Tankless Water Heater FAQs

Q&A on how to buy, install, adjust or repair Demand / Instantaneous / Endless Hot Water Systems

Tankless Water Heater Maintenance FAQs

How to drain the Rheem tankless RTE 13 water heater for winterizing

I just bought a Rheem RTE 13 with supply and outlet pipes on the side of the box.

For winterizing a cabin against freezing, how do I drain the water left inside the tank. - Anonymous

Reply:

The Rheem Tankless Electric RTE 13 is a tankless water heater. There is no "tank" to drain. However there will be water in the coiled copper tubing inside the water heater that must and can be drained via service valve found at the bottom of the coil inside the unit.

Continuing: if you don't have a service and installation manual for your water heater or if you need more assistance

Manufacturer’s National Service
Department at the following address:
1241 Carwood Court
Montgomery, Alabama 36117
Phone: 1-800-432-8373.

When contacting the manufacturer, the following information will be requested:

a. Model and serial number of the water heater as shown on the rating plate attached to the jacket of the heater.

b. Address where the water heater is located and physical location.

c. Name and address of installer and any service agency who performed service on the water heater.

d. Date of original installation and dates any service work was performed.

e. Details of the problems as you can best describe them.

f. List of people, with dates, who have been contacted regarding your problem.

Watch out: DO NOT TURN ON THE WATER HEATER AGAIN when de-winterizing it and restoring it to service until you have made certain that the heater has been completely re-filled with water and air has been purged from the system.

Finally, you can contact Rheem directly\

Rheem Water Heating and Heating & Cooling Products
101 Bell Road • Montgomery, AL 36117-4305
1-866-720-2076 • www.rheem.com

Rheem Canada Ltd./Ltée • Water Heater Division
125 Edgeware Road, Unit 1, Brampton, Ontario L6Y 0P5

Tankless Water Heater Installation FAQs

Tankless Water Heater Share Existing Gas Flue & Chimney?

Can my tankless water heater share an existing gas furnace vent pipe and chimney?

We are replacing a gas water heater in California and are considering replacement with a tank less. Currently, the water heater is located in an indoor utility closet that is shared with a gas furnace.

My question is, can the tankless water heater share the vent pipe with the furnace?

This is currently the case. The vent pipe is double wall and vents through the roof. - Anonymous · Sept 15, 2022

Reply by (mod)

@Anonymous,

It might be possible to share a flue provided that the total venting requirements can be met by the size of the existing one.

You need to check the total input BTUh of the combined heating appliances to be sure the flue can handle both appliances venting simultaneously.

When calculating whether or not a flue vent connector (connecting the appliances to the chimney) and the chimney flue are big enough, the chimney height is also a factor.

And of course, check the installation manual to see if the manufacturer permits it.

You'll find detailed guidance and chimney sizing tables at

CHIMNEY FLUE SIZE SPECIFICATIONS_TABLE_C_9_E - Multi-Appliance BTUH Venting Capacity of Double-Wall B-Vent Chimneys

and at

CHIMNEY FLUE SIZE SPECIFICATIONS TABLE 504.2 

where we give tables for chimney sizing based on input BTUh and fuel type and chimney materials type. - Daniel Friedman

Cost to put in a larger circuit breaker for tankless water heater

I am thinking about buying Rheem tanklesss water heater.

Rheem says I need a 4x40 breaker. My breaker says 30. Qbout whould it cost to change this? On 2019-01-06 by Anonymous -

Reply by (mod) -

Prices vary depending on where you live but you can figure 100 US dollars or less for a multi pole 40 amp circuit breaker and another $200 or more to pay an electrician to install it.

In larger cities where electrical work is more costly, adding a 40A or 50A circuit, run from the panel to the water heater location, can cost as much as $700.

Important also are the electrical wire run length and ease of access to run the new circuit.

The work is actually trivial.

Watch out however to be sure that you understand the correct breaker that's required. I don't know what a 4 x 40 breaker is.

Typically for a 220/240VAC electric water heater you'd install a 40A or 50A 240VAC circuit with a double pole 240VAC 40 Amp circuit brea,er.

Which hot water source is better, gas or electric?

I am thinking of replacing our hot water tank: which is best gas or electric? would prefer electric to avoid venting - Sid Archer 10/7/12

Reply:

Sid there is not a single right answer to which type of water heater is best, as you want to match the heater to the intended use.

Depending on where you live, electrical rates may make gas fuel look less costly to operate, possibly more costly to buy and install, including cost of a chimney or vent system.

Electric water heaters are generally lower in cost to buy and install but in at least some parts of the world, electricity rates can make their operation more costly than a gas, oil, or solar water heater.

Relief valve requirements for tankless water heaters

(May 11, 2015) Anonymous said:
Dose a gas tankless water heater require a pop off valve?

Reply:

Good question Anon.

Some tankless water heaters such as the POWERSTAR AE7.2 Point-of-Use Electric Tankless Water Heater and also the Rheem Tankless Electric RTE 13 are advertised as not requiring a pressure/temperature relief valve, but even there the manufacturer notes that the TP valve may be required by local codes.

But certainly there are tankless heaters that are installed with the valve and that include it OEM. And there are TP valves designed for these heaters such as the Rheem AP12993C Pressure Relief Valve and the Watts Model 3L TP valve. So the answer, as Mark Cramer says, is ... It depends...

Though it's always safe and not harmless to add a properly-located TPR valve.

Give us the brand and model number for more details.

Tankless Water Heater Diagnosis & Repair FAQs

Why does my pressure and temp drop in the shower when another faucet is used with hot water.

Why does my pressure and temp drop in the shower when another faucet is used with hot water.

Have on demand instant water heater. Plenty hot at sink and no heat and loss of pressure at shower. On 2018-01-29 by Robert -

Reply by (mod) -

It's an interesting uncommon problem about what you asked.

Demand water heaters or tankless water heaters have limited flow rate.

So when the hot water flow demand is increased by opening an additional faucet you're simply diverting some of the hot water to another location and reducing the flow at each.

Take a look at the installation manual for your water heater and you may note something interesting. The manufacturer often recommends specific dedicated water supply piping

To maximize the input flow rate at the water heater. so particularly in older homes where the water heater is a retrofit we often find that the input to the water heater is quite Downstream from the supply source and That may limit the hot water flow rate out of the heater.

You can increase the water pressure to increase the flow but of course if you exceed the rated input flow rate for your particular water heater your water may not be hot enough.

It's also possible that the heating coil could be partially blocked by scale. If that's the case descaling will significantly improve the water flow.

Water pressure problems with tankless water heater

I recently installed an electric (120 amp) tankless water heater in a cabin - it actually has 6 ganged heating coils that turn on incrementally as the demand dictates. I also installed a scald less shower faucet - which (I think) decreases the hot water draw when water pressure decreases.

My dilemma is: two or three times during a typical shower, the water temperature will increase rapidly (too hot), and then decrease rapidly (too cold) - and then settle at the "agreed upon" temperature for a minute or two. The water system is on a residential well that uses a 40-60 lb pressure switch.

I theorize that when the pressure approaches the low (cut-in) point, the faucet demands more hot water (which causes the tankless heater to crank up more heating coils), but about the time that new hotter water reaches the shower (about 13 seconds from the water heater to the shower head) the pressure increases toward the 60-lb (cut-out) range - causing the faucet to demand less hot water - causing the water heater to shut down some of the heating coils.

So, If I set a closer differential between the pressure switch cut-in/cut-out pressures (like maybe raising the cut-in to maybe 50 lbs), could I eliminate that yoyo effect? Or could there be a different cause? - Cabin Jack 1/19/2012

Reply:

Jack, Why not install an automatic mixing valve to regulate the temperature regardless of water pressure?

Also see TANKLESS WATER HEATER REPAIR GUIDE where we discuss other reasons that hot water temperature may vary when using an instant or tankless water heater.

No water comes out of new tankless water heater

I have a tankless hot water heater it has no pressure on the hot water side it’s brand new cold water side has good pressure.

I have never turned it on yet it’s electric also change the inline filter what could be wrong ? On 2018-09-13 by Keith -

Reply by (mod) -

When there is absolutely no water output from your new tankless water heater, and if we can assume that you made proper plumbing connections, I would start by looking for valve that's closed on the hot or outlet side of the heater.

Don't forget to check the service valves on your inline water filter.

Less likely but possible: on occasion I've seen new plumbing work using soldered copper pipe connections at which the intaller used too much solder, pushing so much solder into a connection that the solder blob blocked the pipe.