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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
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

Do point of use water heaters shut off automatically in the inlet temperature is too hot

Edit: there is a hack where it can work, but it requires convenient piping layout and limited flow. The general problem with tankless is the faster the flow, the more electricity you need. You need a ...
Harper - Reinstate Monica's user avatar
7 votes

Do point of use water heaters shut off automatically in the inlet temperature is too hot

Probably the reason you can't find the answer is because it depends on the point of use tankless water heater. There are some smaller 120 Volt units, 3600 Watts, that do not have thermostatic control. ...
JACK's user avatar
  • 82.1k
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
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
5 votes

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

Call the power company and explain the problem. I had a similar call from a homeowner and it ended up being corrosion in an electrical junction(?) box outside of the house, off of the property
Doitall's user avatar
  • 51
5 votes

Tankless gas water heater exhaust pipe

248 Mass. Reg. 5.12 says: Plastic Piping. The only plastic piping which may be used for venting appliances shall be CPVC, polypropylene, and other pipes which have been Product-accepted for that ...
MTA's user avatar
  • 11.4k
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
4 votes

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

Oh man! so I guess you got an electric tankless WH. They take a LOT OF POWER. I'm thinking you are using the term wire and cable interchangeably. A wire is an individual conductor, a cable can ...
George Anderson's user avatar
4 votes

Do point of use water heaters shut off automatically in the inlet temperature is too hot

Most point-of-use water heaters are designed for exactly this use case, and do have thermostats that turn off when the incoming water is already hot enough. This does require setting the point-of-use ...
jpa's user avatar
  • 1,564
4 votes
Accepted

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

I don't know if this is the cause of your problems... But I wonder if a screw driver, some ox guard and 10 minutes to plug in a cable would help. One thing that has bothered me about this picture ...
Questor's user avatar
  • 906
4 votes

Why does my tankless gas water heater shut off when cold water is turned on?

We had this same problem with our Bosch gas fired tankless water heater (WH). There are different ways to fix this depending on your situation. What is happening is that you are using such a low flow ...
Jim Stewart's user avatar
3 votes

Repair a pinhole leak in tankless water heater

I finally got this repaired, after 5 failed attempts. Here are a few notes: Had to get the copper really heated up. Propane torch didn't make it hot enough I had to use MAP gas Heated for like 2 ...
freshop's user avatar
  • 1,916
3 votes
Accepted

Would it be fine to use EMT to power a tankless water heater instead of flexible alternatives?

As you describe the situation, I would not hesitate to use EMT. You likely already have or could have a rigid gas line connected to the heater. The manual does not specify a conduit type. I'm not ...
KMJ's user avatar
  • 12k
3 votes

Splitting 60 amp 2 pole to 3 -40 amp 2 pole subpanel

NO! If I understand correctly, you want to use a 60A double-breaker to feed a subpanel with 3 x 40A double-breakers. There are certain situations where you could do that, but not for tankless water ...
manassehkatz-Moving 2 Codidact's user avatar
3 votes

Tankless water heater furthest away room water

A tankless water heater is designed to sit there doing nothing (and saving energy by doing nothing) until the rate of water flow in the hot water pipe reaches a certain minimum value. Then it switches ...
MTA's user avatar
  • 11.4k
3 votes

Wiring a tankless water heater in shed

I don't know where you got those instructions from. They are close to the right stuff, but wrong in many small but critical ways. I found a much better manual for the RTEX-04T at Home Depot. There are ...
manassehkatz-Moving 2 Codidact's user avatar
2 votes

What size breaker box am I going to need?

SMH everybody's hatin' on tankless. That's not fair. Tankless works fine and is actually more efficient and takes less total power. The problem is tankless is ruthlessly unforgiving to foolish ...
Harper - Reinstate Monica's user avatar
2 votes

What size breaker box am I going to need?

If you REALLY want to do electric tankless water heaters for both domestic hot water and space heating, you will need to do a load calculation...big time. My best guess would be you'd need 2 (yes ...
George Anderson's user avatar
2 votes

Wiring a tankless water heater in shed

First an aside. Your subpanel is set up incorrectly. As of NEC 2008, it must have a separate neutral and ground wire going back to the panel. Plus the 1 or 2 hot wires. If it is an outbuilding, it ...
Harper - Reinstate Monica's user avatar
2 votes
Accepted

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

As usual there is a temperature probe on the inlet, and a pressure sensor on the outlet. If it is smart it will adjust heating power depending on inlet temperature, but there will be a delay until the ...
bobflux's user avatar
  • 10.1k
2 votes

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

Unfortunately some require that frame challenges be labeled. This is a frame challenge. Yeah, the problem is that 85F tepid water sucks a lot more than you think in a shower. You won't enjoy it. But ...
Harper - Reinstate Monica's user avatar
2 votes

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

To try to determine whether you can get the existing equipment to work for you, determine if the fault is occurring only at the startup of the HVAC heat pump. Lower the thermostat on the HVAC to cause ...
Jim Stewart's user avatar
2 votes

Can I plumb a heat pump hot water heater in-line before a tankless hot water heater?

Yes. I setup a 3 hpwt pre-heat system before a 180k btu gas hot water tank. Used the rheem proterra 80 gallon tanks. Set the hpwt to heat pump only mode. The system used to be 2x 180k gas btu tanks. ...
Fresh Codemonger's user avatar
1 vote

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

I’d be more likely to have gas service installed at this point. That would in fact fix both the tankless (switching from electric to gas) and the auxiliary heat for the heat pump. Note that a heat ...
mdfst13's user avatar
  • 460
1 vote

No hot water in barn apartment if wash stall hot water faucet left turned on, but turned off at the end of connected hose

You are going to have to shut off the water at the mixing faucet in the barn when not washing a horse--you can't just leave the hose nozzle shut off and the faucet valve(s) open. You will be able to ...
Jim Stewart's user avatar
1 vote

No hot water in barn apartment if wash stall hot water faucet left turned on, but turned off at the end of connected hose

When other faucets call for hot water, cold water is flowing through the hose connections (or mixer) into the hot supply instead of flowing through the heater. Fit a check valve before the hot supply ...
Jasen's user avatar
  • 21.6k
1 vote

Rinnai tankless feeding tank water heater

I found this post from a few years ago that has many different opinions and pros-cons of using a tank AND tankless water heater, which was very helpful. It seems there's no "right" answer to ...
Anthony W's user avatar
1 vote

Can I feed a mini, tankless hot water heater from an ultrafiltration water filter system?

With a 0.2 micron filter, the pressure loss and therefore the water flow will be very low. While, theoretically you can feed the dishwasher and the tap/faucet, practically, it is unlikely to work. ...
Rohit Gupta's user avatar
  • 6,550

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