Signs of condensation in and around boiler - Concerning?

Sweet_Lew

All,

Was poking around the boiler tonight and noticed signs of condensation and rust inside the draft hood. Upon further inspection I noticed what looked like rusty water stains on the bottom of the unit as well and on the concrete slab the unit sits on. The exhaust flue pipe is 4" and my hot water heater connects into it as well. The boiler is 10 years old but I'm wondering if I need a complete re-eval of the entire heating system and chimney. This can't be normal can it? Is a 4" flue too large? Attached is a pic of the system:



Thanks,



Lew

Brad White

A couple of thoughts

Your system looks like it was once an old gravity HW system, correct? You have a single diaphragm tank in the photo and those are rarely sufficient for water volumes inherent to older gravity HW systems. (My own house has converted gravity HW and holds 80 gallons. I have two #30 tanks with room for a third. The pressure rises from 18 psig cold to about 24 when hot. If your system is similar but you have one tank, you may well be hitting 30 psig and lifting the relief valve.)



I am surmising with the recent colder weather that your water is as hot as it has ever been and hence at its maximum volume, coupled with a possible loss of expansion tank charge.  What is your system operating pressure, cold to hot?



I would put a "witness cup" (a term I owe to Mark Etherton), under the relief valve pipe to see if that is the source of the water.



The rust inside the flue? Could this be older stuff? All boilers are condensing boilers for a period of time and I have yet to see any atmospheric or other boiler with galvanized flue pipe that did not have at least a surface dusting of rust. If you DO have standing condensate, visible moisture, I would ask what your water return temperature is vs. the supply temperature. It may also be excess air, cooling the flue gasses, but that is a stretch with atmospheric boilers, they already draw all the air they need.

Sweet_Lew

Thanks for the reply

Brad,



I'm pretty sure it is a converted gravity system. Currently, the pressure is set to 15 cold and gets between 21 and 25psi when hot. Temp limit is set to 180 degrees F. Also, the PRV has never gone off.



I'm hoping the rust is when the previous owners had the house. I'm now thinking the flue is actually 6" (I need to find the old receipt from when the liner was installed). Regardless, I'm thinking the flue could be too wide in diameter causing an insufficient draft.

Brad White

More observations

The flue looks to be connection size but from the photo 5" or 6", hard to tell. What is the BTUH input? That might give me an idea.



But something else I noticed, maybe not directly related to your condition. In that photo, did I notice the HW heater vent angling down into the boiler flue? That is a no-no, the pitch should be continuously upward and preferably vent above the boiler flue with a separate entry. It looks like they ran out of "H" dimension



As far as insufficient draft, if you do not have a sensitive manometer (I use either a Dwyer 477 or an Energy Conservatory DG700), you can always use incense. A strong draft will pull smoke like a string, even through an old screw hole. Best bet though is to actually measure it.

Sweet_Lew

I'll check tonight

Brad,

It is 6". I was getting my bathroom exhaust fan ducting mixed up (just installed new 4" ducting for the fan). I'll double check the piping of the hot water heater, but I think you are right. I'll look into getting that redone. Good call on the incense. I'll have to pick some up (long past my college hippie days =P )

Lew

Brad White

I hope

that the 4" bathroom vent is in no way connected to the flue system!

If you get those confused, maybe your college hippie days are still a-happening!

Pass the bong, please. Dude!

Sweet_Lew

HAHA!

Nope..It's not connected to the flue system...

gennady

water stains

your boiler probably condense at start. when return temperature of water from heating system drops below 132F. to eliminate this you might install bypass or primary secondary loop arrangement

Sweet_Lew

Just gonna let it go..

Thanks for the reply. I just had my circ pump seize on me. That was a chunk of overpriced change from my heating pro. At this point, I think I'm gonna let the system do it's thing until is breaks and then do a complete re-design with a high efficiency unit w\dual zones.