Atmor Instant Tankless Electric Water Heaters

Comments/Discussion from a previous sale

Time to learn all about Atmor

Hey Woot!

The 13 kw unit with a 60 amp circuit breaker requires a #6 conductor, not a # 8 as shown in the chart. You can however use #8 on the 8.5 kw unit with a 40 amp circuit breaker.

I can’t comment on this particular item…but I can provide some feedback on tankless water heaters in general as I just installed one in my house.

Big house, 3500ish s.f. I had two 50 gallon natural gas hot water tanks that were past their prime. Decided to rip them both out and install a natural gas Takagi condensing 10gpm tankless. 95-96% efficient so there’s barely any exhaust…but did require some venting work.

I’m in Chicago and I did this in the middle of winter. Incoming water was ~50 degrees and takagi was set to 120 degrees at first, and then raised to 140.

The tankless worked great from the get go but given the cold temperature of the incoming water, and the distance the hot water had to travel given the size of the house, it was taking upwards of 5 minutes for the hot water to reach some of the faucets.

I already had a gravity fed recirculation loop for the old tanks. Of course that wouldn’t work with the tankless because it needs .5gpm flow rate to kick on which the recirc return could not provide. Even it did, that would mean the tankless would be on constantly which would be wasteful and worse than having the tanks.

I could have installed a recirc pump but given the erratic usage patterns, timer based recirculation didn’t make sense and would also waste both gas and electricity.

So, I decided to get a 6gallon Bosch electric tank. I put this tank after the tankless and tied the recirc return into it so the recirculation loop is working again water is always hot in the pipes…and of course when a faucet generates flow, the tankless kicks on because otherwise the 6 gallon tank would have no hope of keeping up with demand.

Works perfectly. Now I just need to find out how much power the Bosch is using…plugged it into a Kill-A-Watt so we shall see soon enough.

Wow! 13kW of torque! That’s a lot of torque for a tankless water heater. Reeeeaaaalllyyyy torque-y.


Flow rates defined: if your water was flowing at a rate of 2.15 gallons per minute (GPM), the AT-900-10 unit can raise the temperature of the water by 35 degrees fahrenheit. For example, if the average cold water temperature in Miami is 77 fahrenheit degrees, the water temperature in the outlet will be 77+35= 112 fahrenheit degrees. The average water heater is set at 110 degrees fahrenheit.

BTW: Shouldn’t rinse be raise or rise?

I bought the 13kw-240 model the during the last sale. I use it in my greenhouse to raise the water temperature out there. It serves my needs well, as long as I don’t turn the water on full blast. It would work great for hand washing, or if you have lower water pressure. I can’t imagine if would get the water hot enough if using it for a shower.

I have been using a similar electric tankless system for the last 15 years. I will try to help explain what to expect.

  1. Your lights will noticeably dim any time there is a call for hot water.
  2. It is just idiotic to set a tankless heater at anything over 104 degrees. Set the temp at the hottest shower person. Why would you spend all that money heating water and then just cool it down.
  3. Consider getting 2 of them in series to assure you have the capacity you need. As a side benefit, you have a backup during repairs. Plumb accordingly.
  4. You MUST, and I do mean MUST, install a good filter just prior to the inlet. If not, you can expect a failure fairly shortly.

With all that said, I would NEVER go back. Besides cleaning up and condensing the space, having continuous hot water when I had 2 teenage girls at home would have been just maddening. If you use a generator, consider getting the smallest one as the 2nd in series. You can shut off the main unit and still have at least a trickle of hot water. I have 2 larger units in parallel, and a small third after that. I have shutoffs positioned so I can switch between the parallel units.(I only use one at a time) I can quickly take one out of service with no interruptions during repairs.

Do you mean the average tankless or the average tank water heater? If the latter, I believe they are normally set to 130, not 110. I can believe an under-the-sink in-line heater might be set to 110, but I know my basement tank heater was set by the plumber to 130. He was not legally allowed to set it higher but I adjusted it myself to 135 as I found the water at the faucets to be a smidge low.

All that said, I would not know what a tankless would usually be set to. I guess it would be dependent on where it was located? If it was as far away as a tank, wouldn’t it need to be set the same as a tank, as both would need to allow for heat loss between the heater and the faucet?

I’m not finding these models on the Atmor website. Does that mean they are older, out-dated models?

Rinnai commercial tankless units are almost bulletproof. You get what you pay for. Best ever upgrade to my home. Gas is also the better option compared to electric. My two cents?-pass on this mickey mouse unit. Expect to spend 1500.00-2000.00 to get the job done right.

Not sure what the above means, but we just moved into a place with a tankless (not this brand, Ecosmart) and if I put the temperature at anything less than the max of 140, I have to run my kitchen faucet (which is about 4 feet away from the tankless) at less than 50% or I will get tepid water.

The bathroom is about 18-20 feet from the kitchen (550sq ft unit) and running the bathtub results in freezing water due to the flow I guess. The shower has to have the handle turned all the way to the left at the max hot and it’s hot but nowhere near anything you’d think was too hot. The scald control is set to max hot.

It’s been a freezing winter here in the northeast so that may account for it but I recall when we moved in last July that putting the shower on max hot water with the heater set at 110 was laughable and had to cranked to 140 at that time. I’ll see what happens when the weather changes.

I would much rather have the tankless, but you have to be really sure what size you need before having it installed. I looked at the Ecosmart web site and the next model up from the one I have requires 3 wires to the electrical box and the one I have requires two. While I’m not sure exactly what that means, it sounds like it would be expensive to have this box removed and a new, larger capacity box installed.

DO NOT use a tankless unless you have soft water.

Recommend a high quality German made 2 or 6 gallon Steibel Eltron tank installed at the point of use. It’s only 120V. Plug it in with attached cable. I have the 2 gallon under the kitchen sink and love it. I run water from a 50 gal. water heater into the “cool” input, hot output to the sink. Instant hot water!

Just so no one is confused. These would be considered ‘Point of Use’ water heaters. That is, they are installed at the point of use. Say, under the kitchen sink to provide hot water at that sink or for the sink and dish washer. I installed a similar Bosch unit at the kitchen sink because it was so far from the main tank heater. 4 gal of water to get hot. Having instant water at the sink was great. I was fortunate to have 220v close by because I had replaced an electric cooktop with gas. Otherwise the wiring would have made this out of economic reason.
So, my units lasted an avg of 4 years. Third unit is still working but… Maybe the Atmor is better. Don’t know.
My main point is these are not designed to be a house system. Look at their website.
The illustrations show point of use pics. Otherwise you are doing what Marklwood did. Three in series to get hot enough water.

Did my homework - compared to Bosch Steibel is the best built and of higher quality. 120V makes it a no brainer. Wife now has instant hot water at the sink rather than wasting hot water that is stuck in the line just as she turns off the hot water side of the kitchen faucet.

we have an outdoor kitchen with cold only water. It’s fine for cooking but I can’t do dishes out there, and have to lug them into the house. This would be ideal. Being in Vancouver, BC we never get it very cold so our water should warm up nicely with one of these

The pop off valve on a water heater is at 140. The plumber was wrong. Scalding can occur in seconds at 130. That is why they are never set above 120. And then only if there are no children or elderly/disabled.

The point was that you have to think differently. When you have a tank, you are limited by the size of the tank. That is why the need for the hotter water. When you go tankless, it is pointless and wasteful to heat water past the temperature of use. You will not run out. Ours is currently set at 101 because that is where I like my shower. My wife mixes just a touch of cold.

A 110v unit is just undersized. You could never get enough KWs to heat water for a good shower. You would have to use a shower head rated at 0.5 gallons a minute and pray no one turned on a faucet while you were in there. It sounds like the kitchen faucet is either older, or had the water saver bypassed, making the flow rate too high for the unit. You are right about the incoming temp of the water. The KWs of the unit determine the RISE in temp of the water. The warmer the water, the less energy needed to heat it.

I wouldn’t use one of these where you could possibly get freezing temps. The heating chamber looks to be made of plastic that would easily bust. If you did use it outside, have a way to drain and blow out the water if you think it is going to get close to freezing.