Thanks champipple and paulbmfor the inputs. I was away for two weeks. I had a contractor come in and another guy from a heating company this past weekend. The contractor wanted to put another wall up where the flu connects in an attempt to keep the flu where it exits the wall as close as to the outside temperature. This other guy from a heating company said to he would like to use double wall flue since he thinks the condensation is occurring where the flue exits into the wall. Now I understand what they are attempting to do and it sounds right to me (since i really don't know that much) but which solution would work the best? Another detail I would like to add is the furnace and two water heaters are enclosed inside of a 5' by 10' room. Thanks! Barry.

National Company! I'll guess Delta Mechanical. It all depends upon the guy doing the work. You should not have 5" on the vent connector. You should have 4" B-vent. The inch diameter you pick up will allow for proper grading of the flue. Your best bet on liner will be to install B-vent all the way down. You should have a bottom capped tee at the bottom of the stack as a drip leg. Yours is the worst condition for a Category I furnace, long vent connector and exterior chimney. If you go with a chimney sweep for the liner, as I said, chick out the Chimney Sweep Guild for a "real" contractor. You are correct about getting taken on this. There has been all kinds of fraud in this field. Perhaps it would be best to make the installing company come through on this. MAKE SURE, if you have them do it with B-vent that they screw the joints together with screw that does not penetrate the inner aluminum liner. A seemingly small but important detail. Also have them use a metal tape on the joints. They can drop the tee and vert portion into the flue and work back to the furnace, finishing with an adjustable length at the furnace. I am glad that you liked the salesman, but I would not let him off the hook on this. If he is a good guy you can help him become better by insisting that he come out and look at the system. You never install a Cat I furnace where a masonry chimney is going to be used. It is "the" reason to go to the condensing furnace using PVC for the side wall venting. As well, you pick up another 15% efficiency. You will be helping this man if you have this conversation. Nationally, once you cross the Mason-Dixon condensing furnaces are 95+% of the market. As you move south, the view is the heating load is not as high so, why buy the more expensive (efficient) equipment. Net/net, regardless of intent, you got stiffed here by nice but not well informed people and your inspector pencil whipped the permit. Perhaps that is a bit tough. they did fail the inspection initially. Salti, heck, we don't argue. I enjoy reading your posts. In my experience, if you were hitting 80% with the old furnace you "grabbed the brass ring", unless it was an oil furnace and the better brands have almost always hit the 80% mark. Is it oil? If it is gas and old, I really am surprised. The reason the codes changed since '91 is that by being mandated to deliver a min efficiency of 78% up from those 60% figures is that by putting the heat into the house there was less energy available to drive proper venting of the new appliances in masonry. Proper venting meaning getting the flue gases out as a vapor and not having them condense (approx 3.2 Ph) on the walls of the flue. You can hide a lot of design issues with a high stack temperature. With high exhaust temps you gained velocity. With 78% you didn't have a chance. Even at that, it was interesting seeing the code changes over the years. Every four years with the new edition of NFPA 54 the restrictions became more and more stringent until about 10 years ago they finally said, "masonry chimneys do not work and do not use them". Also, be aware, if you are hitting the 80% combustion efficiency" that is not remotely close to system efficiency. You have probably seen my fairly frequent posts on googling, "doe duct leakage". If you want to get the best out of your heating dollar, seal the duct system. Residential duct systems in the US are terrible. It is the "crazy aunt in the back room" that no one in the industry wants to talk about. It is a big deal and it is finally coming to light. What I have always said is the unitary manuf (Carrier, York, Lennox, Trane, etc) can put all the technology they want in the box. They simply cannot deliver it…due to duct leakage Happy Heating!

Navien is a well established manufacturer with a good reputation world wide. I see them extensively used in commercially designed residential applications where many multiple boilers are installed providing staged capacity and redundancy. Are you aware of any class action law suits against Navien that have been successful? How would you know whether the ‘terrible reputation’ is the result of ‘terrible installation' or not? We know the definition of ‘insanity’. Doing the same thing the same way repeatedly and expecting a different outcome. That is what I expect is going on. Modern hydronics consists of 2-discreet component systems that each have to be designed and tuned for maximum efficiency with the distribution system also designed and tuned for comfort and then mated to each other. This is likely what’s not happening with the failures you’re eluding to. Something else is happening there to cause these failure, like a poorly designed distribution systems that results in low efficiency, short cycling, corrosive chemistry in flue gases or heat exchangers, improper ∆T between supply & return fluids, improper selection or setup of circulators, buffer tanks or (no) hydraulic separators, lack of proper controls, programming and monitoring, as just a few examples. Replacement ‘conditioned’ pre-mixed system fluids can be stored in liquid reservoirs feeds with low-level monitor alerts to ensure replacement fluids are of the right, non-corrosive chemistry. The days of straight up tap water as a replacement fluid is long gone unless you like corrosion, scale and expensive service calls. Yes, if serious algebra is part of basic arithmetic, then that’s all that’s needed. If California is doing something else - that’s just fine! IMPO SR

I thought we agreed that we were not going to limit the discussion to the climate of Katy Texas? Well the OP who started this thread made it sound like he lived near me... which would mean using my climate numbers as opposed to somewhere else. I don't service areas outside my climate so why on earth would I entertain this idea of yours? (I offer advice on occasion but that is all it is --- professional advice --- as this is what I do for a living, I don't sit all day in forum board --- I do have a life outside of HVAC, what little it is right now it's still a life...) You again trying to fit HVAC in a confined specific box in which it does not fit. What are the odds that someone will find that information useful? Probably close to 0% if I had to guess. That sounds like a waste of time... I know this seems productive to you so knock yourself out if you want to do that. Exact numbers are not necessary to educate everyone the source of the condensate. Then why not use the 'about 0.8 gallons estimate' and run with it? An air conditioner in my climate can produce upwards of 5 gallons of water an hour. A condensing furnace will not produce that much. An 80% non condensing furnace will produce 0 condensate water. Oh so let's use the AC condensate line for the furnace condensate. Problem solved right? Most likely not. Drain systems are complex especially when you throw in the variable that a condensing furnace imposes. See I've led your hand to this point --- where the concern right now up to this point is how much more condensate a condensing furnace will produce in my climate Katy, Texas versus other less humid climates in which those furnaces are installed typically in a basement. You don't have the over head flood threat you do here in my climate. All of this --- except: there are safeties on that condensing furnace that if you don't do it properly, the furnace will shut off on nuisance trips. So the furnace is not likely to be the cave in threat due to condensation production. They tend to leak water in drips around the furnace while having very erratic operation most often. You don't get these kinds of problems with a 80% non condensing furnace. What a home owner knows versus that of a pro... you think condensate is the only problem you have to contend with. What is your definition of making this actually work? How does the condensing furnace then become the ceiling cave in threat? Changes to the condensate drain system by people who don't know what they are doing. It may be a home owner, land lord or even a technician who doesn't understand the implications of what they are doing. How much water one produces whether here in this climate in Katy, Texas or a less humid climate (in winter) like Chicago / Wisconsin --- the different in condensate production doesn't matter... *IF* the system to get rid of condensate is adequate. This thread was about a young guy presumably in his 20's attempting to install a condensing furnace in a probable high humid climate. That condensing furnace was bought used. Who in their right mind sells a condensing furnace (used) in a probable high humid climate? One that tried to install said furnace and couldn't get it to work. I have an innate ability to read between the lines. I've seen quite a bit of 'Tom Foolery' in my nearly 26 years of doing this for a living. We can't get it to work so we'll take it out and sell it to someone else. So what makes the condensate drain system of a condensing furnace adequate? The right way. What is the right way? The opposite of wrong. If you want to learn how to do it: There are trade schools for that. Class dismissed......