Water (condensation?) coming through vent on vitogas 050 - pictures

cmattina

I moved into the house this year (first home) and this is my first winter with the boiler. It was installed in 2006. I did have it inspected when i moved in (august, 2015) and it checked out alright. It is a two story century home with a brick chimney that runs up the side of the house. The hotwater tank and boiler both vent out this chimney, and living room gas fire place has it's own vent.

Today is the coldest day of the year (-30 with the windchill).

However, i just noticed there is water coming through the vent and making it's way to the floor. I have no idea how long this has been happening, but it must have happened before, and/or for a long time because there is rust build up in the spot it is coming in.


It could be coming from the gas hotwater tank that shares the main vent? Or perhaps chimney condensation? Or both? Or, just the boiler.

I took a picture of how it is vented as well as signs of moisture coming back down the vent for some time (no pictures of the rust or water on the floor though, but it is there).

cmattina

second pic

cmattina

chimey vent... looks like some snow beside it... No one else's has snow buildup like that?

Edit: it is possible that the "snow" build up is actually frost, and the frost may be coming from the vapour, then melting and coming down my vent...

Jamie Hall

Most likely condensation. It's surprising how much water there is in the flue gas -- if memory serves, on the order of a gallon of water for every gallon of fuel. Cold chimney such as yours? At least some of it will condense and it has to go somewhere!

SWEI

That's condensation residue, and it will eat your flue pipes. A properly trained tech with a combustion analyzer can help
http://www.stopcarbonmonoxide.com/index.cfm?p=find

Ironman

Neither the boiler nor the water heater should be connected to a masonry chimney on an outside wall unless it has a properly sized, insulated, stainless steel liner. Newer, high efficiency appliances have much cooler stack temperatures than the previous ones and flue gas condensation will occur as you have discovered. The condensation is acidic and it will rot your metal flue piping and attack the mortar joints in the chimney.

Two other things to have checked:
1. Make sure the burner manifold gas pressure is correct to assure it's firing at the right rate.
2. Make sure the boiler is maintaining at least 140* return water temp when running.

If either of these two are too low, flue gas condensation will occur.

CMadatMe

For proper operation of the Vitogas boiler, all
products of combustion must be safely
vented to the outdoors, while ensuring that
flue gases do not cool prematurely.
It is critical that the chimney system be
properly designed and sized to handle the
relatively cool flue gas temperatures which
the Vitogas boiler produces.
Flue gases which cool too quickly and
produce condensation lead to damages if
the chimney diameter is too large and the
chimney system is not well insulated.
If a calculated chimney diameter lies
between two values, the larger diameter
should be selected.


Chimney should have been lined plain and simple..

cmattina

Okay, thanks for the advice everyone.


Couple things to note:

- The condensation dripping has stopped, and it has been dry
for a few hours now.

- The chimney looks like it was rebuilt not TOO long ago. and the
pipe coming out the top of it looks quite new (i would guess no
more than 20 years, possibly 5-10 years.

- I have seen those insulated flues, and with the temperatures we
have, it wouldn't be enough (-30), unless it some sort of super
insulation that defies the laws of thermodynamics

- My CO2 detector in the basement has not gone off and i can see exhaust coming out the chimney.

cmattina

Chris said:

For proper operation of the Vitogas boiler, all
products of combustion must be safely
vented to the outdoors, while ensuring that
flue gases do not cool prematurely.
It is critical that the chimney system be
properly designed and sized to handle the
relatively cool flue gas temperatures which
the Vitogas boiler produces.
Flue gases which cool too quickly and
produce condensation lead to damages if
the chimney diameter is too large and the
chimney system is not well insulated.
If a calculated chimney diameter lies
between two values, the larger diameter
should be selected.


Chimney should have been lined plain and simple..

Thanks Chris. Although i don't know for sure whether it is lined, i would bet it is, just looking at the quality and condition of the chimney and stainless pipe coming out the top. However, it is possible the installer put on a pipe that was too large/narrow and the height of the chimney is too much for the little vitogas 050 to push out???

I imagine the height of the chimney was fine for the old boiler, but i have read that with newer high and mid efficiency boilers, chimney can be too tall for them to push out all the moisture...

CMadatMe

Use approved vent materials only. For venting purposes,
a B-vent may be used.
With this boiler installation, it is recommended to install a
corrosion resistant approved liner within a masonry or unlined
chimney. Observe and follow local rules and regulations.

When it comes to venting always go by the letter of the installation manual..

SWEI

cmattina said:

I have seen those insulated flues, and with the temperatures we have, it wouldn't be enough (-30), unless it some sort of super insulation that defies the laws of thermodynamics.

No need for anything magical -- a chimney full of perlite will probably cover it. In that climate, you really must have some insulation. With 375°F or hotter air entering it, keep what you can...

CMadatMe

cmattina said:

Chris said:

For proper operation of the Vitogas boiler, all
products of combustion must be safely
vented to the outdoors, while ensuring that
flue gases do not cool prematurely.
It is critical that the chimney system be
properly designed and sized to handle the
relatively cool flue gas temperatures which
the Vitogas boiler produces.
Flue gases which cool too quickly and
produce condensation lead to damages if
the chimney diameter is too large and the
chimney system is not well insulated.
If a calculated chimney diameter lies
between two values, the larger diameter
should be selected.


Chimney should have been lined plain and simple..

Thanks Chris. Although i don't know for sure whether it is lined, i would bet it is, just looking at the quality and condition of the chimney and stainless pipe coming out the top. However, it is possible the installer put on a pipe that was too large/narrow and the height of the chimney is too much for the little vitogas 050 to push out???

I imagine the height of the chimney was fine for the old boiler, but i have read that with newer high and mid efficiency boilers, chimney can be too tall for them to push out all the moisture...

See attached as a guide.

SWEI

Chris said:

With this boiler installation, it is recommended to install a
corrosion resistant approved liner

That way, you can take advantage of the Vitogas' ability to handle low return water temps. Take care of it and that boiler should last a generation or two.

cmattina

SWEI said:

Chris said:

With this boiler installation, it is recommended to install a
corrosion resistant approved liner

That way, you can take advantage of the Vitogas' ability to handle low return water temps. Take care of it and that boiler should last a generation or two.

Hi SWEI,

I was just coming here to comment that my water temp, as far as i know, has never been higher than 130, whereas somehere said to make sure it gets to atleast 140.


Curious if you are saying the vitogas is meant to heat water at a lower temp... i assume for energy savings?


Oddly, i've got now more issue with condensation dripping down... i am not sure if there is any up in there though...


You seem to be familar with the vitogas... i have some series rust in the top of the boiler where it vents out... I have to assume this is not normal, and i guess is a result of moisture?


Maybe i am not getting a great burn? i have noticed more orange in the flames than i'd like...

aircooled81

These guys know there stuff, wish i knew that much about chimney venting!
Picture when your appliance is off, it cools down. Moisture in the air, cold dense air wanders down the stack. Your appliance turns on, moisture is still in the air, expanded. It (flue gas) wanders up the stack and is touching cold flue pipes. It doesnt want to stay moisture, it wants to cool into water, or condense into condensate. That weighs more than flue gas and drips back down the flue...
I meen, i guess thats how im picturing the need for well insulated chimney and flue stack?

gennady

This boiler is condensing. white stuff is a sulfur. What type of control installed on this boiler?

In general you need to set up boiler cold water protection, meaning that circulator will not start until boiler temperature will reach 140F.

Another way of boiler temperature control on low side can be diverter valve or just simple bypass.

Boiler limit must be set to 180F, meaning that boiler stops combustion when water temperature reach 180F. If you have low temperature heating system , like radiant, you need mixing valves installed. In any case boiler water temperature must not be lower than 140F.

SWEI

I was told (some years back) that the Vitogas castings were made from a special gray iron which, together with some careful geometry, allowed it to tolerate lower return water temps than other CI boilers. The flue would have to be corrosion resistant, to which Viessman alludes in their docs. I'll bet Chris has the backstory.

CMadatMe

Venting off the boiler should have been a min of B-Vent. Boiler get you condensing in the chimney. You are starting with lower flue gas temps from the get go. That's why they make installation manuals and tell the installer certain ways are recommended. Boiler can handle less the 140 degrees as far as the iron is concerned. Wouldn't be concerned over water temp effect on the boiler itself. Issue is the chimney. Venting off the boiler looks like 7" so that's a 140,000 btu/hr Vitogas or higher. I'm sure that water heater isn't helping either. What size is the liner? Max water temp is set 167 at the factory and they recommend designing for a 158 degree supply water temp. I'd also consider this a mid/low mass boiler depending on the size. The 200,000 Btu/hr boiler only holds about 7 gallons of water. As an example a Vitodens 200 B2HA150 (530,000 Btu/hr) Wall Hung Condensing holds 4 gallons of water.

gennady

Vitogas is not a condensing boiler. All condensation must happen in the atmosphere after of the chimney. I attached some clips from boiler manual.
Vitogas is category 1 appliance, venting cannot be under positive pressure and condensation must not occur in the chimney. See attached chart.

gennady

Vitogas is category 1 appliance. Venting cannot be under positive pressure and no condensation can occur in the chimney.

cmattina

Okay,

Some of this stuff is getting over my head.

I had some typos before.

To clarify, there has been no more moisture (it was just that one night).

A difference between the diagram Gennady supplied and what I have is: my circulator is on the return, and my city water, backflow preventer, and expansion tank are attached to supply. I have no bypass.If i were to install a bypass would I have to change everything over to match the diagram? Would a bypass even solve my problem...

At present, my damper is set to hold open and there does not seem to be cold air coming down through the vent (surprisingly).

I was wondering how I can change my circulator to only start after the temp reaches 140. I feel this may heat the exhaust air better so that it has more force to escape up the rather tall chimney and then condense in the atmosphere. I personally do not know anyone with such a tall chimney paired with a mid-efficiency boiler/furnace. Everyone i know with new HVAC have a side vent.

I have no idea my actual vent diameter in the chimney. It is sealed up pretty good and I'd rather not start messing around with it.

cmattina

Here are some pics. As one can see there is, what I would call substantial rust for a 9 year old boiler...


The previous owners replaced a part, I believe the control panel (or whatever it is called) last year. All I know is it was around $500 or $600

Perhaps looking at my cic pump someone can let me know if it is set correctly?

CMadatMe

gennady said:

Vitogas is not a condensing boiler. All condensation must happen in the atmosphere after of the chimney. I attached some clips from boiler manual.
Vitogas is category 1 appliance, venting cannot be under positive pressure and condensation must not occur in the chimney. See attached chart.

Never said the boiler was condensing. Said, it will get you condensing due to cooler stack temps and thus why venting should have been a minimum of B-Vent.

gennady

cmattina said:

Okay,

Some of this stuff is getting over my head.

I had some typos before.

To clarify, there has been no more moisture (it was just that one night).

A difference between the diagram Gennady supplied and what I have is: my circulator is on the return, and my city water, backflow preventer, and expansion tank are attached to supply. I have no bypass.If i were to install a bypass would I have to change everything over to match the diagram? Would a bypass even solve my problem...

At present, my damper is set to hold open and there does not seem to be cold air coming down through the vent (surprisingly).

I was wondering how I can change my circulator to only start after the temp reaches 140. I feel this may heat the exhaust air better so that it has more force to escape up the rather tall chimney and then condense in the atmosphere. I personally do not know anyone with such a tall chimney paired with a mid-efficiency boiler/furnace. Everyone i know with new HVAC have a side vent.

I have no idea my actual vent diameter in the chimney. It is sealed up pretty good and I'd rather not start messing around with it.

You will need to replace aquastat with dual aquastat honeywell L4081B and wire circulator into this control.

aircooled81

Thats a bummer, what are the chances that flue pipe in the chimney looks like the flue in the boiler?
Gennady, I think, If you were able to let the boiler warm up to 140, ther'd still be some cool water returning when the pump kicked on. Is most of the condensation avoided because the boiler comes up to temp faster this way (with a temp switch for the pump)? At what point would a mixing valve be suggested too?

Just noting from OP's boiler detail previously...
If you ever take a swing at the piping, think about moving the make up water and expansion tank to the low side of the system, not the supply. If you really get elbows deep in piping and pump cycle, think about moving the pump to the leaving side of the boiler.

gennady

aircooled81 said:

Thats a bummer, what are the chances that flue pipe in the chimney looks like the I think, If you were able to let the boiler warm up to 140, ther'd still be some cool water returning when the pump kicked on. Is most of the condensation avoided because the boiler comes up to temp faster this way (with a temp switch for the pump)?

cold water return will mix with boiler water and if temperature drops below setpoint, boiler will stop pump and heat up next portion of water with no condensation. On cold start-up there will be few times when pump stops, depending on firing rate and water content of the system.

diverter(mixing) valve is just an alternative to dual aquastat.

captainco

I always wonder when someone states that the flue temperature of new boilers is lower than old ones, if they ever measured the flue temperature above a drafthood? With 40% to 50% dilution air the flue temperatures of drafthood equipment are almost always cooler than the newer induced draft, with no dilution air.
As draft increases, the induced draft boiler flue temperature gets warmer while the drafthood one gets cooler.

When boilers and water heaters are connected to flues, why do flues cool down during the off cycle? They store heat! Yes, if the mechanical room is negative pressure then cold air will come down the flue. That is a combustion air problem not a flue problem.

Keeping a circulator off until the boiler reaches 140 degrees is certainly one way to cause thermal shock, by getting the boiler hot and then bringing back cold water from the loop. The pump should actually start before the burners come on.

How can water heaters operate with incoming water of 45 to 50 degrees and seem to work okay and yet a boiler with 100 degree return water can't?

Flue condensation is rarely the flues fault. Underfiring equipment, improper combustion air(allows mechanical room to be in a negative pressure) are main causes. In the case of induced draft lack of proper post-purge is another contributor.
The real mind bender is that flues that are smaller contribute to condensation more than flues that are bigger. If the flue gases move through the flue faster and make less contact with the flue surface, they maintain their temperatures much better. More than once I have had to recommend using larger B-vent or a larger Liner to minimize the cooling of flue gases and reduce condensation,

Measure the flue temperature on any drafthood appliance above the drafthood, when the draft in the flue is over -.02" and you will rarely see a temperature above 300 degrees, which is the lowest it should ever be on induced draft equipment, whether a boiler or a furnace.

Too many smart people here to allow hearsay to influence decisions when simple measurements prove otherwise. My education began many years ago after I got tired of the same answer to my questions: "Because everybody says so!"

cmattina

Just in case someone in the future of the internet comes across this question, i think i have had the question solved.


As far as i can tell, the previous owners had never had it (the burners) cleaned in 10 years (odd as they had to have a part replaced on it just a couple years ago).

So, the burners were not getting hot enough, and i think that is why condensation was coming through. The condensation rusted the collector box to the point it needs to be replace ($500 for a steel box?).

Luckily, the rust on the actual heat exchanger was just just superficial and that looked okay after getting cleaned up a bit.

Of course it is still august so i will have to wait and see if it totally solves the problem.

Perfect example of how preventative maintenance saved money in the future.

gennady

captainco said:

Keeping a circulator off until the boiler reaches 140 degrees is certainly one way to cause thermal shock, by getting the boiler hot and then bringing back cold water from the loop. The pump should actually start before the burners come on.

There is no thermal shocks, cold water protection designed to works at the cold start. As soon system warms up there is no need to stop pump, return temperature is 20F less than supply, and well above condensation.

gennady

cmattina said:

So, the burners were not getting hot enough, and i think that is why condensation was coming through.

Burners problems are just consequence, not a root of the problem.