zl700 I'm really wondering which brands/models you have experience with that are so noisy? Where does that noise you are describing originate? Are they vented through a flue straight up through the home or are they direct vent through a wall? We were thinking of adding a second tankless for a master bath expansion, but if the new ones you've experienced are so noisy, I don't think I want one located close to where I sleep. I've lived with a tankless for going on 14 years now, and have never had anywhere near the level of sound that you are describing. Mine is in my laundry room about 5 feet away from the washer and when I do a hot water only wash, the washer filling makes more noise than the water heater does. As I said, you can hear a soft "whoomp" as the burners light, and a bit of water flow noise through the pipes, but it's barely audible standing at the washer 5 feet away. There is no gas pipe noise. I've never even heard gas piping make any real noise and we've got gas heat and stove. In fact, my gas fired forced air heater in the attic makes more noise when the burners light than the water heater does---not counting the sound of the air through the ducts. My water heater is a Myson, which I don't know if it's still made as it's an old fashioned design without fancy computerized controls. But it's worked very well for almost 14 years now--and with very little noise. :) I'll probably do a search and see if I can find another one if all of the newer brands aren't as quiet.

Ionized: FYI: I put those formulas into an Excel spreadsheet so that they were more plug-n-chug. The original estimate for payback on my gas tankless was 5 years vs a standard 40 gal tank heater.(~a $500 difference in installed price - DIY) The revised payback with lower gas prices is 8 years. That's okay, but not great - but that's compared to a standard gas tank. I couldn't use a standard gas tank without re-lining my chimney or using a powervent. The powervent was the same cost as the tankless - so it's all savings for me. All that said, I live in central Indiana where it can get downright cold. Everything in my 100 year old house is gas incl. furnace, water heater, range and dryer. My average gas bill (budget) is $46 - and that's before the mild winter this year and the foam insulation I added on the basement walls and joist pockets. My winter electric bill is $35. I keep things at 68-70 degrees inside. The continuous hot water is very nice, not having a big tank is great, but not having anxiety attacks over utility bills is wonderful. Of course it's not just the water heater, it's the 92% furnace and insulation and such... I still have the original windows though. Even with the reduced cost of natural gas, if someone can install a tankless at a reasonable cost (no re-doing the gas service) I would advise that people consider it. In hot climates, the heat pump water heater sounds like a great option - esp in electric only situations.

My last water heater lasted 16 years. Personally, before I spent a bunch of money on a new heater, I would try a quick cleaning. It is actually MUCH easier than that article makes it seem. It is the same way you would clean a coffee pot, but on a much larger scale. Dump out the junk, rinse it clean, hit it with a cleaner, and rinse again. Basically, you just turn off the water heater, shut off the water, turn any faucet in the house to hot, and then drain the tank out the bottom. The water coming out will likely be a gunky mess. If so, close the drain up, turn the water back on for a minute, turn the water off, and drain it again. Repeat as long as you are getting gunk out instead of clean water. Pour in some vinegar, let it sit for a few minutes. Add some water, drain. Add some water, drain. Fill it back up with water and turn the heat back on. Depending on how bad the problem is, you may be able to fix it for $5 of vinegar and a couple hours time.

@nwfan, did you ever solve the issue with your machine? We have a 2010 Miele Inspira that has also been making a similar noise for some time--we replaced the impeller for the circulation pump a few months ago (fortunately Miele USA does still sell the parts separately, though you have to call them directly) after finding that the impeller had split into two just like Petr's photo, which improved but did not entirely resolve the noise. Ignored it after that since it was cleaning fine but now it is giving us an F14 fault code and stopping at that point in the cycle, so clearly the noise was indicating something wrong. We've taken it all apart and checked most everything that is a common source of that code but nothing seems obviously amiss, so we're running out of ideas. Curious to know whether you found a solution (and if so, what the problem ultimately was).