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25 votes

Can tankless & conventional water heaters join forces?

I see a couple problems there. First, having a tanked heater operate at less than 140°F (60°C) is problematic. The reason is our science has advanced on the Legionella bacteria which causes ...
Harper - Reinstate Monica's user avatar
23 votes

Want to switch to tankless, but can I use my existing wiring?

If a heater requires 8 AWG wire, it's because it requires more electricity than a smaller wire is capable of safely delivering. If you used the 12 AWG wire, first the 20A breaker would trip, but if ...
JPhi1618's user avatar
  • 27.9k
22 votes

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 That is the correct way ...
Harper - Reinstate Monica's user avatar
19 votes

Why does my tankless water heater fail when the HVAC is running?

In the words of Captain Kirk, We need more power! Update cancelled because OP commented that they have now verified the manual actually calls for 2 x 60A. All other issues of total load capacity still ...
manassehkatz-Moving 2 Codidact's user avatar
16 votes

Should I replace two 75-gallon (gas) water heaters in series with a tankless heater?

Option (0) would appear to be to "address this" by fixing the defective installation, without replacing anything major, since it's very likely an installation problem or a simple part ...
Ecnerwal's user avatar
  • 217k
12 votes
Accepted

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

A Rinnai tankless gas water heater does indeed have a temperature sensor and regulates the outgoing hot water temp. based on incoming water temp. So the burner in the Rinnai has the ability (and the ...
Kyle's user avatar
  • 4,843
11 votes
Accepted

Can tankless & conventional water heaters join forces?

Your gas pipe plan seems reasonable -- 1" pipe carries a lot of CFH of gas. We'd have to know the pipe length involved to be sure, but it's likely that covering most of the distance with 1" will keep ...
Greg Hill's user avatar
  • 30.8k
10 votes

Is 200 amp service enough for a tankless water heater with a 100 amp sub panel?

Let's see. 5.5 GPM at 8.35 pounds per gallon, so 46 pounds per minute. 2755 pounds per hour. To raise 1 pound of water 1 degree F takes 1 scientific BTU ( not to be confused with the commercial BTU ...
Harper - Reinstate Monica's user avatar
9 votes

Want to switch to tankless, but can I use my existing wiring?

You cannot use an electric tankless water heater in place of an electric tank without a significant upgrade in wiring and most probably adding new breakers to make a total of two or three breakers. ...
Jim Stewart's user avatar
  • 21.9k
9 votes

Can/should I change GFI outlet to standard outlet

Maybe others will chime in, but I don't understand why the instructions would recommend against using a GFCI outlet other than for reducing the possibility of nuisance trips. Perhaps they are ...
George Anderson's user avatar
9 votes
Accepted

Should I replace two 75-gallon (gas) water heaters in series with a tankless heater?

A completely different cause (unrelated to the water heaters) might be failed anti-scald valves in one or more of various fixtures around the house. Due to design of such valves, the fixture does not ...
Ecnerwal's user avatar
  • 217k
8 votes

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

So the water heater installers had a beaver or squirrel on the crew to gnaw a hole, rather than using hole-saws like competent workers? Ugh. I'd wrap that tightly in a scrap of plastic (housewrap or ...
Ecnerwal's user avatar
  • 217k
7 votes
Accepted

Electric Water Heaters: Tank vs Tankless (Instant On) Energy Usage?

...in a modern tanked heater with modern levels of insulation, and people actually using hot water from time to time, standby losses are microscopic .vs. use. So a tankless electric is a very ...
Ecnerwal's user avatar
  • 217k
7 votes

Installed Electric Tankless Water Heater - Internet loss when active

First, make sure that your three supply cables are paired properly. The unit has 3 heaters internally. There are several ways cables could be crossed that would result in power from 1 heater coming ...
Harper - Reinstate Monica's user avatar
6 votes

16" center bracket to 24" center framing

The other answer given so far describes a solution where the tankless water heater is being installed in an area where the studs are open and not covered. There are instances where the studs are not ...
Michael Karas's user avatar
  • 65k
6 votes

Can tankless & conventional water heaters join forces?

You can run water heaters in series. There's no problem there, typically. Consult the installation manual to be sure. Your main concern is probably efficiency. While it stands to reason that your new ...
isherwood's user avatar
  • 139k
6 votes

Can/should I change GFI outlet to standard outlet

TL;DR Safe answer = Hardwire There are a few different pieces here: GFCI affects stuff That is, IMHO, almost entirely mythical. GFCI is, as I understand it, a basically passive system unless/until it ...
manassehkatz-Moving 2 Codidact's user avatar
6 votes
Accepted

Shower gradually cools, gets hotter when sink is on. Navien tankless whole house HWH

Problem solved I deduced that the recirculation pump backflow valve inside the HWH must be broken. The water at the shower cools because it is pulling water from the HWH "hot" side and also ...
brfox's user avatar
  • 416
6 votes
Accepted

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

That kind of putty is called “duct seal” and you can get it pretty much any hardware store, big box hardware stores, electrical supply shops, etc. it will work fine.
RibaldEddie's user avatar
  • 2,420
6 votes

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

This is wrong in many ways: Instructions are based on UL/ETL/etc. determination of the safe way to power and install the device. In particular, when a large power device moves from 1 circuit to 2 ...
manassehkatz-Moving 2 Codidact's user avatar
6 votes

How should I connect a tankless water heater with four wires?

Sounds like you fell for the hype of tankless. Most of the marketed "benefits" of a tankless heater are misleading at best. Instant hot water only happens when it's a point of use heater or ...
ratchet freak's user avatar
6 votes

What size breaker box am I going to need?

A tanked water heater is superior to tankless in every way other than how much hot water you get at once. A hot water tank is a battery that you can can charge slowly (even overnight at lower rates). ...
ratchet freak's user avatar
5 votes

Installed Electric Tankless Water Heater - Internet loss when active

Long shot...if I'm wrong I'll delete. 112 Amps is a HUGE draw. As you probably know, many houses have a total 100 Amp (sometimes less) service. If your service drop isn't significantly larger, or ...
manassehkatz-Moving 2 Codidact's user avatar
5 votes
Accepted

Installed Electric Tankless Water Heater - Internet loss when active

Something you might want to consider here is that your phone line inside the house is probably something crappy and unshielded. Cat3, for instance, offers virtually no shielding at all. What I would ...
Machavity's user avatar
  • 24.9k
5 votes

Can tankless & conventional water heaters join forces?

I would use the new tankless heater for the rooms you use most often and the existing tanked heater for guest rooms. It's more plumbing work but it gives you the best of both worlds. You can switch ...
Level River St's user avatar
5 votes
Accepted

How to connect flex NMC to Rinnai tankless

OK, so I called the support line, and to my (pleasant!) surprise, they were willing to talk to me, a mere homeowner. Running the power cord up through the grommet is intended. But the gentleman also ...
Kerry Thomas's user avatar
5 votes

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

The tankless doesn't have a valve to block flow. So the pre-hot water will roll right through it. It'll add heat if it's under-temperature. This means the water could be scalding! Tankless heaters ...
Harper - Reinstate Monica's user avatar
5 votes

Retrofit tankless installation in an apartment building with rooftop solar

Given the described situation, would it make sense to install a high-capacity electric tankless water heater upstream of the 150-gal? All schemes which place a tankless heater in series with a tanked ...
Harper - Reinstate Monica's user avatar
5 votes

Can I replace a 30 amp double pole breaker w/ 60 double pole breaker for tankless? Breaker is tripping

You will have to replace the wires from the panel to the heater too. A 30 amp breaker probably has #10 AWG connected to it which is only good for 30 amps. Your new heater will require 54 amps which ...
JACK's user avatar
  • 81.7k
5 votes
Accepted

Best solution for undersized wire/breaker?

Load Calculations are mandatory The procedure that must be used is described in NEC Article 220. Dwellings may use the alternate method in 220.82. The electrician will require this anyway. Note ...
Harper - Reinstate Monica's user avatar

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