Atmor Tankless Water Heaters

That will work just fine, the electric unit will automatically switch off once the water entering it is a higher temp than the set point. If you pay for water (metered connection) then your water usage will decrease because the cold water down the drain while waiting for it to heat up will be eliminated. You will also save that time waiting for hot water. These units are most effective the closer they are placed to the point of use.

"So… due to the flow rate this may not even be good for a shower?

No way. Well, a Navy shower maybe"

Well crap! I just ordered 3 of the big ones. The chart shows it is the size for a sink and shower. What the heck!

What are my options now? Could I possibly hook it up to my current Hot water line and turn my water heater tank to lowest temp? Any savings in that? Or should I just attempt to return them?

Most tankless heaters have a max water inlet temperature that’s less than supplied by the existing hot water supply line. Besides, why waste the main tank’s hot water when you’ll have all that you need in a few seconds of turning on the tap?

As philgonet mentions, it depends on what your situation is.

What state are you located in? (roughly tells water line incoming temperature during winter)

What hot water temperature are you aiming for? (this minus previous = desired temperature rise)

Did you measure the gpm of your showerhead? (take a 1 gallon bucket, turn on the shower, stuff bucket under and start timer, stop timer when bucket fills, calculate flow rate)

These sort of have a fixed rise based on their max output, so a person in, say, Texas might be served well with the larger unit, while a person in north Minnesota would wonder he ever bought one.

btw, why did you order 3?


Most electric tankless I’ve used or read about are not vented to the outside. You’re probably thinking a gas or propane tankless water heater, like a Takagi.

Your installation costs are pretty off too, but it depends on the unit you are sizing.

Electric only? Why can’t Woot offer a natural gas option? I know somebody makes that option.

[QUOTE=mrln, post:24, topic:428977]

“What state are you located in?”

GA. I went one up from what the chart recommends. First I figure they fudge on what you really need. Second, while AVR temps are pretty high, the temp can be pretty low after a cold snap.

What hot water temperature are you aiming for?

Never measured my showering water temp and assume the dishwasher heat function will raise temp to what is needed. I’ve never seen the need to have scalding water at a sink.

I keep my water heater set at 120 so I guess my temp needs are lower than others might be. Also this saves me some money and grandkids never get ‘burned’ washing their hands.

Did you measure the gpm of your showerhead?

No, but stated is 2.5 gpm as are most units sold now.

btw, why did you order 3?

Moving to another house with two bathrooms and kitchen with adjacent laundry room, all some distance from water heater now. I like the idea of having quick hot water at sinks rather than having to wait and wait plas hate the idea of wasting all that heated water in the lines between the using area and the water heater.I will probably have to install new breaker box anyway (older house) so decided it would be a good time to go to tankless and try to save some money, by turning current water heater off and using them.

Tankless water heaters save space, not energy. That is the value.

“For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24%–34% more energy efficient than conventional storage tank water heaters. They can be 8%–14% more energy efficient for homes that use a lot of hot water – around 86 gallons per day. You can achieve even greater energy savings of 27%–50% if you install a demand water heater at each hot water outlet. ENERGY STAR® estimates that a typical family can save $100 or more per year”

I tend to use the (another mfg) site. They also seem more conservative in their estimates too.

They say north Georgia low is 62, south 67. I’ll just use 65deg.

You ordered the 13kw ones? 13kw using the ecosmart equations:

At 120deg from 65 degrees (55deg rise) at 2.5 gal/min, you need a 20amp model.

For a 55deg rise, a 13kw model can handle a flow rate of 1.6gal/min.

For 2.5gal/min, a 13kw model can handle a 35deg rise, so 90deg.

All in all, the 13kw seems undersized a bit. You could put 2 inline to one another but you’d have to set one of the units to a lower setting (if not, likely would trip a temperature safety on the downstream unit); I wouldn’t recommend the hassle of doing that.

What’s your main/service amperage? 55amps on 60amp breakers, if you have all 3 running on 200amp service it’ll trip the main. (I’m not convinced these here are modulating so I think they come full electrically when triggered.) If it’s an older home, a lot are still on 100 amp service.

If your main can handle it, your geographic location seems good for tankless.

I’m not quite sure I have a handle on the home layout though.

If you can find a central location plumbing-wise, I would have gone with a Ecosmart 27 (3.1gal/min) or a Stiebel Eltron Tempra 29 Plus (pricey). Amazon had a Gold Box on the Ecosmart a short while ago for $360, but it’s also come up 2-3x in the past year on their Lightning deals for around $370-390. These are also modulating units.

I’ve cut most of your reply out. Thanks for the input. Many things to think about.

We (condo board) have considered adding a hot water recirculating system to the condo as a whole but it is not worth the cost. (Condo is a three story U-shaped building, with boiler in basement at bottom right of bend and 16 apartments of varying sizes.)

My breaker panel is currently full but I can easily swap in narrow breakers to get what I need. Wiring to the 1st floor bathroom is easy (~7’), though it would probably make more sense to put the tankless heater in the basement bathroom near the ceiling (~5’ of wiring) so as to pipe in both bathrooms.

I think you are correct about the flow switching, so these units are probably not right for my idea. Also, the manual says to only connect to cold water.

Thanks for names of manufacturers of other units. Will look at them.

Hmmm… We (condo board) supposedly looked into this and I was told (by another board member, who did the research) that cost would be more like $5k. Perhaps I should look into this again myself. Thanks.

[QUOTE=mrln, post:29, topic:428977]

“All in all, the 13kw seems undersized a bit.”

It’s the largest one Woot offered.

“You could put 2 inline to one another”

Buy six then. That is cost prohibitive.

“if you have all 3 running on 200amp service it’ll trip the main.”

Possibly, but unlikely as I live alone except for when I have guests, and is easily avoidable then. And what would six do?

“I’m not quite sure I have a handle on the home layout though.”

It’s a single level so everything is spread out compared to my current house. Water heater is about the same distance from kitchen/ laundry room and bath off master bedroom. Other bathroom is about three times as far away.

“If you can find a central location plumbing-wise, I would have gone with a Ecosmart 27 (3.1gal/min) or a Stiebel Eltron Tempra 29 Plus (pricey). Amazon had a Gold Box on the Ecosmart a short while ago for $360, but it’s also come up 2-3x in the past year on their Lightning deals for around $370-390. These are also modulating units.”

OK. you like whole house tankless. I want the benefits of Point of Use. There is no waiting for hot water to get from distant heater to POU. There is no hot water left in lines between Whole House Heater to cool for nothing after I paid to heat it, which has always rubbed me the wrong way. There is maximum savings over a tank water heater. If one unit fails there is still hot water available in the house.

I’ll have to check my shower heads to see if they are 1.5 gpm and replace them if not. If there is a problem with the water not getting hot enough during a cold snap, I can always turn the tank heater back on for the duration of the extreme cold and have it at it’s lowest setting. Also I have three 5 gallon 110v tank heaters I could place at before the tankless ones. I am adept at the 10 minute shower so that would hopefully do it. If all that fails I will go with three Rheem RTE 13 units, which is what I had planned on doing before I saw these. It is sold as a WHH and ‘says’ it delivers 4gpm. That’s difficult for me to believe, but it’s Amazons best seller and the comments seem to support that for the most part, 4 of 5 stars.

I hope these will work for me, but I found little to go on before buying and took a gamble thinking they might sell out quickly as Woot items sometimes do. Never thought they would be around this long! If they are still here after I get mine I’ll post how they are doing. I plan to use a professional installer so if they say it won’t work, I’ll ask for a return. Woot has always been fair with me in the past.

+1 for being awesome enough to take the time to explain all this. Should be a quality post (it should count as two).

I meant use 2 inline for whole house, not using 1 of the 3 ordered.

No, I was trying to come up with a solution that was about the same cost of the 3 you ordered but could handle the heat output/gpm that met your needs. Given your original concern early on, it sounded like gpm/heat rise was the key concern.

You can attain that, but you have to go with larger units at each location. But then you run up against budget.

All a whole house or larger tankless unit is is their smaller ones inline and packaged as one unit. You can tell this by looking at the number and sizes of the breaker. If you have the space, that’s what people do, point of use with a larger “whole house” unit, e.g. master bedrooms with large tubs.

Save your money and effort. The Rheem should have no advantage in terms of heat output/rise over what you’ve already ordered here.

A 13kw unit from any competent manufacturer will deliver the same heat rise as another’s. It’s electricity, energy, it’s near 100% efficient, the ability to heat water will nearly be the same.

If the Atmor don’t meet the heat rise requirement, that particular Rheem won’t improve things.

The 4gpm figure is probably some max flow rate figure the unit detects and can handle, not the gpm it can heat. Rheem’s own table shows for that model 2.5gpm at 65deg inlet with a 105deg target temperature, which, without looking, sounded like what Atmor also states their unit handles. Even the higher 2.5 gpm is because the rise is less.