prevent indoor odors in direct vent

Pete_in_Jersey

Brand spanking new ThermoDynamics TDX90+ condensing boiler (it hasn't condensed anything yet) with Carlin EZPro burner and direct vent.  Positive draft through the entire system (except for the 4" combustion air inlet ductwork that is), so it should leak anyplace there's any gap or hole.  Slight oil smell in the basement; slightly oil-smelling air is coming out near the transformer hinges, where there's no gasket.  I don't know what the gasket's supposed to do anyway; there's a U-shaped cutout for the Cad cell that seems to allow any pressure to bypass under the gasket anyway, back towards the transformer hinges.  I couldn't find any air coming out any of the flue piping joints, and there's zero smoke and no CO.  I'll check excess air via O2 analyzer shortly.



Should I just goop the transformer lid down with silicone all the way around?  Seems like that's an amateurish solution. 

Steamhead

Positive pressure

how much positive pressure do you have, and what's it supposed to be? 

Pete_in_Jersey

pressures not excessive

The positive pressures are not excessive; 0.08" water column over fire (0.12" spec) and 0.03" just past the boiler in the direct vent gas testing fitting (0.02" spec).  This being a direct vent system, the pressures are not adjustable independently of air/fuel ratio.  That is, there's no barometric damper (or damper of any sort) in the flue.

Charlie from wmass

can you remove a

90 or turn a couple into 45's to reduce the run? How far are you pushing and how many elbows are you using?

Pete_in_Jersey

no elbows at all

The flue ductwork in the direct vent kit is one unbroken 7 foot length of 5" ID corrugated stainless.

Charlie from wmass

were you careful

with your radius bends?

add

i would recalibrate

the burner, maybe with smaller nozzle,sometimes the manufacture spec are made for ideal situations.also i would like to know if the smoke pipe on the outside wall is it right under a ledge and is it been windy in your area.

Pete_in_Jersey

the 1 flue bend is very gentle, and the nozzle is the smallest...

...recommended by the boiler factory for this boiler.  Going up in nozzle size (not needed here; there's actually room to go smaller but I hate to violate the manufacturer's spec) of course would generate even more positive pressure and make any such problems worse, so I'm concluding that Carlin hasn't figured this out (yet).  I would think it obvious that a positive pressure system needs to be completely sealed, and this one's not.  One might think that theoretically, the outleaking air at the transformer hinge location should only be fresh combustion air, but the oil nozzle is what, inches away, and there's all kind of air turbulence going on at the discharge of the wheel, so I'm not surprised that there's some oil vapor backmixed in the transformer area.  In fact, the somewhat smelly outleaking air (it's not so horrible that the basement is unusable) is already noticeable when I put my nose down there during the 15 second pre-purge, when no oil is spraying.  I doubt that the 120 second post-purge can completely strip the combustion chamber of any traces of oil.  The Carlin tech service guy at the factory said they haven't heard any complaints so far, but did suggest using a stick-on foam gasket to cover the areas their gasket fails to cover.  I'm thinking the silicone could be done neatly enough that it wouldn't actually be so bad, now that I think about it.  Can't hurt to try; I may be making more out of this than necessary.



The flue outlet is not under a ledge, and it's not  windy (house in the middle of the woods).



I haven't heard about the Dornback problems; I'll have to search on the topic.



Thanks, guys; I'll report back.

World Plumber

Combustion air

Are you getting enough combustion air? Are you pulling air from outside or the utility room?  If from the room try opening a window.



Double check those pressures the sound high to me. The transformer gasket is to prevent it from sucking air in and affecting the combustion.

Pete_in_Jersey

silicone sealant - simple solution

Doesn't even look all that nasty; most of it's hidden inside.  Red silicone sealant to make a new gasket covering the area that's not sealed by the factory gasket.  Opening the hinge after the silicone is destroys the seal right at the hinge though.  Gotta re-do that part.



Wonder why Carlin hasn't fixed this yet.  These positive pressure burners aren't that new are they?  I'm thinking that with a negative drafted system this oil odor would never happen, since air is getting sucked in at any gasket leaks.

billtwocase

Is this

a combo intake/exhaust system? If so, it may be cross contamination? I would also recommend an Honeywell/Beckett control with an adjustable post purge. I'd like to see at least a 3 min, preferably 4-5 min post purge for direct or power vent systems. That after burn doesn't disappear that quickly, and a hot blast tube assembly will give off those odors if not cooled down enough

Pete_in_Jersey

pre and post purge timing also play into this?

yes, this is a combo intake/exhaust system, at least at the outside wall, where the intake air is drawn in around about a foot or so of exhaust flue, extracting yet more heat from it.  It's two separate ducts all the rest of the way.  I could see how a faulty weld in the through-the-wall direct vent fitting would allow exhaust to be sucked into the intake line.



But my problem has been an oil smell coming out of the pressurized transformer area, not an exhaust smell.  The silicone cured it. 



But your point about extending the purges is well-taken, billtwocase.  I'll have to look into the details of the purge timing on the Carlin control; I have the impression that they are not adjustable.  I only get 30 seconds pre and 2 minutes post.  In fact I wonder if there's some relation of a too-short  purge with the "bark" sound I get on burner start.  There's a bark on start, about 10 or so seconds of somewhat louder than normal combustion noise, and then it goes normal (fairly quiet) for the rest of the cycle.  I didn't notice this with the old Weil-McLain negative draft boiler.  Or maybe there's a post oil shutoff drip going on that causes the bark?  There is of course a solenoid valve in the fuel unit that shuts off the oil during the purges.

billtwocase

is there

any oil leaks at the burner? Not sure why when it's pushing that you would have an oil smell coming from the transformer area. If it is leaky, it should be fresh air and not an exhaust or oil smell

Pete_in_Jersey

no oil leak I can find

That has had me puzzled as well. Theoretically it should be nothing but fresh air at that location. I've concluded there must be some kind of turbulence in the wheel/electrode/blast tube area that must backmix some small amount of downstream air back to the transformer hinge area, where it can leak out. The small amount of leaked air there smells like oil during the pre-purge, and starts smelling more like exhaust once the burner's running. Your comment on longer purges needed also fits in with post-shutoff oil drip being a contributor. I had installed a tee in the pressurized 1/8" oil line with a pressure gage (and shutoff 1/4" ball valve for the gage itself) to check pressure any time I like. This assembly holds more oil than the original 1/8" line, even with the gage valve shut; this oil is available for dripping out the nozzle after fuel unit shutoff. I doubt the engineers at Carlin have done computational fluid dynamics modeling to see if there's any backmixing back to the transformer area. In any case, simply sealing the area (as I did with silicone) would seem to be a prudent course of action, as any leaks will change the air/fuel ratio. Just leaving the transformer hold-down screws loose to leave a bigger air leak can make the flame rich by leaking a part of the combustion air to the basement.

icesailor

Gaskets:

This 4" intake fitting, is it something that Carlin makes that fits between the pump and the housing and you adjust the air with it? How does it finally vent through the building? Does it have some sort of a concentric fitting? It almost sounds like cross contamination to me. And that louder sound when it starts and sounds for a moment or two, and then quiet down and run smoother, that is the sound of the ignition spark dropping out.

I've never tried this but I will someday. Can you drill a hole in the intake piping and do a combustion analysis of the intake air? See if there is any CO, CO2 or smoke in there. Cross connection contamination is a real problem with direct vented appliances.

Is the intake and exhaust close to each other in the termination? "Sally goes round with Rosey". All the Carlin's I ever worked on were fine with back pressure.

The pre-purge, post purge timing are printed on the control. It will say something like 15/15/120. Meaning, 15 seconds pre-purge, 15 seconds trial fire, 120 seconds post purge. They are not adjustable.

icesailor

Pressures:

Another thing,

If the smell starts up after the unit shuts off, and the house is tight along with the cellar, you can get backward air flow if you have a chimney upstairs or any device that is making draft that is leaving the house. If a house is tight, Mother Nature gets very upset and will find a way to make things equal. You could have an unfinished bathroom in the cellar that is not connected to the sewer but has a vent running through the roof and a open drain. The draft in the plumbing vent will suck that air back through that boiler exhause so fast, you wouldn't realize that it was happening. That's why CO and non sealed combustion gas appliances are so dangerous.

Seen it, dealt with it. 

World Plumber

Pump seal

Have check the pump seal? Are you sucking oil into the fan and pushing that out? That should be the only air coming out the gasket area. Also check the solenoid valve for leaks. Seen a lot of them leak.

Pete_in_Jersey

all good questions

Icesailor - yes, the air inlet adapter is a narrow Carlin box with a 4" round inlet that directs the inlet air into the burner. The air/fuel ratio is adjusted by adjusting an opening more or less closed, just like on the old negative draft burners. This throttles the suction opening to the squirrel wheel. There's a 4" vacuum relief tee just upstream of the Carlin box that will open and allow basement air to be sucked into the tee's branch (and then into the burner) in case snow covers over the air inlet slots outside the building at the concentric direct vent device and starves the burner for air. No air is coming out of that device. Two completely separate runs of ductwork carry the inlet air from the concentric direct vent device to he burner, and the exhaust gases from the boiler breech to the concentric direct vent device. So the only place there could be cross-contamination is at the direct vent device going through the wall. It's brand new, but I know that doesn't guarantee anything. So the suggestion of analyzing the combustion air on the way to the boiler is a logical way to tell. Thanks. And thanks for the ignition spark info. There's nothing that could likely backdraft gas into the house, boiler running or not.



World Plumber - 2 more possibilities. It's brand new equipment, but again, that proves nothing. Thanks.

Pete_in_Jersey

you guys are good

I poked a hole in the air inlet tube and put an O2 analyzer in there last night. As the burner ran, the O2 dropped to about 19.5% and held there. This tells me that here's a cross contamination leak between the exhaust and the inlet at the direct vent poke-through-the-wall, or more likely, that the exhaust is simply bouncing off the ground and getting sucked into the air inlet. The air inlet holes suck directly from the sides of the direct vent device outside the wall, and the exhaust blows straight down, about a foot and a half off the ground. The inlet and outlet are literally inches away from each other. "Sally goes round with Rosey", as icesailor says.



Also now I notice the smell seems to change depending on when in the cycle the blower's running.



Of course a chimney wouldn't have this problem. Leaving the 4" inlet open at the burner and sucking air from the basement is not an option, as the inside-the-boiler stink comes slowly wafting out that inlet when the burner's off and there's no inlet air duct hooked to it. I've never had a boiler open that didn't smell, so this isn't surprising. I could disconnect the 4" air inlet from the direct vent and pull air from someplace else outside, though that would get rid of the air inlet preheating by exhaust in the direct vent, which ups effiiciency (probably ever so slightly).



I'm still thinking the silicone is the best option here to make it a really sealed system.

World Plumber

move the intake

I have a customer who used those terminations. He has all three intakes blocked off and put intake. vents on the other wall around the corner from the exhaust good chance that was the reason they did it.