For your home, a 28 kW should do with low flow fixtures since you don’t live in a cold winter area. I get quite a bit colder in the winter, so there’s a difference because the water is heated as it flows through and if it’s too cold at too high a flow rate, it won’t get as hot. If you want to play it safe or with higher flow fixtures, you might try the 32 kW, it will do a 40 degree rise at 5.5 gpm or 109 degree rise at 2 gpm. I recommend low flow fixtures, I have a fantastic Bricor .98 gpm shower head which I love. Remember, if you use more water, it takes more energy to heat it.

You can check out my experience at http://wiredforstereo.blogspot.com/2008/03/dont-get-water-heater-with-tank.html

Our home is a flat roof 1,100 sq. ft. single family residence facing north north. We require hot water for 2 full bathrooms, a kitchen w/dishwasher and a washer and drying.

Please advise where I can get more information (in layman terms) regarding purchase and installation costs, size needed, a comparison of the two systems and just what would be involved in replacing the current approx 40 gal. tank water heater.

I’ve perused the internet and am currently on technical information overload.

The first time, the flow switch stopped working after 1 week of use.

The second time, it stopped heating water after three months.

The third time, it still didn’t work right after I got it back.

After I got it back after the third time, it still doesn’t work. Now I have a 40 gallon tank water heater and I don’t have any problems.

The majority of efficency ratings I see on Tankless systems horn blow “No Loss” because they are eliminating the recirculation system and tank loss. Though this may be good selling point on efficency, it does nothing for comfort.

Scott, there is no balance between comfort and efficency. So for comfort, put the small tank infront of the “Tankless”. Set your circulator to just less than the flow switch GPM setpoint on the tankless and the temp for the tank type 10 degress less than the tankless delivery setpoint. This will not increase your overall efficency due to maintaining the circulation system, but you will be able to benifit from all the other aspects of a tankless system, longer life, endless hot water, generation efficency, elimination of sandwiches and wait times. Lastly, since it will be a new house, if you properly design your piping system, insulate properly, purchase a 92% plus gas instant heater you will have the best of both worlds. The most efficent system to deliver the comfort you want.

For the price you’ll be spending, there is virtually no benefit to your proposed system. Firstly, if you put the tankless before the tank, you’ll be heating the tank water needlessly before it gets heated by the tank. It would make much more sense to put the tankless after the tank so when the tank runs out, the tankless would kick in to finish the job. To do this, you’d need an electric tankless with the top off capability such as a SEISCO.

But finally, what’s the point of adding a tank anyway? No matter the tank’s efficiency, it’s still a fair shake less efficient than the tankless and that’s the prime reason for getting a tankless in the first place.

Your only benefit would be the power failure scenario, but only if you plan on taking a shower very soon after the power goes out as all tanks lose heat, and only if you take 1-2 minute showers with that size tank. Since it sounds like you have an electric setup, just go with an electric tankless of sufficient size and consider upgrading to low flow shower heads, the real kind like Bricor (can vouch, good stuff) not the 2.5 gpm nonsense that they sell in home improvement stores. I’ve had a SEISCO 28 kW unit for almost two years now and am very happy with it. It is coupled with a Bricor .98 gpm shower head and I can heat water from freezing to scalding forever.

Alternatively, a thermostatically controlled tankless could be installed downstream from the small tank and would only kick-in when the small tank ran out of hot water–or as a booster (keeping the smaller tank at a minimum temp, providing consistency for the input temp on the tankless and possibly allowing for a smaller tankless).

Has anyone tried any of these hybrid tank/tankless solutions? Am I killing the efficiencies for the sake of more consistent hot water?

Consider using a nuvoH2O water softener as I am and keeping your tank water heater. After reading these reviews, I am sticking with my tank–for now. But, my softener has crapped out after 9 years (Culligan) so I was looking at a non-salt replacement and thought why not reduce the size of the water heater, too. I still have to find some decent reviews for the nuco, though.