The Bosch Aquastar 250SX is the one I was thinking of getting, but your comment about the single lever faucets is something I did not consider. Would the problem be solved or alleviated by lowering the temp on the hot water to use proportionately more? What temp is yours set at?
Also, you said you used the existing flue for the exhaust. How did you keep it centered and what did you use to seal it off? Mine is 5" direct vent pipe, curretnly zero clearance to combustibles. I do not know what clearance would be appropriate for the 3" stainless inside there. I just ordered an infrared thermometer and will check the skin temp on the current outer flue. I would have to drill a hole in the outer pipe (then seal it) to get a reading off the inner. I believe the stainless is up around 450 degrees.
Beachwalker, the max. gas input for this heater(WH) is 175000btu/h which is to be used probably when 2 applications are in use. At the minimum the gas valve is calibrated for about 31000btu/h which is substantial, especially if you need only a little bit if water ( let's say 0.8 gpm, the minimum activation flow). During the summer when the input CW temperature is about 70F that 31k btu/h will simply overheat the water. As an example: I set mine at 100F (minimum temp allowed). I bought a digital thermometer and read the HW temp at the tap, at 0.8gpm flow. Well,...the readings were in between 125 and 135F!!. If I tried to mix-it with CW, the CW flow overcomed the .8 activation flow and turned off the WH. The result: me singing in the shower and instead of hot water: cold water (:( I've been in touch with the distributor of this WH and they recommended me to open another tap when I'm taking the shower!!! It's right, when the flow is enough, the 31k btuh will heat the HW to only 100F. But,..I don't see this as a solution. Probably, during the winter time, the CW temp will be lower and the HW temp will be lower aswell, providing more confort.
This summer we replaced the furnace and the WH. We bought the Rheem Mod, removed the old furnace 6" flue from the chimney and piped the mod through the side wall. Well, the old tank WH was this way orphaned into the chimney. When we decided to change and this one, we used the chimney's opening (about 8" square free area) to install the 3" SS z-vent.This depends of the height of the chimney, there are some limitations in the length of the run (26ft max, and subtract from this the equivalent pipe length for the elbows needed for the run). The Z-vent, you'll notice, is having self sealing silicon gaskets, and screw collers for installation. The max flue gases temp is about 430F for this WH.
Hope this will help you.
I've been running a Bosch 125hx for almost two years and have nothing but good things to say about it. Other than when the birds built a nest in my chimney liner, I haven't had any problems.
I personally have a Takagi. To be honest all gas fired tank less water heaters have the same concept. They all work the same. Some just have a higher capacity, and better warranties. Always remember the most expensive is not always the best, and remember when you go cheap, you get what you pay for… The best advice I can give all of you is contact manufactures. Find out all you can like sizing, capacity, and warranty. For you homeowners who are considering on going tank less take this piece of advice “Ask your installers for references”. Ask them who have they installed for, ask them for phone numbers. Contact these people and find out if they are satisfied. I do know that if the plumber/installer is reputable he will be more than happy to supply you with all the information.
I have had a Bosch 125B installed for over 4 years now. I would never go back to a tank type heater. Even with a 50 gallon gas heater, I was not able to fill the whirlpool tub in the winter months without running out of hot water. If I were building a new house, I would probably install two smaller units, one for the kitchen and laundry and one for the baths. Ideally situated to minimize the hot water pipe run. The unit I have only takes .5 gal/min to activate. Also, now when the kids come home for the holidays, everyone can get a hot shower without ever running out.
Knock on wood, my Bosch unit has also been very reliable and trouble free.
I was under the impression that the energy factor rating on water heaters already included standby losses... so that my throw off some of these payback calculations.
Also, I question the logic of using a tankless unit with a circulator pump instead of a tank style unit with no circulator. The advantage of the tankless unit is the higher energy factor that *results* from the lack of standby losses; adding the pump puts them back. You lose the heat from the pipes instead of from a tank.
I still like these units, don't get me wrong. As cool as they are, though- and I do still want one, if only for the nerd factor- the numbers still look to me like payback would be pretty slow in most retrofit applications... except maybe in a household that uses a really large amount of hot water. That's for gas, too.
Electric tank-style units already have energy factors of 0.92-0.94; even if a tankless electric has an energy factor of 1, a savings 6-7% on the energy consumption has a long way to go to cover the cost of the unit and all the extra wiring that has to go along with it. The one that I looked at took three 40A circuits, and drew 28 kilowatts under full load. I doubt many all-electric homes have an extra 120 amps of capacity in the main circuit panel or in the utility service line itself, and especially so during the winter heating season. The cost of upgrading to 300A service to make that work is enough that the payback will basically never come. If the space savings are attractive enough, though, go for it. It would be pretty cool to have a water heater the size of a good dictionary.
Don't forget that you'll probably buy two or three tank type water heaters during the service life of a tankless unit.
I didn't really get ours to save money, it's nice that our gas bill went down and all but it's the performance that I like. Endless hot water during a shower and no waiting for more hot water between showers. That's where the value is for me.
It's nice to have the extra floor space in the basement and you can also get hot water to cook with right out of the tap without worrying about sedement junk/dip tube fragments in your food.
When people are considering a tank less water heater with a circulating pump, there is still a lot of concern about the unit running constantly. Well when one installs a cirulating pump, it is always recommended that it is installed with an Aqua stat as well as a timer. Now with that being said, most tankless water heaters are flow activated. The pump will controll the flow, which means that when the pump is off the heater is off, when the pump is on the heater is on. An Aqua Stat, mounts to the return line and is wired into the pump. once the contacts on the stat close the pump will then energize thus pushing flow through the heater. Once the temperature is met on the on the return line the contacts then open and the pump shuts off. This in turn shuts the heater off. The Timer would act just like a a regular outlet timer. One would just set it for the times that the need for instantaneous hot water are greater. The last thing that one could do is just let the pump run countiuiously and let the heater cycle on and off. I do know that Takagi has built in thmperature sensors that measure the input temperature and the output temperature and cycle the heater on and off based upon the set point temperature. For example if you have your water set for 122 degrees, once the return line/input temperature reaches 122 the heater its self will shut down. The heater will not re-fire until the inlet temperature sensor reads roughly 10 degrees below set point. Now dont forget that this is with the pump running constantly. Note: having a pump run continuiously can cause dammage to your tankless water heater by errosion of the heat exchanger.
Takagi TK1s is 190,000 btu and are very nice,just make sure the debris scrren is mantained.