Bosch AquaStar Natural Gas Tankless Water Heater #250SX-NG

by Bosch

Product Description

From the Manufacturer

Cut water-heating costs by up to 50 percent with the Bosch AquaStar 250SX-NG tankless water heater. The 250SX-NG is fueled by natural gas and heats water on demand, supplying hot water at a rate of 6.4 gallons per minute--enough for two major outlets (shower, dishwasher, etc.) to be in use at the same time. When there is no demand for hot water, the unit’s gas valve automatically closes, and the burners turn off. A boon for basement-finishing plans, the unit takes up much less space than a tank heater and can be mounted in a closet or on a wall. The 250SX-NG features electronic ignition for automatic starts, computerized temperature control, and a built-in power vent for vertical venting. The AQ3 vent kit is required for horizontal venting. Not only does the 250SX-NG cut energy costs, but it also reduces greenhouse gas emissions up to 50 percent compared to tank-based water heaters. The purchase is covered by a manufacturer’s 12-year limited warranty. Check with your gas provider for energy rebates on this purchase.

Product Details

Choose the Right Water Heater [1.16mb PDF]

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Product Manual [2.73mb PDF]

• Product Dimensions: 8.5 x 15.8 x 23.5 inches
• Shipping Weight: 56.4 pounds
• Shipping: This item is also available for shipping to select countries outside the U.S.
• Shipping Advisory: This item must be shipped separately from other items in your order. Additional shipping charges will not apply.
• ASIN: B0006GVNZY
• Item model number: AQ250SX NG
• Average Customer Review: 2.4 out of 5 stars  See all reviews (18 customer reviews)
• Amazon Best Sellers Rank: #398,385 in Home Improvement (See Top 100 in Home Improvement)
• Discontinued by manufacturer: Yes

Customer Reviews

Most Helpful Customer Reviews

189 of 193 people found the following review helpful:

4.0 out of 5 stars Works for me, but not for everyone., April 7, 2006

By 

Roger Rammer "RJR" (Seattle, WA) - See all my reviews
(REAL NAME)   

This review is from: Bosch AquaStar Natural Gas Tankless Water Heater #250SX-NG (Tools & Home Improvement)

I have used the Internet extensively for information on tankless water heaters and this 250SX model in particular, so I wanted to fully detail my experiences accurately for others. In short, these things aren't for everyone, it depends on your usage and tolerance, your handyman ability, and the quality of plumbing in your home particularly water pressure. That being said, I am personally very happy with my 250SX set up, but I had to make some adjustments.

Usage: I only use hot water at the kitchen faucet, dishwasher, and clothes washer about once a week. I take a 10 or 15 minute shower every morning. About once a month I fill my 75 gallon jacuzzi. Rarely do I use hot water in the bathroom sinks for other uses, I often wash my hands in cold water. Other than the jacuzzi water and shower, I use very little hot water. Having a hot water tank of 75 gallons, or even 40 gallons, just does not make sense. The 250SX needs 0.8 gallon flow to activate the heating element. I take fairly hot showers and I keep the 250SX at 124 degrees. Because an extra 0.8 gallon flows through the pipes before the 250SX activates, some complain that it takes too long to get hot water, but I think it is no big deal. A bigger problem for some: when you turn off the hot water then turn it on again, your hot water that was in the pipe comes first, then the 0.8 cold water, then it gradually gets hot again. That is a little annoying. Imagine your wife turning the hot water on and off to wash dishes. A hot water tank would just keep the hot water flowing ready for on/off use, but not a tankless unit. It wasn't too big of a deal, but in the end I decided to solve the problem by adding a 6 gallon hot water tank (Ariston GL6+) in series after the 250SX. The 250SX has 3/4 inch NPT water threads, to keep the pressure constant make sure you get a small holding tank that also has 3/4 inch NPT water threads. The hot water always flows through the hot water tank last and the outward source recieves hot water from the small holding tank first. Also, the 0.8 gallon of cold water flows into the small tank first where it is mixed with 6 gallons tanked hot water. Set the small tank at about 4 degrees higher than the 250SX and you won't even know the difference in temperature; problem solved. One guy told me that his wife insists that the hot water must be 140 degrees in the dishwasher, but she also likes luke-warm showers. The problem here is that the 250SX does not get the 0.8 gallon of flow when she is in the shower. Add the fact that she messes with the shower's water controls and the unit goes from on (hot) to off (cold) while she is in the shower. Apparently, that really pisses her off. The small holding tank helps with this too, but there are several ways to solve this problem: 1) get a new wife, 2) use Bosch's remote temperature control (about $120 extra) at the shower to turn down the temperature, 3) turn on a bathroom faucet while she showers (wasting a lot of hot water) 4) my new dishwasher (this recently went out too) has an option to superheat the water it uses (it must have a separate water heater). Some people complain that the unit causes less hot water pressure, but that is not my experience at all. It helps to have good water pressure to begin with (mine is 70 psi) but maybe the hard piping to keep 3/4 of water flowing without bottlenecks helps too. Some people complain that the unit makes a high pitched noise, but that is not my experience either. I will say this: for a short time I had it connected to the previous tanks 1/2 inch gas line. It did make this noise a little when two hot water appliances worked at the same time; probably has to do with needing more gas than available in the 1/2 inch line. In that case, that problem is solved by hard piping a 3/4 inch gas pipe to the 250SX. It seems to me all these problems are related to particular usage or to improper installation; READ THE INSTALLATION MANUAL.

Installation: The venting exhaust must be on its own line, NOT combined with say your furnace exhaust. Also, be sure you incline the exhaut pipe upward if venting horizontally as the manufacturer requires. Incidentally, the model's installation instructions are available on the Internet, READ THE INSTALLATION MANUAL. The 250SX drinks in 175,000 BTU when it is working hard, that might mean you will need to upgrade your gas line. In my case, I was replacing my furnace as well as the water heater. The guy that installed the furnace, used the previous 3/4 inch gas line for the 250 SX, then ran another gas line for the new furnace. Since it was part of the bid, I have no way of knowing the cost, but I would guess the cost at $75 of the furnace bid. To insure that the 250SX gets sufficient gas, the installation manual strongly suggests that the gas line be hard piped to the unit which is what the furnace guy did for me. Another guy told me to hard pipe the water lines to unsure that there are no bottle necks in the water pressure. Apparently, a 3/4 inch flex line is actually 5/8 inch in the middle. I sweated the 3/4 inch copper pipe from the cold water source to the 250SX, then to the 6 gallon holding tank, then to the hot water line; all water runs through 3/4 inch copper pipe with unions for quick uninstall if either the 250SX or the holding tank needs to be replaced someday. You will need an outlet for the 250SX pilotless ignition, but I think it takes very little power. If you install the Ariston tank, it requires a 20 amp circuit hardwired to the unit. So, you've got to know a little about electrical, plumbing for copper pipe, and basic handyman skills for everything else. I found it to be a fun little installation project. You can also contract out the installation but it is rather expensive.

Costs: I bought mine at a local hardware store for $899 + tax. The expenses don't stop there, if properly installed this model MUST HAVE a special sealed 3 inch stainless steel pipe for hot gas (carbon monoxide) exhaust, plus a wall thimble and a termination hood. I needed 13.5 feet of exhaust venting (AL29 type) which I bought on the Internet (Cinnabar) for $292. The optional small holding tank (Ariston GL6+) cost me $174 (from Ace hardware on the Internet, have them send it to one of their stores). There is another $150 to $200 in other materials, including a 20 amp circuit plus 12 gauge wire for the small holding tank which needs to be hard wired, copper pipe, etc. The 250SX itself needs an outlet for pilotless ignition. You are supposed to have both on separate curcuits, but I felt this was not necessary, so I put them on the same circuit, outlet and hardwire to the small tank. In total, everything cost me about $1650 with the small tank and installing everything myself. Figure more if you need to increase your gas line as these things suck 175,000 BTUs when loaded, plus $800 to $1500 more if you have someone else install it for you. I got a quote for about $800 for the install not including the small holding tank or the extra for the increased gas line.

Analysis: I figure a quality large water heater, big enough for my Jacuzzi, would be about $800 installed. I will get $300 back in a Federal Tax credit, so the tankless unit setup is $550 in extra expenses that have to be made up in savings ($1650 - $800 -$300 = $550). I figure I save $8 a month in energy costs when I subtract the $2.50 a month to operate the small 6 gallon water tank. It depends on how much hot water you use, others claim they save $20 a month. That means it will take me about 6 years to break even. The warranty is 12 years on the 250SX and 6 years on the GL+6. Keep in mind that tankless units are expected to give twice the service of a water tank. That make sense since most water tanks rust out trying to hold all that water. I have used the 250SX for 2 months now. I'm tickled pink by the unit, but NOT because of my marginal energy savings. With the small tank in series, it acts a lot like the tank I replaced, except the hot water is endless, great for the Jacuzzi, and a lot of room is freed up in my garage. Bottom line: If you 1) have good water pressure (a must), 2) are able to install it yourself, 3) have other reasons besides energy savings to install, then I highly recommend it. If you are lacking on these 3 points then do yourself a favor and just replace your old hot water tank with another.

65 of 68 people found the following review helpful:

4.0 out of 5 stars Bosch Tankless Whole House Water Heater 250SX, December 20, 2005

By 

Paul (Davis Ca) - See all my reviews

This review is from: Bosch AquaStar Natural Gas Tankless Water Heater #250SX-NG (Tools & Home Improvement)

Tankless water heaters are the wave of the future if you ask me. They're using them all over western europe already, because they can't afford to waste energy. We can't in the US either, but then we're encouraged to. Over the life of the water heater, you'll save a lot of money on your tankless water heater.

Tankless water heaters are DIFFERENT than the one you're used to. So you have to shift your expectations. The difference? Tankless water heaters don't STORE hot water, they make it as you use it. Therefore, if they can't make enough, they run cold(er). If they can make enough (like when you take a shower) they'll never run out. Their problems are different too. Their sensing circuitry is more high tech, and computer controlled. When gas pressure or water pressure fluxuates, so can the temperature. It takes very little handle adjustment to make a big change in temperature. You might also consider buying the remote temperature controller. I can see where that might make your life a bit easier when switching from the shower to the tub.

Now to the 250SX. We've been running ours in San Francisco for about 5 months. We put it in the attic to get it out of the living space. Its gas fired. It supplies a tub and a shower simultaneously (and actually works a bit better when you turn on both than it does when you use only 1). Gas and water pressure fluxuations affect the temperature of a shower, which can take some adjustment. The power bills are down as a result .. no wasted water heating when you're not using it. Turning on other appliances can affect the temperature and actually make the water run cold, depending on how much pressure you have in your house and how much it fluctuates naturally. There seems to be a good case for installing pressure regulation to use this applicance, though we didn't. We're currently considering installing a second unit just for the dishwasher and sink.

Its a nice, quiet, efficient unit. Its easy to understand. It takes some reading to install it correctly (your building department will help you do that, but you have to work with them). The space savings are great. There's a computer involved, so you have to read and understand the error codes so you can troubleshoot it if it has problems. I reccomend getting a plumber with experienced to help you plan the installation, and size the unit. It gets more technical than just about any other household installation.

That said .. might as well ride the wave of the future now, save yourself some money, the planet some hydrocarbons, and some of that valuable real estate you paid so much for.

43 of 50 people found the following review helpful:

3.0 out of 5 stars Not a general purpose retrofit - good for new construction or tech geeks, January 15, 2007

By 

infrequent buyer (mountain view, CA USA) - See all my reviews

This review is from: Bosch AquaStar Natural Gas Tankless Water Heater #250SX-NG (Tools & Home Improvement)

Before you hear my rant, I think these would probably be great for new construction where your house is under warrenty. I think energy efficent and green products are really worth the premium and extra effort, but this technology was such an big let down for me. Because of my faith in Green, I'm giving it a 3.

Be aware most retrofits require a relocation of your heater. (ie reroute water, gas, vents) Also be forewarned these are computers and you will have no hot water during a power outage. In addition, while the installation is a bit easier than tank water heaters, be prepared for technical issues. Instant heaters in general are a very complicated solution to a very simple problem (ie. make the water hot).

My old water heater tank started leaking so I thought it would be a good idea to try something less prone to corrosion and leakage. After doing some investigation, looking past what the naysayers claimed, I purchased the Bosch AquaStar 250 SX from Lowes. It seemed I was very fortunate, since most tankless water heater "retrofits" require a massive, expensive replumbing effort, yet mine did not require a relocation. (As a comparision, a cheap water heater can be installed for under $500.)

Pro's: Installation is FAR simplier than a water heater, mostly because the unit is compact and there's no crawling needed to install the pipes. It looks fancy, it has a LCD panel with buttons on it, and it takes up a lot less closet/garage space.

Con's: Works for 2 things, so no more kicking off the disher and washing machine, and hitting the showers once you put the kids to sleep. Relies on electricty, so no hot water if you have an blackout or "dirty" power. Requires more a controlled environment to operate. Many moving parts, wires and a full blown computer inches under a tank of scalding hot water. Requires more expensive plumbers as there is relatively US expertise right now.

It is way way OVER-ENGINEERED for what it does. You won't believe how many wires, electrcal components and moving parts this thing has. "Fire on water makes water hot", right? Not so simple. Unlike a tank with a fire under it, be aware YOU ARE INSTALLING A COMPUTER attached to motors and sensors, with water running through it. As such, you must accept all the downsides of owning a computer running under relatively "extreme" conditions.

I'm sure it works fine most of the time, but now in addition to metal corrosion, you have to worry about one MORE major component that will fail. As a comparision, my house furnace failed twice, both times due to a bad "control system". When things fail with this Bosch AquaStar 250SX, you have to read highly generalized computer error codes, and report them to a computer technician at Bosch. When I called Bosch, I felt like I was calling computer support. Ultimately, they debugged the system to a point where I had to either pay a contractor to come in and measure the gas pressure or buy my own diagnotic tool (a manometer - ie yet another computer). Even though the gas, water and exhaust are replumbed/retrofit well enough for a conventional water heater, the fire will only light if the computer's internal diagnostics decide its ok to do so. In short, you will hook up everything far better than you would with a tank and you still won't have hot water.

I spent about 13 hours getting the pipes replumbed, added the extra shutoff valves and addressed all the special requirements like stainless steel vent pipes, etc). This part was rather easy. I was happy to see Bosch had exacting standards. Best part was there was no crawling or upside-down soldering. However, never underestimate a computer's to make a simple problem extemely complex.

No matter what I tried, no matter how much I heated up the room, no matter how often I flushed the gas and water lines, I kept getting cascading error codes from the computer. Ultimately it ended up with some "ionization electrode" error which appears to be a catch-all meaning "the computer notices your fire is not lit". In addition, the unit kept leaking water from the top level to the bottom level. I'm not sure if this was condensation or a leak of some sort.

New technology, not old technology refined. Do not believe the hype about these being a mature peice of technology. I have seen flash heaters in Asia and Europe and they are radically differnt. Overseas, they are reliable low tech, point of delivery devices. When a person wants water, he pushes a button and instant hot water. With an American "instant heat" tankless water heater, you rely on a computer to allow the water to flow and the gas to burn. There's no override or way to jump it like in a furnace. I can't wait for the first brownout or period of "dirty" power to fry a neighborhood of these computers.

So, if you're really going to spend $999 + $200 in special parts to do this yourself, consider some more reliable, enviroment friendly solutions. Solar panels are a more mature technology, warm the water on cloudly days, have $0 monthly cost of ownership, and have 0 carbon emissions. If you stand foreign products (like this Bosch) I suggest you investigate some of the Chinese compact, efficient roof mounted water tanks.

My advice, build a new house with one, wait a decade until the kinks are shaken out and try it on your retrofit, or stick with an efficient tank.