we have had a lot of success with installing
tankless gas units on exterior of house.
then you don't have to purchase expensive venting
or cut into roof or wall to vent thru.
heat gain when unit is in use is to the ambinet
rather than the interior. (big plus in cooling climates)

I'm a fan of tankless gas units also!

I just filled my propane tank...$250 for 100 gallons.
down from last winter when it cost over $350 to fill.
While I do like tankless gas units...it would depend on
propane costs in your area.

water heater efficiency is Energy Factors. A standard
gas water heater's efficiency starts at .56
more efficient standard water heaters can achieve .65
by adding more insulation to the interior of the water heating unit...fatter water heater..more efficient.
(this is why externally insulating w/h's has a good payback)
tankless water heaters have energy factors of .80,
.82 and .85
.85 energy factor units qualify for federal tax credit.

Best of luck.

"Don't do it if your incoming water temps reach 80* in summer (Deep south or SW)."
Unless it's a Navien A model that doesn't care because of no minimum flow requirements or a bypass valve to cause problems with high inlet water temps

"we have had a lot of success with installing tankless gas units on exterior of house"
Only if you live in Florida, Texas, New Mexico or Louisiana, otherwise the first power outage with a freeze and your unit will be swiss cheese.

"tankless water heaters have energy factors of .80,.82 and .85"
They also have a .92. .95 and .97 Energy Factors too, if you look at better and more efficient models.

I installed a tankless hot water heater 4 years ago because my 10 year old tank water heater was showing signs of rusting out. Had one rust out in prior residence and 50 gallons of water flowed, luckily it was located in garage and all the water went out of the garage and down the driveway. Imagine if my 60 gallon tank located in the attic in our new house has rusted out and leaked the same way. Would not want to pay that repair bill!!!!

We liked the tankless system so much that we installed a larger unit in it's place (they will not provide the volume of hot water to run the number of applications as are advertised, a caveat here) and moved the smaller tankless to the other side of the house to replace a 40 gallon tank.

All is good now. Run dishwasher, clothes washer, kitchen sink and three bathroom sinks at the same time on the big tank and a single full bath on the small tank and never at a loss for hot water. Could not be happier with the convenience or cost factor.

Tankless is a great way to go!

Oh, installed it all myself, so it doesn't take a rocket scientist to install, you can do it yourself.

Hey ZL700,

Does the Navien have a bypass? That's good info to know. I hadn't run into the min flow issues until they were reported in the plumbing forum - I don't live where water inlet temps would ever get to 80*. You are about the condensing units having EF's in the .90's

Whether is is a tankless or a tank, two common plumbing codes that are followed in most areas require a drain pan under the unit.

Uniform Plumbing Code & International Residential Code both state:

Section RM2005.1 states that that water heaters should be installed in accordance
with manufacturerÂs installation instructions and the code requirements.
Section 2801.5 states that a drain pan and drain are required.

Section RM2005.1 General. Water heaters shall be installed in accordance with the manufacturer's installation instructions and the requirements of this code. Water heaters installed in an attic shall conform to the requirements of RM1305.1.3
.
RP2801.5 Required pan. Where water heaters or hot water storage tanks are installed in locations where leakage of the tanks or connections will cause damage, the tank or water heater shall be installed in a galvanized steel pan having a minimum thickness of 24 gage (0.016 inch) (0.4 mm) or other pans listed for such use."

Install is not as easy as it may sound, proper knowledge of gas piping and sizing, service capacity and appropriate venting must be understood and followed.

So many of the complainers of tankless, such as poster above that bought a undersized unit at first are the common causes of tankless complaints. In his case he bought a second unit, most would just complain and condemn tankless products. Also "professionals" often screw up the installs and applications also resulting in unwarranted slander of the tankless products.

"Does the Navien have a bypass? That's good info to know. I hadn't run into the min flow issues until they were reported in the plumbing forum - I don't live where water inlet temps would ever get to 80*. You are about the condensing units having EF's in the .90's"

Jake,
The Navien has no mixing bypass in the unit like the other flash units that superheat the water in the exchanger to 170-190 and then remix water downstream for temp control. That is why the copper heat exchangers with the intense heat are subject to liming. So they do have difficuties firing and staying on in minimum fire when the cold mix water is to high in temp.

The Navien has 100% flow through the #436 stainless steel heat exchangers. Since the unit's heat exchanger is capable of the flow, erosion and due to velocity, along with lower operating temps it is not susceptible to liming & calcification. The pitfall of the design is a slightly wider temp fluctuation than the Jap platform heaters, but this is not noticed so much in the "A" model that buffers that with the internal tank. IMO, the "A" model is the only way to go for the approx 125-150 cost upgrade.

The lack of mixing valve downstream, makes the Navien a perfect heater to add in-line to the output of a solar tank to raise the water temp only when tank is low or depleted due to usage or lack of solar input.

Rinnai has just released some info on their condensing water heater, 95%. Pitfalls are still polypropylene concentric venting and a Nicaloy primary heat exchanger which to me tells me both the install and unit cost will remain high. Only one left now without a unit above 90% is the Paloma/Rheem/Ruud line.

Good info ZL700.

I also agree with your post that a lot of installers/consumers don't know what they are doing and have given tankless an undeserved black eye.

On the other hand, there have been outrageous marketing claims and some bad equipment - such as the Bosch Aquastar -- that have caused a lot of problems too. Do you remember the Paloma/Rheem/Ruud 1-2-3 sizing guidelines? If you have a 1 bathroom house get model X, 2 bathroom get model Y, etc. Oversimplified it too much and didn't take into account gpm or inlet temps.

I think tankless are great - they need to get the installed cost down though. They also need to build competency in the installer base. We also need to stop designing homes where the water heater is in the garage and the master bath is 50'+ away.