Electric tankless heater for one bathroom

[Pjkammer]

I'm planning a new bathroom build in western NY in an old house on well water. I'd like to install a tankless hot water heater that would only serve this bathroom (it will be the only plumbing on the 2nd floor of the house), but I'm not sure an electric unit will cut it. Obviously the ground water entering the house is cold, but we have a ~40 gallon pressure tank in the basement next to the furnace which seems like it would act as a preheat device. If the temperature of the basement pressure tank is ~60 F, could an electric tankless water heater be adequate?

 

[Twowaxhack]

I'm planning a new bathroom build in western NY in an old house on well water. I'd like to install a tankless hot water heater that would only serve this bathroom (it will be the only plumbing on the 2nd floor of the house), but I'm not sure an electric unit will cut it. Obviously the ground water entering the house is cold, but we have a ~40 gallon pressure tank in the basement next to the furnace which seems like it would act as a preheat device. If the temperature of the basement pressure tank is ~60 F, could an electric tankless water heater be adequate?

I’m working with a customer right now and her incoming water temp is 55 degrees and her electric tankless can’t keep up for a shower at 3gpm a minute at 105 degrees.

She has a Rheem Retex-18. It requires 2- 40 amp double pole breakers. It runs about 60 amps of power draw.

She’s not happy

 

[Twowaxhack]

I could tell today when the colder water from her crawlspace was purged and the warmer water from the city arrived at the water heater. It quit throwing an E5 code and was putting out barely enough to take a shower.

The city water was around 65 before it sits in her crawlspace piping and gets colder.

 

[Pjkammer]

It sounds like this isn't going to work for me. You don't think that it will have enough power to heat a shower (maybe 2-2.5 GPM) even drawing 60 degree water from the pressure tank?

 

[Twowaxhack]

It sounds like this isn't going to work for me. You don't think that it will have enough power to heat a shower (maybe 2-2.5 GPM) even drawing 60 degree water from the pressure tank?

How hot do you like your shower ? You tell me that and I’ll tell you if it’ll work.

 

[Mitchell-DIY-Guy]

What's the rest of the home use for hot water now? Do you have a hot water tank in the basement? Does that provide adequate temp and flow rates? You didn't indicate why you want to have a separate hot water system for this new bathroom build.

@Twowaxhack pointed out some data with his client and the RTEX-18. Rheem makes a number of other electric tankless heaters. However, that RTEX-18, shows 2 GPM with a 62 degree rise. In theory, that's sufficient for one continuous shower with cold water in, standard shower head, and maybe the bathroom sink running too. As he pointed out, the RTEX-18 needs 2 x 40A breakers, 240VAC. (I don't know if Rheem is a popular brand in the Rochester area, best to check around and see if they are. You probably don't want to use something not common the general area in case you ever need service, warranty or otherwise.) If the RTEX-18 seems "on the edge" for you, look at the upsized models from there which would be the -24, -27 and -36. Yeah they all use a LOT of electricity. Not uncommon for an "older home" to have 60A or maybe 100A incoming electric service. That -36 model uses 4 x 40A breakers, so if you don't have 200A service in the house, probably a no-go.

@Twowaxhack pointed out his customer that has the RTEX-18 and with 55 degree incoming water, isn't making her happy. Just goes to show you that the manufacturer specs probably don't reflect real world. According to the Rheem specs, his customer should be able to get a 2.0GPM shower and the temperature could be 117 degrees. Obviously somethings not right--specs overrated, or the client has a larger-flow shower head. Really doesn't matter, it's not right. So, if you are considering something in this realm, best to get a handle on the shower head flow rate.

So, taking his knowledge and experience with that same model, bump up to the larger ones and now you better own stock in Rochester's electric company. You'll need three or four 40A breakers.

https://s3.amazonaws.com/WebPartners/ProductDocuments/78DB9B79-53ED-43D5-92C3-BBFFD40F6F4B.pdf
One of the charts I saw on electric tankless had a map of the USA. Rochester NY was in the "consider a gas unit" area, as an FYI.

Our friends across the pond in UK love to have these things called "electric showers". Basically they are tiny tankless electric units that are INSIDE your shower area. At best you get lukewarm water in a navy-style shower. Not for American tastes.

 

[havasu]

There is something about seeing those electric water heaters inside my shower stall makes my skin crawl.

 

[Mitchell-DIY-Guy]

@havasu boy do you have that right! Growing up we were told "don't touch that switch when your hands are wet" and imagine my surprise when I traveled to Scotland in 2015, stayed in an old home that used to be a residence for Anglican priests or something, and found this "electric shower". Aside from the fact it could barely keep the water warm on the hottest setting, and the flow was merely a dribble, there's that high current, high voltage box on the wall IN THE &^%$ SHOWER STALL that just seemed so peculiar. But most of their plumbing is peculiar. No mixing faucets. Third-Degree burn hot water out of a tap on the left, ice cold water on the right tap. You want warm? Fill the bowl...with the rubber stopper. Toilets never clogged, since they were about a 5 gallon flush with a tank 10' high...I do suppose that modern home builds and related are up to what we consider modern standards but the older places are rarely updated if it works.

Right out of 1930s America.

 

[Twowaxhack]

With a thermostat setting of 120 and inlet temp of 60 degrees and a shower temp of 110 flowing @ 2.5 gpm requires 83% hot water. That’s 2.075 gpm of hot water delivered to the faucet mixer.

The Rheem Retex-18 @ 2gpm has a 61 degree temp rise. With an inlet of 55 flowing 2gpm the best you’ll get at the outlet of the water heater is 111 degrees water . But like you said, your incoming temp is 60, I hope you’re accurate and it’s stable.

In my case, factor in the heat loss through the piping, inconsistent incoming water temps and a shower that flows more a litttle more than 2.5 gpm and you get complaints. She’s just not happy.....

With a 60 degree STABLE inlet temp and a lower showering temp around 100-105 and a very short run from the water heater to the shower and you’ll probably be ok but it’ll be borderline.

 

[Mitchell-DIY-Guy]

...In my case, factor in the heat loss through the piping, inconsistent incoming water temps and a shower that flows more a litttle more than 2.5 gpm and you get complaints. She’s just not happy.....With a 60 degree STABLE inlet temp and a lower showering temp around 100-105 and a very short run from the water heater to the shower and you’ll probably be ok but it’ll be borderline.

PRECISELY. She needs a substation in her backyard, and the -24 or -27...maybe a propane tank would be a better solution, and gas fired. I surely understand when NG isn't available. Propane is costly, but so is electricity. I've inspected a lot of older homes, the kind of places where these kinds of "upgrades" sound plausible, but they simply do NOT have the incoming power to add them. Lots of older homes have 60A service, or 100A and no ground in the home. Some of the more modern homes, but still old, have 150. On these older homes, sometimes just adding central A/C to the home (much less an additional electric water heater) requires a new service panel, new drops from the service pole, a new meter, and it gets very costly for the people who live in these lower value, older homes, and they are the ones that can least afford it all.

My guess is, @Twowaxhack that you did NOT sell or install this "it's not making me happy" unit, but have been called up to "fix it".

Don't know where she found a >2.5GPM shower head but I'd love one...though I don't think my valve body would flow that.

 

[Twowaxhack]

Just take the flow restrictor out and if you have good pressure, you’ll be above 2.5 gpm.

No i did not install unit. Lady just bought house in July. Incoming water temps were 75 degrees then. She’s single and the only occupant. Just now started having trouble but it just got cold here, lows in 20’s/30’s and highs in 50’s/60’s

The most economical solution for her is a 40 gal electric . The electrician can convert to 30 amp 240 and I can install the tank in a couple hours. Around $1600 parts and labor. Gas tankless would be more than twice that installed $3800 unless I used outdoor model and hung on the house.

 

[hdtvkeith]

I researched tankless water heaters a few years back. My issue is my home was built in 1984. I have a gas dryer and 2 furnaces. To get a tankless that could deliver a good rate of rise when it was winter and the municipal water was cold required a unit that needed so much gas falls I would have had to repipe my gas lines. There are formulas for how large the gas pipe needs to be based on distance, bends and how many other gas devices are on the same line. I like 140F water so in winter than can means an 80+ rate of rise needed.

 

[Hamberg]

Throw another, electrical, piece in for the puzzle...

Like @Mitchell-DIY-Guy was saying, assuming the service has been upgraded to 200a and you have four slots open (2 x 2-pole 40a breakers), 125' of 8/3 nm copper is running ~$425 bucks! That is almost equal to the cost of the 18Kw tankless unit itself!

 

[hdtvkeith]

yeah being built in 1984 I have 150amp service and 2 EVs so adding any type of electrical draw is as bad as adding heavy additional gas draw.

 

[Hamberg]

yeah being built in 1984 I have 150amp service and 2 EVs so adding any type of electrical draw is as bad as adding heavy additional gas draw.

Sure one of the guys above mentioned this but I'd be leaning towards running the water lines (which you'll need to do either way) up and doing a supplementary tank. PEX would be relatively inexpensive, smaller tank, too and the electric could pull off a single 30a 2-pole - still pushing that 150a service to its max!

 

[hdtvkeith]

I went o upgrade service last year, as I have panel upgrade 6 years ago, but county said no go unless I move my panel as upgraded service needs to adhere to latest code and my panel location is no longer to code.

 

[Hamberg]

I went o upgrade service last year, as I have panel upgrade 6 years ago, but county said no go unless I move my panel as upgraded service needs to adhere to latest code and my panel location is no longer to code.

Interesting... (did they give you a) Reason it no longer meets code??

 

[hdtvkeith]

yes. There is a waste pipe from the upstairs bathroom that come down right over the panel. I may see about putting in some sort of deflector and see if county will approve that. It is just a hassle as most of the wires exit top of panel and many are right by that drain, so putting in a some type of deflector without moving the wires (no slack at all) will be a real pain.

 

[Hamberg]

...(no slack at all) will be a real pain.

Not envying you there! Short (no pun intended) of totally moving the service panel you may be able to use the existing box as a junction box for the circuits. Upgrade the service drop to 200A/250A, install the new service panel in an "approved" location and "junction" the circuits from there.

 

[hdtvkeith]

Not envying you there! Short (no pun intended) of totally moving the service panel you may be able to use the existing box as a junction box for the circuits. Upgrade the service drop to 200A/250A, install the new service panel in an "approved" location and "junction" the circuits from there.

Right now I really wanted 200A so I can charge both EVs at same time, right now they hang off a 60A sub panel and do power sharing. I would have preferred they each be able to pull their 40A concurrently.