Questions tagged [tankless]

A tankless water heater directly heats water on demand, instead of maintaining a reservoir of hot water. Use this tag in conjunction with the [water-heater] tag

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Will a tankless water heater be damaged by connecting to house hot water?

I bought an EcoSmart POU 6T tankless water heater. Can I run this as a hot water booster by connecting it to the house hot water line without damaging the heater? There is a similar answer here but I'...
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Why does my tankless gas water heater shut off when cold water is turned on?

When taking a shower, I have the hot water faucet full open. Then, if I turn on the cold water faucet on more than half way the heater shuts off. It will not start back up until the cold water is ...
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Repair a pinhole leak in tankless water heater

Its been a hard winter on plumbing, and I had some freezing pipes when I lost power for a few days and it was in the teens. The water was shut off but didn't drain the pipes. I had a pipe burst and ...
freshop's user avatar
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Is 200 amp service enough for a tankless water heater with a 100 amp sub panel?

We just upgraded out house service from 125 amps to 200 amps, and the house is all electric, no gas at all. The same day that happened my 41 year old water heater developed a leak and one of the ...
JBurt's user avatar
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15 votes
5 answers
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Why does my tankless water heater fail when the HVAC is running?

Florida, USA. 1963 or 1964 home. TL;DR: When my central (electric) heat is running, my A.O. Smith tankless (electric) water heater malfunctions. We purchased this home a few months ago. Over the last ...
samh's user avatar
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Navien NPE-A2 Recirculation Operation Details and Parameters?

Looking at the Navien NPE-240A2 Tankless Recirculating Water Heater Installation Manual there are several parameters of interest to me: Recirc Interval Time: Set the recirculation duration. (Default ...
Electro-Bunny's user avatar
1 vote
2 answers
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No hot water in barn apartment if wash stall hot water faucet left turned on, but turned off at the end of connected hose

We have a situation (along with two other new barn owners). Our new barn has a tankless water heater. Everything works great in the rest of the barn fixtures, if the wash stall hot water is turned ...
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Rinnai tankless feeding tank water heater

In my newly purchased home, I have an exterior natural gas Rinnai water heater that feeds into an interior electric tank water heater, which then feeds hot water throughout the house. In addition, ...
Anthony W's user avatar
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Would it be fine to use EMT to power a tankless water heater instead of flexible alternatives?

I recently had some plumbers install an exterior (natural gas) tankless water heater here in central Texas, in case the jurisdiction and / or climate matters. For the purposes of getting it installed ...
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Splitting 60 amp 2 pole to 3 -40 amp 2 pole subpanel

Can you split a 200 amp main circuit breaker box with a 60 amp 2 pole circuit breaker into 3 - 40 amp 2 pole circuit breakers in a subpanel for a tankless water heater?
GMalcom's user avatar
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1 answer
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Can I plumb a heat pump hot water heater in-line before a tankless hot water heater?

I remodeled a house a few years ago with a propane-fired Vitodens 100-b1KA Combination boiler/tankless hot water, but I got tired of the inconsistent hot water temperature and the exhaust venting into ...
Carson Michaels's user avatar
1 vote
2 answers
205 views

Wiring a tankless water heater in shed

I am installing a rheem RTEX-04 tankless water heater (120v 3.5kW) in a shed serviced by a sub-panel. the installation manual says connect black to a 30a breaker, green to ground, and leave the red ...
Rob's user avatar
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FLushing tankless water heater without hot water shutoff

I have a Bradford White RTG-K-199N1 tankless gas water heater. It has hot and cold water connections on top, and 2 flush valves at the bottom. I wanted to do a descaling flush, and the manual ...
Christian K's user avatar
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I have an Rinnai boiler/water heater, one zone. It worked well for 2 years and then began errors

Got E: 140 heat exchanger overheating. The propane company came out and replaced the internal circulator 2 weeks ago. Last night same error. they replaced it again but it still didn't work and they ...
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Tankless water heater furthest away room water [closed]

I have a tankless hot water heater and the 3rd floor of the house takes forever to get hot water. I was reading some kind of pump could be put in the 3rd floor bathroom to help move the water sitting ...
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Rancid smell using tankless water heater

We have had our tankless water heater for 5 years, within the last year we have noticed a bad smell coming out of exhaust pipe. The water heater was not vented through the roof instead it vented into ...
John Innes's user avatar
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Can I feed a mini, tankless hot water heater from an ultrafiltration water filter system?

I've just been diagnosed with a ubiquitous pulmonary bacteria called MAC commonly found in tap water and that requires a 0.2 micron filter. It's smaller than other bacteria and treatment is long and ...
Michael's user avatar
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Rheem KW-18 tripping breaker

I installed a Rheem KW-18 tankless water heater in the house 3-4 years ago. I have never had an issue other than the lights will blink when the water heater is running. We adjusted to that and it's no ...
Pete in NE Ct's user avatar
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1 answer
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Tankless gas water heater exhaust pipe

I installed a tankless gas water heater about 18 months ago. I used polypro for the exhaust pipe as I understand the MA code to require. The polypropylene exhaust pipe extends something like 12 inches ...
KRW's user avatar
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4 votes
1 answer
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Best solution for undersized wire/breaker?

I’m installing a Stiebel Eltron 24kW electric tankless water heater in my garage which requires two 50A breakers and 6/2 wire. I have a 200A sub panel located in the same garage (Siemens G3040L1200CU)...
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What size breaker box am I going to need?

I would like to use a Smith Four chamber electric tankless water heater it requires 240 V 60 A each on two circuits. Recommended wire size is six it will be located less than 20 feet away from the ...
Susan Burske's user avatar
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3 answers
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How should I connect a tankless water heater with four wires?

I just bought a tankless water heater for my house and removed my old tank water heater. I did note that with my new heater, it takes 4 wires my old tank only took one wire. Would I be able to make a ...
NAC CAN Nate's user avatar
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Sizing recirculating pump for water heater return line

Edit: According to Rinnai, the minimum flow rate is 0.26 GPM. I just replaced an old water heater tank with a Rinnai RU199 tankless unit. A dedicated 1/2 return line was ran through the attic to the ...
tripleblep's user avatar
1 vote
2 answers
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Tankless water heater in line with building hot water

Will a tankless water heater at a bathroom sink on the hot water line shut off once the hot house hot water reaches it?
Steve's user avatar
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13 votes
4 answers
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Should I replace two 75-gallon (gas) water heaters in series with a tankless heater?

We live in the Midwest in a large home that was built 20 years ago. At the time, we installed two 75-gallon gas water heaters, and the plumber did this in series, not parallel. We also have a system ...
Shelly Lee's user avatar
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Under-sink tankless water heater inlet

I'm looking at installing a mini water heater under my kitchen sink for quick usage. I already have a whole- house tankless water heater in my basement. I'm trying to avoid having the main unit kick ...
BigLake's user avatar
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2 votes
2 answers
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Is this temperature and pressure release piping up to code?

I just finished installing this Rennai natural gas tankless heater yesterday, and it's working well. My only question is I'm wondering that if I ever get it inspected, will this T&P release piping ...
ConcernedHobbit's user avatar
4 votes
1 answer
277 views

Where can I place a direct vent termination location for water heater?

Location: U.S. I'm trying to figure out all of the clearance distances requirements and looking for the best place to vent a new direct vent water heater. As you can see by the image, the existing ...
SlowSL's user avatar
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2 answers
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Is it ok to plug my 240v tankless water heater directly into a 50 amp RV plug instead of putting it on two 30 amp breakers

I live in an RV and am trying to install an electric tankless water heater by myself. It says it requires 2 double pole 30 amp breakers which is not really an option for me, the manual says the heater ...
RandaNae's user avatar
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2 answers
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Is Crossover Hot Water Recirculation a Good Choice for Branch-Type Piping Configuration

Is crossover hot water recirculation a good choice for branch-type piping configuration? I am considering replacing my aging hot water heater with a tankless. Several products offer a recirculation ...
jcropp's user avatar
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1 vote
4 answers
119 views

Tankless water heater supply configuration

I installed this Stiebel-Electron tankless. It was my first time sweating pipe, I enjoyed the process but I'm unhappy with the pipe alignment, the pipes angle with the heater is not truly plumb. I ...
tgk's user avatar
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1 answer
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tankless water heater low noise off and on all night

I just moved into a house with a new tankless water heater. It works fine when operating, but it seems to make a low humming noise off and on all night, when no one is using water. It is external, and ...
Joe B.'s user avatar
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3 answers
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Can I replace a 30 amp double pole breaker w/ 60 double pole breaker for tankless? Breaker is tripping

I replaced 28 gallon water heater: E1F30LD035V, with a tankless: https://a.co/d/1HokO6G. The tank was hooked up to 30 double pole breaker.. I thought that was good enough for the tankless, but it ...
Meg 's user avatar
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2 votes
2 answers
269 views

What is the impact of outside scaling on the heat exchanger of a tankless water heater?

live in the mountains. hard water. i descale 1-2 times a year. still, there is visual evidence of scaling on the outside of the heat exchange. proximate to the bottom gasket and the glass-window. ...
1c1cle's user avatar
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4 answers
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Can I split the cold water to get hot water (using a tankless heater) for a shower?

I have a small "casita" (a bedroom-size building separate from my house) where we want to add a bathroom (shower + sink). Since there isn't water in that structure we're planning on piping ...
JPJ's user avatar
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1 vote
5 answers
290 views

Can I replace a fried 60A tankless water heater wired to a double pole 60A breaker on 6AWG with a 40A tankless water heater?

Original tankless is a Eemax 13 Kw 60 A and the replacement is a EcoSmart 8 Kw requiring a 40A DP. Currently in our electrical box is a 60A DP. Do I need to swap this for a 40A DP or will the 60 A DP ...
needHOTwater's user avatar
2 votes
0 answers
83 views

Which Residential Electric Load multiplier is valid for water heaters and EV charging?

I know how to perform a residential load calculation using either: -(a) the Standard Method, which includes a 0.75 multiplier for fixed appliances (so, a 4500W water heater would be treated as adding ...
borisj's user avatar
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2 votes
0 answers
188 views

Possible causes for a gas tankless water heater sometimes shutting down

I have a Rheem ECOH2OODVLN gas tankless water heater. I'm not sure of it's exact age as it came with the house, but it's in good condition (clean, no dust, no visible damage, etc.). The situation: ...
Erick T's user avatar
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0 votes
2 answers
148 views

3x 100 gallon propane tank on 3 family building

I'm a new owner of a 3 family apartment building with 3 100 gallon propane tanks for heating and hot water for each unit. All 3 units have Navien tankless hot water heaters. I'm thinking about getting ...
Tasia Ojeda's user avatar
0 votes
2 answers
169 views

Tankless with a tanked hot water heater

I have a RV that I live in full time and I added a tankless in line with the factory tanked hot water heater (for trips or future plans I am leaving the tanked). I am having an issue of I can use up ...
Brandon Sparks's user avatar
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2 answers
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Hot water works only 10% of the time in kitchen faucet, works fine in other sinks

My kitchen sink hot water works inconsistently and mainly doles out cold water. However, if I turn the hot water in the bathroom sink the hot water starts working in the kitchen sink so I’ve just been ...
Luna's user avatar
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4 votes
3 answers
2k views

What kind of putty should be used for sealing rim joist exhaust vent holes?

I recently had a tankless water heater installed in my basement. The 4" exhaust vents through the rim joist. I'd like to seal the gap around the PVC, but I'm uncertain what type of putty to use. ...
Parker's user avatar
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1 vote
1 answer
285 views

Home Heating - Oil Boiler vs Propane Tankless

My house has redundant systems for both domestic hot water and hydronic heating (baseboard and radiant floor). I can pick and choose which system I'm running. We also have several mini-split heat ...
anders's user avatar
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1 vote
1 answer
506 views

What is causing my brand new tankless water heaterto knock?

I just had a Navien tankless water heater installed. It works fairly quietly when in use, but there is a knocking sound from the unit or the copper pipes hours AFTER it has been used (typically in the ...
Claude's user avatar
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1 vote
2 answers
174 views

Retrofit tankless installation in an apartment building with rooftop solar

This is hypothetical, but based on a real case. A landlord has an apartment building with 20 units. There is a single 150-gal gas water heater in the building that serves all the units. The landlord ...
tavr's user avatar
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0 votes
0 answers
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How should I secure T&P relief valve discharge copper pipe to the wall?

The copper pipe is the T&P relief valve discharge pipe and the white pex is for condensate. What's the correct way to secure this pipe to the wall?
CaptainUnderpantsOnly's user avatar
7 votes
4 answers
6k views

Do tankless water heaters have a maximum temperature limit for the incoming "cold" supply water?

I currently have a tankless, natural gas hot water heater on the side of my house. I want to preheat the incoming water using a solar water heater. Is there any concern with having the input supply ...
Jon's user avatar
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1 answer
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Where should I install a Kolerflo 120W water pressure booster pump?

I have a tankless water heater and the water pressure is not enough to turn the tank on demand causing the water in the shower to be just barely warm. I purchase a Kolerflo 120W to boost the pressure, ...
David's user avatar
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0 votes
1 answer
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Okay to use cold water drain valve on tankless gas water heater as a spigot?

I need to use a pressure washer outside my house, but there's no spigot nearby. I do have my tankless gas water heater nearby though, which has drain valves (both hot and cold). When I opened up the ...
K. Don's user avatar
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0 votes
0 answers
444 views

Do I need to flush my tankless water heater annually?

I bought a Rheem tankless water-heater last year, it is RTG-95XLN-1 model. I was told that I need to flush it using vinegar and circular pump at least once a year, to prevent sedimentation. There are ...
A.Magnus's user avatar
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