excess condensation in flue on Viessmann

V8toilet_3

Thanks again for the input. I cleaned all the crud off the cabinet a while back, and there is not a drop onit now. Odd how it can run for weeks with no issues, then have periods where it is condensing like crazy. Must be just the right conditions to set things off. I do have a min temp of about 140F set to accomodate a hydro air coil on the high temp circuit. Had to do that because on mild days the boiler temp would dip so low, we could not get heat on the second floor (heated by hydro air). Speaking of wich, the circ pump on circuit 1 pumps water up to the coil all the time. Our programmable tstat on the second floor controls when the blower runs. When the blower is off, hot watere is pumped through the coil, and I assume this adds to the stanby losses. What do you think of adding a relay to control the heating circuit #1 pump to only come on when the blower is running? Do you think it would add enough efficieany to make it worth while?? I guess I would also save some electricity, and wear on the pump, right?

V8toilet_3

Hello. I've got a Viessman oil fired boiler that occasionally has water leaking out the elbow joints of the flue pipe, The water than drips onto the top of the horizontal DHW tank the boiler sits on, and leaves bedind a crust that looks like rock salt mixed with tar, When I first had it inspected during install, the HVAC tech who was not familliar with Viessmans could not get over how low the stack temp was. He said he had to fully insert the probe just to get a reading. Viessman literature mentions drilling additional holes in the fire chamber to raise flue gas temp, but it slao says each hole reduces efficiency. I do not get the water dripping issue all the time, seems to be related to outdoor temp. Is this due to the boiler water temp being so low during mild weather?? I should also mention that the basement is unconditioned space that stays at about 50 degrees most of the time, but also has high relative humidity, especially in the spring due to high water table. Another possible factor is the flue/chimney setup. I have a triple wall stainless lined Duravent metal chimney that runs down the center of the house. Due to construction issues, the chimmney is not a straight shot. At the very top, there is a couple 22.5 degree elbows used to shift the chimney about 16" over from were it exits the peek to were it exits the fake chimney chase. The chimney manufacturer allows for this in the install specs. Due to critical position of 2 steel lolly columns, the outlet on the boiler had to be moved about 5 feet over from were we originally planned. This was accomplished with a couple of 45 degree ells, and an approximate 6 foot section of flue pipe rising away from the boiler towards he base of the chimney at about a 45 degree angle. The barometric damper is located about a third if the way up this incline, and installed horizontally. Most of the joints are sealed with high temp silicone. If all joints were sealed, could the water then run back into the boiler, promoting corrosion? Should I just forget about the efficiency loss and raise the flue gas temp via more holes in the chamber? Should I insulate the flue pipe??? wold it be better to install air duct to have combustion air be drawn from outside only?

trevor pierce, London Boiler Service

viessmann

I guess you have a Vitola, the decrease in efficiency from drilling the holes is minimal!, there is holes marked out in the back, you only have to drill out the material at the back of the exchanger and not the stainless! I tend to run insulated venting as close to the boiler as possible and will have the chimney insulated! With an unheated basement it must really leakout of the chimney! This can ruin your chimney and I would recomend getting this taken care of. Even if I would use a stainless chimney liner I would insulate the chimney! Have your guy check local codes on this, I'm up in Canada and codes may differ. It is very common to see a Vitola running in the very high 80% range to 90% I'm sure some of the guys here can input on the local codes and practice

Paul Pollets

Flue gas condensation

The boiler should never be dripping from the flue, or back to the boiler. This can cause permanent damage to the boiler and premature boiler failure. The venting to the chimney must be pitched 1/8" to the chimney and installed with a barometric damper. The damper should be within 2 feet of the boiler vent. The chimney should be insulated and be high enough to allow proper draft. The stainless combustion pot can be drilled to raise stack temps, per manufacturer's instructions. The burner must be re-tuned with a combustion analyzer to factory spec. The draft should be -.02". If you're using the Viessmann chassis burner, the stack temp should be 300-400 degrees. If the horizontal vent to the chimney is too long, there will also be condensation.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

V8toilet_3

Hello Paul, the venting is pitched, but greater than 1/8", rising as it leaves the boiler moving towards the chimney. The barometric is installed as you describe, and there really isn't any horizontal run at all. The overall hieght of the chimney is over 35 feet. The chimney is not insulated, but most of its length is within the heated building envelope, not on an outside wall, or in an exterior chase. I am using the Veissman chassis burner. I will be looking for a good tech ASAP. What do you think about insulating and/or sealing the flue pipe joints?

trevor pierce, London Boiler Service

vitola

The first picture is of a vitola I installed about 6 years ago, I cant ever remember the stack temp being over 240 deg f, it opperates a low temp and medium temp system with outdoor setback, the water temp can get very low and I have actually stood there with my hand on the chimney as it ran! I brought the double wall venting very close to the boiler! If you call the Viessmann number in your owners manual Im sure they can give you advice! Also atached is a picture of an install in europe where they will often insulate the chimney as much as possible! Hope this gives some guidence, they run on very low temps, call Viessmann!

trevor pierce, London Boiler Service

factory printout

Hay, if you look in your papers that came with the boiler you will see a factory test report with a small sheet attached to it, looks like a cash registar reciept, Viessmann test fires all of these! It may be helpful to look at this, it will have abreviations, stack temp, co co2, eff, fuel # etc, could be helpful if you post these results! It will be atached to a single sheet that will have some pen writing on it!

V8toilet_3

Hello Trevor. Like the photo of the install you did. Very nice work. Obvious you take great pride in your workmanship. I found my paper slip from the factory, not sure how much info you want. Fuel type: #2 oil, T air 78F, T Gas 191 F, O2 4.1%, CO 6ppm, NO 94ppm, NO2 3ppm, NOx 97ppm, CO2 12.6%, Efficiency 91.7%, losses 8.3%, Exc air 1.24. Then theres a bunch more on the sheet that slip is stapled to. Let me know if you think any of that would be helpfull to post.

trevor pierce, London Boiler Service

bump

trevor pierce, London Boiler Service

wow

Look at the numbers guys!!! 91.7% Efficiency! V8 toilet, you see the air temp going into this thing when they tested it, 78f! it was warm, and they have high efficiency, now imagine your cool basement air going into the boiler and draft diverter will lower your stack temp even more! The boiler room in the picture is only a boiler room so I keep it very warm, if it were unconditioned I'm sure it would be raining off that chimney when the control brings it down to low temp! I would have taken a different aprouch also, the Lvent would be down to the damper, or I may have ran all fuels chimney all the way! You can try replacing the vent with Lvent, drill out the holes in the back of the exchanger! Sadly, you may just have to adjust the minimum boiler temp to overcome the flue condensation! Not a big deal, do what can be done to chimney, drill exchanger and find the sweet spot where you are running as low as you can but not condensing in the flue! A thermometor in the stack helps for this, on the vitotronic you can select the space heating mode, use the round rotary dial to raise the slope(adjust room temp) and the control will bring the boiler water temp up and your heating teck can determine what boiler temp will work to stop the condensation! just remember, an insulated vent will keep this minimum temp lower, and be more efficient! when you guys determine the minimum temp you will need adjust the room temp (round dial on right)back to where it was, go to coding and set a boiler min! The printout is for other people on this sight, many are very smart and looking at the factory test and settings on this unit they will give you some very good insight! I'm sure there is guys here that can ask you the boiler room temp and stack etc and help you! DEW POINT OF OIL ANYONE?? I dont know this! Keep this page at the very front of the binder you got with the boiler, you may even want to laminate the thing! It gives anyone who goes there a starting point! It has air shutter adjust, turbulator, pump press etc! most guys will say they love to have this info when they go to a job!