Bosch AquaStar 125B Tankless Water Heaters... Meet High Demand North Americans
Written: Dec 18 '07 (Updated Dec 18 '07)
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Pros: Good for the environment, save energy, no standby losses, compact.
Cons: Often don't meet high water demands of North Americans, need maintenance plans factored in.
The Bottom Line: Under the right applications and with user education, these are efficient, environmentally friendly appliances. The buyer needs to research the product's true capabilities and their own needs to avoid disappointment.
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| the_gas_man's Full Review: Bosch AquaStar 125B NG Natural Gas Tankless Water ... |
Tankless, gas-fired, instantaneous water heaters have been trying to break into the North American markets since the late 1970's and early 1980's. It therefore isn't "new" technology, as countries like England, Germany, and Japan have all been manufacturing them for decades prior to the 1970's.
How It Works
This model is vented, usually through the same chimney as the old gas tank type water heater was vented through, or through gas approved B Vent to the roof. It also has an optional power vent system, for venting it through the outside wall or through a roof.
Once the gas and the water are connected to it, and the water supply pressure is at least 18 PSI (at 4 gallons a minute) by opening a tap to a sink, shower or tub, the water flow causes the gas valve to open and the gas is ignited by a standing pilot. The main burners are directly below a rectangular copper coated, finned tube heat exchanger which causes the water to follow a serpentine pattern above the flame, heating up before exiting the unit. If for any reason the outlet water gets excessively hot, a temperature sensor on that pipe opens and the gas valve shuts down. This prevents the water from flashing to steam or building up pressure. If the flue gases are not flowing up the chimney safely to the outside, another temperature switch is activated at around 270 degrees F and it too closes the gas valve.
These are the three most common causes of a service call for "no hot water", on a tankless heater, water pressure low, outlet temperature exceeded, chimney temperature exceeded and the pilot is now out too. These are all problems that your tank type water heater is not going to react to.
It Works For Other Countries, Why Not Here?
Tankless gas water heaters have been the accepted norm in most European and Far East countries for many years, mainly because they don't waste either water or fuel like North Americans do. They accept a few minor inconveniences, like additional servicing costs, lower flow rates and not being able to run multiple hot water appliances at the same time. (I.E. A shower, dishwasher and washing machine.) In fact, I doubt they even know that these things are considered inconveniences by North American standards, because they have never known any other ways, unless they have spent time over here. They often don't have basements to hide their water heaters in, so this unit would typically be prominently hung on the bathroom wall and another in a vented cupboard in the kitchen.
I have heard from those who have worked in Japan and Europe that their customers sign up for service contracts as a rule of thumb to have the heat exchangers cleaned annually. I can't imagine too many North Americans thinking that way. Call for service when it breaks, seems to be the rule of thumb here.
I've stood on the sidelines of the debates about tank versus tankless products for too long. I was actually first introduced to the Bosch product line in 1981. The company I worked for was asked to help have a few of their models approved for use in Canada. They were already approved for the U.S., but were having trouble getting sales off the ground and were looking for new market opportunities.
We (North Americans) want to save space, money on energy and conserve water, but we don't really want to give up any conveniences. Is it inconvenient to time your dishwasher to start at 10 PM? How about turning on the washing machine as you head out the door to work?
Number One Problem: Overselling The Product
The problems they encountered in the United States were directly related to overselling the capabilities of the product. You cannot call the model 125 a "whole house water heater" and it is not designed to "replace a 40 gallon tank type" water heater. I have seen these statements in advertisements for this model and others. All these companies are accomplishing is a growing angry mob of consumers who believed the hype, paid their money and are now demanding restitution.
One expert in this field has suggested we would need an instantaneous/tankless heater with an input rate of over 250,000 Btu's per hour to satisfy the hot water demands of the average North American family, or more than twice the input rate of the model 125B.
What Is The Difference?
In my house I have a 48 gallon U.S., (40 gal. Imperial) tank type water heater, that is set to keep the water in the tank on "stand by" at 120 degrees F, with a 40,000 Btu per hour burner and with a published recovery rate of 33.4 gallons per hour. In simple terms, it would take about 1.4 hours for my tank type water heater to raise a tank of cold water (50 degrees F incoming temp in the winter) to 120 degrees F. (This recovery rate will decrease over time with the accumulation of sediment in the bottom of the tank.)
However, I can run my tank type heater with two showers at a time, or a shower (at 3 gallons per minute diluted with cold water to about 95 F) a dishwasher and a washing machine ( at up to 140 degrees F) with no cold water dilution) and I am fairly assured of being able to have a long hot shower without fear of running out of hot water, while all of these other things are happening. Sorry to the person behind me, they are waiting about an hour for the tank to recover.
The Bosch 125B has a gas input rate of almost "three times" my tank unit at 117,000 Btu's per hour and is designed by Bosch as a point of use water heater. Ideal for a single shower or a dishwasher and then a washing machine, all operated sequentially, one after the other and not at the same time. If the operator accepts this limitation, they will have little to complain about.
This 117,000 Btu/H water heater is capable of raising the incoming water temperature of up to 3.6 gallons per minute by 50 degrees F. So at an incoming temperature of 50 F the outlet water temperature at the shower would be close to 100 F. More than sufficient for a nice hot shower, without using cold dilution. Higher water temperatures can be achieved by lowering the flow rate to 2 gallons per minute, the temperature of incoming water can be instantly raised by 90 F or 140 F at the outlet. You might use this mode for a dishwasher for sanitation purposes. However, don't forget that any water temperatures above 125 F can cause severe burns and scalds, which is why most tank type water heater manufacturers factory set the thermostat for about 120 F.
Location, Location, Location
I have heard complaints that these tankless units do not produce "instant" hot water. In many cases they are locating the water heater on the other end of the home, often where the old tank water heater was. Like a tank type heater, the water in the pipes will be cold, until the hot water pushes through, that does not change.
I had this model at my cottage and I located it on a wall just outside of the only bathroom in the building. It was ideal for a single shower (there was only one shower in the cottage) or for washing your hands in the basin. So, in my case, the water was instantaneously hot, as soon as I opened the tap I could hear the little burner on the other side of the wall swoosh into operation and the water would come through warm for a second or two, and then very hot. I suppose you have to take into account that I was pumping up lake water that would average about 60 to 65 F in the summer months and my pump pressure would fluctuate a bit towards the low minimum side. These units require a minimum water supply pressure of 18 PSI, so sometimes my pump had to build up to that, and the outflowing water would be hot enough to scald you, with a 50 to 90 degree temperature rise.
It was an ideal water heater for weekend use. I had a little 10 gallon electric tank water heater under the kitchen sink, which was adequate for doing dishes. Bearing in mind that I rarely used the cottage during the week, it was a weekend getaway place and barely accessible in winter. So admittedly, it saw limited use, but I didn't have to service it properly for five years and the gas costs were ridiculously low.
Long Term Operation And Avoiding Expensive Service
This heater has three flame settings and a mixing valve that you really need to play around with to achieve the ideal operating temperatures for your use. The ideal setting can depend in part on how far away the unit is located from the shower or sink, incoming water temperatures, flow rates and water pressures. For the sake of keeping the unit from overheating and it is better for it to run it at a lower firing rate with a higher flow rate. Operating it in this way keeps calcium from building up in the finned tube coil of the heat exchanger.
If you live in an area known to have hard water or high iron content, you should already have a water softener or an iron filter and it should be before this water heater to improve performance/life expectancy. Otherwise, you may have to have the heat exchanger periodically flushed out with a muriatic acidic solution. Failure to keep the coil clean may cause the main valve to close periodically do to fluctuating water pressures.
Still Want a Tankless Water Heater?
Why not? It only burns fuel when you "need hot water", it doesn't turn on and off 24/7 and 365 days a year, keeping a big tank of water ready for your whimsical demand. They are efficient, in the mid to high 80 % range, and many of them are approved for up to $300.00 rebates from the Department of Energy, which goes a long way towards the costs of the unit and the installation.
My recommendation for "whole house" conversion to tankless, is to look at the next model size up, sometimes referred to as the 250 and sometimes as the 2400. It has an input rate of 175,000 and can deliver up to 6.4 gallons per minute with a 45 degree F temperature rise and has a published operating efficiency of up to 87%. Just do me one favor, read all of the good and bad things noted above. Yes, it could save you money on your annual energy bill, especially with the rebate factored in. However, make yourself and your family aware of it's performance limitations and how you may have to sacrifice doing the dishes when you are showering or washing clothes.
In this case, size matters. If most of those who have complained about the lack of hot water on demand with the 125B, had only gone with the next size up, they would have been relatively happy. However, as I've said, it was perfect for my needs at the cottage.
Seriously consider a planned maintenance plan, particularly, if you went with the optional electronic ignition package, or the optional power vented package.
Finally, have your water tested and see if you live in a hard water region. These units are not good, performance wise, if there is a high calcium content in your local water. I also don't recommend these units for homes on wells.
If you have a cottage, this model is perfect in most cases. I've seen them used successfully in motels, condo's, public restrooms, office restrooms and places that only need a periodic supply of hot water to a single point.
If you can find a reputable dealer, who can get you the rebate and install the unit properly, for a reasonable price, you "should" be able to recover your premium capital costs, through your fuel savings over a tank type water heater within three to five years, depending on the volume of hot water your family consumes.
Due to the complexity of ensuring adequate gas and water supply, proper venting, and set up of the flow controls, this is a product I suggest you have professionally installed.
I hope this long-winded review has helped to shed some light on what can be a complicated little product, at only 29 3/4" high, 18 1/4" wide and 8 3/4" deep.
Be safe,
Regards,
The Gasman
Recommended:
Yes
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