Questions on chimney liners

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How effective are they at eliminating moisture problems and how to know whether you have a problem. It is needed.

In early May this year I had a Buderus G115/4 installed ( oil ) and hooked to my existing chimney. I have no moisture problems so far but since it was installed when it was already warm I have not tested this very well yet. My house was built in the 1950's with a brick exterior / clay lined chimney with 3 sides exposed to the outside. It has dual flues one for fireplace and one for the burner. The chimney is approx 20 feet high. bottom to top.
I had a chimney sweep come to install caps on the chimney which I feel I need . However he recommended that I have a stainless liner installed and he feels that in the winter I will likely have a moisture problem. He said all of the newer more eff boiler should have a stainless liner installed.
I have called a few other installers and am getting mixed answers whether the liner is needed. I appreciate your comments and help.
The combustion test that was done at start up of the new system showed an efficiency of 86% and flue gas temp around 400 deg.
Also he said after the liner is installed the system needs to be adjusted. What adjustments are needed?
thanks

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Thank you Hattersguy good info

Jack

Exterior chimneys are the absolute worst. Given that yours is an exterior chimney you are correct in being concerned and I think the sweep is on the money on this. How large is the liner in the flue? If you look at a 6" round breeching on the boiler it is about 30 sq". An 8x8 tile is about 56sq" net and it loves to suck up the heat. It's the old adobe principle. As well, when a gas expands, it cools, so a larger tile exacerbates the situation.
You will get better operation with a properly lined flue. The unit will operate more reliably with smoother light offs and cleaner where it can establish good draft quickly and get beyond the "wet-time". When back in the 90's Brookhaven Nat'l Labs evaluated oil flues the comment from the lead engineer on the project was that regardless of configuration the thing that had the most positive impact on vent performance was an insulated vent connector (from the boiler breeching to the vertical portion of the chimney).
If it was my house and my new boiler I would re-line with (assuming a straight chimney with no offsets) a smooth stainless liner. Actually if it would clear, I'd use Selkirk DS or Duravent DSL. That is an SS L-vent (approved for oil) double wall so it is insulated. I would run it all the way to the boiler.
I just spent some of your money there, but you have to remember that this is a "system". That system starts at the fill pipe for the oil tank and includes your baseboard or whatever distribution system you have and the system terminates at the chimney flue.
Line it! You will be happy that you did!

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Thank you Jack for your help. The sweep has a lot of experience but not too good at explaining the technical aspects. This will help making a decision.

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Thanks again Hatterasguy. That was one of the questions i had. I will take my time to decide. It maybe a good idea long term but this explains the different opinions I got from different installers. It was good to get the chimney comparison that you made and your experience with your system.

Jack

Back in '91 when the efficiencies of gas equipment were mandated to a minimum of 78% the whole chimney lining industry took off, aside from that which had been done for solid fuel burning appliances. It was a lot of fun doing the trainings and having the conversations on what was happening in masonry chimneys. No one wanted to hear it, but the evidence was irrefutable and over time each subsequent edition of NFPA 54 became more and more stringent on the requirements for re-lining masonry flues. I was representing Z-Flex, Metalbestos and Tjernlund in those days so I had a really good view of what was going on.

I applied and was accepted to be a member of the NFPA 31 Committee in, I think it was '93. Closely following that was when the Brookhaven report on Oil Fired Vent System Operation came out. Richard Krawjewski and John Strasser were the project engineers and they did an exhaustive study on the operation of chimneys on oil fired equipment. Their findings, which strongly supported re-lining, were reported to the 31 group and ended up being put into Appendix E, so as to not become a part of the code. No one, almost no one, in the industry wanted to add costs to oil fired installations due to competitive fears, so E is still an appendix item regardless of what the Brookhaven report said. The sizings in "E" are right on the money from those I have spoken with who have used them over the years. I solved more than a few problems actually relining a couple well known oil systems using 4" pellet vent, and the systems purred.

Oil systems do condense. As HG has noted the purpose of a liner is to reduce the "wet time" in a flue. Every system on a cold start will condense. Yes, you do want to have a flue designed to heat up quickly and SS will certainly do that while the mass of masonry MAY not. Every system has a personality. How is yours doings? A properly designed flue , in my experience, does improve light-off and does , or at least can, improve efficiency. Establishing good draft faster, by having a warm flue gets the draw going through the appliance faster, sooner and better. As with all combustion equipment you don't have pristine operation at start-up. If you are going to get any dirty combustion it is then. Over a long season if that condition lasts longer due to slow draft the small amount of soot finds its way onto the interior of your appliance and it sticks. It only takes a few mils of scale to reduce heat transfer. Of course you will never notice it because that will reduce heat transfer and your stack temp will go up and the chimney will operate better. Problem solved;) A high mass, oversized masonry flue will not operate as well as a properly sized low mass SS flue! High mass oversized masonry is 11th Century technology venting 21st Century appliances.

Net/net, you have a professional sweep on site examining YOUR chimney. Every system has its own personality. You just hope yours is more Jeckyl than Hyde. Evaluate the operation of your system.

It was pointed out, and thank you Kurt, that my model numbers on the double wall were incorrect. Duravents is a DVL. I went to Selkirk's site and was so confused I gave up looking, but was informed it is a DSP. My apologies for the error.

Happy Heating!

Robert O'Brien

400* net stack on a 115/4? Overfired,baffles out or both.

Robert O'Brien

That's high,with all the baffles in and at max firing rate, 280* is average

Jack

HG, no, I cannot put figures on this. I also cannot and will not say you are wrong. You have a lot of experience, daily, that I do not have. The experience I do have is that no one ever calls the rep unless it is a catastrophe, and I saw a lot of them. Some I was able to assist in fixing. Some not! In my opinion, when a customer makes the investment in a new oil or any other type of appliance they are entitled to a proper and comprehensive discussion of all aspects of the "system". Everyone looks at the chimney and says, "oh, it's the chimney, it's ok." Well, frequently it isn't but it gets swept under the rug. The "payback" is that a customer should have the confidence that for the money they will get the best operating system that will last a long time. Not discussing and honestly addressing venting issues, especially with an exterior chimney, is just wrong.

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I'm the original poster. I really appreciate all the posts. An additional question? For the liner install one sweep said he just bends the 5 inch flex stainless 3/16 inch at the bottom to feed through the wall? Not sure if that allows condensation to come into the inside . Another sweep said he uses a 90 tee at the bottom and removes some material at the bottom if needed to fit the tee.
What is the correct way. Your input on this is appreciated.
So far I have not found anyone that looks at the whole system. The heating help forum is my source.
I'm trying to do the correct thing but the info I get is all over the place.
Thanks

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bink again. I checked the tag from the original set up. As comments suggest it appears the stack temp was 300 degrees not 400 degrees as I had in the original post. I will have it rechecked to make sure.