Always being one to willing experiment around, especially when it comes to a good friend. My friend Alfredo's 40 gallon water heater was out and he was getting tired of cold showers, so at first we tried to replace the thermo couple to his old heater, but it was of no avail, turns out the gas control valve was also kaput, along with some minor rust & leaks.
Plan B was to install new 40 gallon tank but then Alfredo decided if the cost was not that much different, then why not try out a tankless unit ? Now most folks know that it uses 50% less gas energy, but they don't know that the plumber has to rape you on the installation costs, because it requires more work the first time around. One hugh problem is that your old water heater uses a 1/2" gas line and the flex connector is only rated to 60,000 Btu - but your new heater requires up to 180,000 Btu. After you get home the plumber tells you he must install a new 3/4" gas line and at $600 to $1,200 depending on length to your gas meter your desire to turn green has you running to the bathroom overcome with the first wave of nausea.
Plan C since Alfredo is always willing to take a chance on my kookie advice. I suggested lets try getting the outdoor unit which is $300 cheaper then the indoor unit and let me make my special 4" dryer exhaust and I think we can have you in endless hot water ASAP. The only minor unknown problem being your 1/2" gas line, may only give you 3-4 GPM hot water, but if needed we could tap into your 3/4" gas line for the oven and go full power. So if you were still willing to only have 1 person at a time in the shower - my guess is NO PROBLEM. Oh and 2 more minor problems, I was not sure how the unit would work with the water softener & a recirculation pump.
Once installed, against all odds, against all codes & against all hope of working properly, we were actually very surprised at how well the thing cranks out the hot water. First we got lucky as the 1/2" line is only 25' from the meter - so it would easily pull 150,000 and did about 5-6 GPM of hot water.
The vent kit was very easy to make and slipped right into the old water heater vent. The recirculation pump appeared to work quite well also, so far so good. So now Alfredo has moved up to the 1% where he finally has endless hot water. Our installed cost was less then $1,000 and required about 8-10 hours labor including store shopping time, which is always considerable. Vs about $2,500+ if it was done 100% to code by a real licensed plumber with permits.
A small update below
you can see my patron insisted that we install
the required hot & cold safety valve set for $125
Look at the bottom left water heater corner
The front vent shows this is an exterior vent unit.
The top vent is interior unit , which requires extra $100 vent kit
this unit for some reason costs $300 more