For those of you interested in the bottom line on tankless water heaters, here it is. The complete story follows this list.
Advantages:- Installation is very expensive - probably as much as the unit. I recommend having someone local do it all, so you can get service when necessary.
- You can only heat so much water at once - usually 4-5 gpm depending on the temperature of the incoming water. This may be enough to run a shower and something else at the same time, but don't count on it.
- Electric units my require an upgrade to your electrical system (they take a lot of power). Natural gas units require large piping all the way to the unit.
- If you lose electricity, you lose hot water. Even the gas unit requires electricity to run the fan and controls.
- More moving parts means more things to go wrong (and fewer people around to work on them). It has certainly made me appreciate the simple tank water heaters.
My wife and I live in a 4-plex (all 1-bedroom units) that we own. We are fixing up & living in the bottom two while renting out the top two.
We bought it a little over a year ago, and the water heater was 25-30 years old (gotta love those Rheemglass Fury water heaters). It was also a 40-gallon water heater trying to serve 4 bathrooms while having the additional disadvantage of being seriously corroded by very hard water.
So we decided to take advantage of the tax credits that expired last year to put in a Takagi T-K3 tankless water heater - I figured we should spend about 1/2 as much on water heating, and have "endless" hot water. That is, we could take as many showers as we wanted back-to-back (not at the same time. The previous water heater lasted barely over one shower.
Of course, I searched on the internet for the best price I could find and bought one to install myself. Little did I know what I was getting into...
Installation Location
I had planned to install it in the same place the previous water heater had been - in the middle of the basement, venting into the chimney. After reading the manual (and talking to a plumber), I realized I could not vent it into the chimney unless I lined it or bought a special stainless steel vent to run all the way to the top. Considering this vent material cost about $20/foot, I quickly decided against that.
The plumber informed me that they are best installed on an exterior wall, with the special vent piping running straight up and out. Of course that would require about a 6" hole through the wood at the top of the basement wall. I did not really want to tackle that myself...
Installation Cost
I got a quote from the plumber to install it - $800-$900 including the vent materials. That's more than I paid for the heater!
I ended up spending almost $200 for the vent piping and $100-200 to cut the hole and install the sleeve through the wall. Add in some money for the additional 3/4" black gas piping we had to run, and there is probably $400 in materials. Plus my labor to install.
Definitely more work than I had planned on...
Operation
We had some immediate operational problems that took a long time to resolve. They ended up being my fault (mostly).
Do not install an "excess flow" or "safety" gas valve in the natural gas piping! These valves are designed to stop flow in the case of a hose breaking - when the flow rate gets too high. Guess what - at max burn on the water heater, the flowrate was too high, and the valve shut the gas off. Weeee! Cold water!
Once we resolved that, we dealt with really smelly exhaust (I could smell it on the other side of the house when the water heater was on). It ended up being an easy gas manifold pressure adjustment. Except for the fact that I had to buy an $85 digital manometer to make the adjustment.
After that, we had a continous fan noise. Tech support again walked me through what to do, and I found a piece of packing styrofoam in the fan. Not a huge deal, but annoying.
Most recently, we had a REALLY loud noise periodically (and eventually got an error code). Did I mention that the water heater stopped working late at night when I tenant was trying to shower? Again, weeee - cold water! Turned out this was because of dirty combustion (and incorrect manifold pressures). We still are not sure if it is because of the wrong pressures (and therefore bad combustion) or acidic condensate in the exhaust dripping back into the burner and heat exchanger. I guess we will find out...
Conclusions
Definitely know what you are getting into before switiching to a tankless water heater - I didn't.
If I were doing it all over again, I would get a unit from a local plumber and have him install it, or just get the 50-gallon tank water heater with the best insulation I could find.
It hasn't been bad to work on, but I like hands-on things. I also like now having the knowledge to fix a number of things on my own. At the same time, I like things to work the way they are supposed to.
I will keep you updated on any future issues with the unit. Otherwise, I am just looking forward to enjoying some natural gas savings!
