Advice on high efficiency water heater for apartment buildings???

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Commercial appliances require commercial grade logistics. Verify the fuel supply to this device is per the manufacturer's spec. If the gas supply is insufficient, the combustion could be occurring at an improper mixture ratio and you could be producing CO byproducts in excess of the ventilation system's capability. Verify the passive ventilation system provided meets manufacturer's spec. Insufficient draft will not remove CO. This could be a consideration if someone gets a "deal" on a new heater and installs it without consideration of whether the existing vent system can handle it. It could also be indicative of a blockage in the vent. In a multiplex you could affect a lot of people simultaneously. 200kbtu sounds like you need a 3/4" gas line at .5 psi and perhaps larger if your heater is a long distance from the meter. If you are detecting CO, verify the above and investigate if the manufacturer offers an active vent option for the heater. I typically prefer passive systems but for this I want positive confirmation that the CO is being evacuated from the building.

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Yeah.. I am with @Steven Clark, get a few HVAC contractors to look at the issue and change the exhaust. Was this report from a home inspector or the city? Ask whomever did the inspection what should be done, Sounds like a power exhaust could be the answer.Ask them if this is urgent... this might be "just a thing they noticed".. ie.. no big deal or could be something they said needs to be done yesterday *however if that is the case, the city should have cut a permit to install this 3-4 years ago, if they did not go back to the seller to get this corrected, if they did this illegally (without telling the city)

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@Guy Azta I'm an architect not an HVAC engineer but I think atmospheric means it runs at a static vent pressure without a blower. There is typically a maximum horizontal run allowed before turning vertical or something to that effect. If it's too far from the sidewall you've got to go up unless there is an option from the mfr for a fan kit. Check with A.O. Smith for the options on that unit. The exhaust flue to the roof shouldn't be too expensive but may require being in a fire rated drywall shaft if it goes through multiple units on its way up. Once you confirm the requirements with the mfr a good local HVAC installer should be able to give you the best advice on a solution. Best of luck

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Hello @Kevin Guo - re-read your reply. Were you potentially saying that this heater is an overkill for a 12 unit building (it also has a small laundry site)? Again, I really know almost nothing about this subject matter. The last thing I want is having the tenants not having enough hot water, esp during winter. But it's good to know if in theory I could go with a smaller unit, since then it may make my original high efficiency idea make more sense.Should probably ask A.O. Smith what they think as well...

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Hi @Mark Fedorov @Steven Clark @Kevin Guo - thank you for the replies here. I'm new to BP, so still navigating the site. You guys are all correct pretty much. I actually spoke with the manufacturer A. O. Smith. They asked me to send them photos so that they can give me advice (which I haven't as of yet), but we already spoke about it in detail.So they have a new model which is the BTH - it has about 96% efficiency (mine is only 80%), and it would cost around $6-8K, not including installation. So I'm factoring around 15% utilities saving on a $3,500 annual G&E bill, and it comes down to about $500 at most. It will take more than 10 years for this to pay off. So in short: not worth it. BummerThe other 2 points:1. Why is it currently emitting carbon monoxide? Well, I haven't got deep into that since I was busy with all aspects of closing and pursing the deal. I'm going to get into it in more detail and be happy to share / get feedback. Here's what I got from the report: "Improper installation of the water heater exhaust system. The improper flue pipe material discharges out of a basement window. This is a safety concern due to improper combustion and carbon monoxide entering the structure. Suggest having the system properly exhausted for safety."2. What will be the remediation costs? According to A.O Smith, this unit is "atmospheric unit" (I love the big words) meaning it needs to be vented upward into the atmosphere and away from people. But it could potentially also be vented sideways, and I believe that's what they've done, but needs to be done properly (assumption). I'm still looking to getting costs and understand this better. I was told that we can relocate the heater to a better position and then get it vented through the chimney. But then I was told that I will have to maintain the chimney for the life of it. Again, I'm not well versed on these matters, so I may sound a bit like a bumbling idiot here. If there's a way to address this issue cheaply and safely, of course I want to do it.Now that I know it won't pay getting a new high efficiency heater, I'm going to find out what it takes to get this resolved, and share what I find here. Would love to get more feedback.Thanks!

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Looking at the description of the water heater you currently have it looks like a commercial unit. These are very expensive to install. If you're looking for a high end model you're probably looking at 10k+ (parts and labor). Commercial water heaters are built like a tank. A 12-unit apartment doesn't seem to be like a heavy load for it. You're looking at the water heater putting out almost 300 gallons in the first hour. So, you should be able to get a good life out of the current one.I'm guessing the problem with the carbon monoxide is that the exhaust fumes is getting pulled down? Probably whoever installed it didn't install a draft inducer/blower fan. What do the people you got estimates from propose on doing?

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I don't see value in replacing a 3-4 year old unit. I would get a 2nd estimate on the repairs also. If you want to get into the numbers yourself you can get a pretty quick life cycle cost analysis on the equipment options with this calculator from energy.gov https://energy.gov/eere/femp/energy-cost-calculator-electric-and-gas-water-heaters-0

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You need to compare the two... you should be able to look at that yellow sticker on the HWH to see the estimated cost per year... adjust that to your actual cost of gas and that is your answer....Actually you should ask the guy who wants to sell you the new one to do this...If you don't mind putting more detail... HOW is is emitting CO? without seeing it the problem is either the burner ($200-400) or the tin chimney (~$100) or the lack of air getting to the unit (cheep) ... I can't wrap my head around what would cost $2000.