The Best Tankless Water Heaters

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Tankless water heaters, also known as on-demand or instant water heaters, have many advantages over traditional tank-style water heaters and they can be an excellent long-term investment.

Unlike traditional tank-style water heaters, which continuously use energy to maintain a hot water supply, tankless water heaters only expend energy when you turn on a hot water tap or when your appliances demand hot water.

Besides energy and cost savings, there are several other reasons to choose a tankless water heater over a traditional tank-style heater:

  • Endless supply of hot water
  • Space-saving
  • Lower risk of leaking
  • Generally safer
  • Significantly longer lifespan on average.

There are different types of tankless water heaters based on their installation (outdoor or indoor) and based on the energy they use (propane, natural gas, or electricity). In general, gas heaters produce better hot water flow than electric heaters but of course, your house needs propane or natural gas supply.

Check Before Buying

First, the type of heater you need.

 Is your gas supply line capable of properly feeding it with gas?

Is your electric power supply sufficient?

Does your water supply system have good enough water flow?

Our picks for the best tankless heaters are the Rheem RTGH-84DVLN Indoor Direct Vent Natural Gas Condensing Tankless Water, and the Rheem 240V 4 Heating Chambers RTEX-36 Residential Tankless Water Heater.

The Best Tankless Gas Heaters

Rheem RTGH-84DVLN Indoor
Direct Vent Natural Gas Condensing
Tankless Water Heater Low Nox


Indoor Direct Vent Natural Gas Condensing

Tankless Water Heater Low Nox

Rheem RTGH-84DVLN is a natural gas tankless water heater. It has a built-in electric blower supplied with a 120V power cord, freeze protection to -30°F, and a flow rate of 8.4 GPM. Its size is 9.79×18.5×27.5 and it weighs 77.9 pounds.

Why is the Rheem RTGH-84DVLN our favorite?

This unit is capable of delivering 8.4 gallons per minute of hot water flow. This means you can use three showerheads and two faucets or two shower heads, a dishwasher, and a washing machine simultaneously. It can pretty much replace the most common 50 gal water heater.

Rheem RTEX-36 is an electric tankless water heater that features external digital thermostatic control with 1°F accuracy, advanced self-modulation (adjust power to meet hot water demand), durable copper immersion four heating elements, bottom ¾ inch NPT water connection, flow rate 8.0 GPM. Its size is 4x22x19 inches and weighs 22.7 pounds.

RTG-84DVP is a propane tankless water heater that features a minimum flow rate of 0.26 GPM, 0.4 GPM minimum activation flow rate, includes UMC-117 remote control, and 10ft of thermostat wire, and 8.4 GPM flow rate. Its size is 9.87×13.87×2362 inches and weigh 62.5 pounds.

This unit has the same flow rate as RTGH-84DVLN but is much cheaper and weighs around 15 pounds less. This makes me think that it’s missing some features compared to RTGH-84DVLN. Looking at the product description, it’s probably that built-in electric blower.

Rheem RTEX-24 is an electric tankless water heater that features on-demand continuous hot water flow, digital temperature control in increments of 1°F from 80°F to 140°F, 99.8% energy efficiency, robust copper immersion heating elements with brass top, simple installation, digital temperature display, and 5.9 GPM flow rate which is a lot less than that of RTEX-36.

Here’s a reference of approximate flow rates of common fixtures and appliances: Bathroom sink 0.5 GPM, washing machine 1-1.5 GPM, kitchen sink 1-2 GPM, dishwasher 1-2 GPM, shower head 2.0 GPM, and bathtub 4.0 GPM.

Why trust us?

We’ve managed and maintained over a thousand rental properties. For this buyer’s guide, we also spoke to our plumbing vendors to make sure we are giving you the best possible recommendation.

What are the downsides of a tankless water heater?

They are not really instant

Tankless water heaters are also known as on-demand heaters because they work only when you open a faucet or some of your appliances demand hot water.

Although many people call them instant water heaters, they are not really instant. Depending on the location of the heater, the temperature of the water that enters the heater, the condition of the plumbing system, the water flow rate, you may end up waiting a couple of minutes or more for the hot water to reach the faucet.

You may have to install a water softener

IF the water in your area is too hard, you may need to install a water softener because otherwise, calcium buildup will eventually cause the heater to malfunction and even break.

If there is a problem with the water flow caused by clogged pipes or something else, the heater ‘thinks’ that there is no hot water demand and shuts down

Inconsistent water temperature

If the faucet is too far from the heater sometimes the water starts running hot, then cold, then hot again, and so on (known as the cold water sandwich effect). This happens because to regulate the temperature, the heating element or the gas burner constantly turns on and off and if the faucet is too far away from the heater, the hot water cools down inside the pipes between those cycles.
Inconsistent water temperature also happens if the demand on the heater is high.

No hot water during blackouts

During a blackout a tank-type heater will still have tens of gallons of hot water that you can use while a tankless one will stop immediately.

Is a tankless water heater worth it?

It all depends on the area you live in, the water quality and temperature, the condition of your house’s plumbing, the size of your house, and the number of fixtures you need to supply with hot water.

How much does it cost to have a tankless water heater installed?

All manufacturers have a list of contractors that are eligible to install their products. You can install it by yourself or get it done cheaper by your local plumber but it will void the unit’s warranty.

Installation prices vary from area to area and all contractors have different prices, but in general, you need to be prepared to pay as much as for the unit itself.

Can you run out of hot water with a tankless water heater?

That’s the big difference between tankless and tank-type water heaters. If your tankless heater meets your home’s hot water demand and there’s no power outage, this should never happen.

You may see inconsistent water temperature if the demand is too high but you will never run out of hot water. If there’s a power outage, tankless heaters stop immediately while tank-type heaters will have enough hot water in them to finish what you’ve started.

What size tankless water heater do I need for a family of 2?

Usually,  a tankless water heater with 4-5 GPM (gallons per minute) water flow rate should be enough for 2 people but it all depends on your habits of using hot water. The list below will help you calculate the size of the unit you need according to the number of fixtures in your home and how many of them will eventually work simultaneously (all water flow rates in the list are average):

  • Bathroom faucet: 0.5-1.5 GPM
  • Kitchen faucet:  1-2 GPM
  • Shower: 2-3 GPM
  • Bathtub: 4-5 GPM
  • Dishwasher: 1-2 GPM
  • Washing machine: 2-3 GPM

Should I buy a tankless water heater if I have hard water?

Hard water builds up calcium inside the heater’s components (pipes, heat exchanger, valves, etc.) This significantly reduces the unit’s life, makes it work harder thus using a lot more energy, randomly fail to turn on, and finally break.

If you live in an area with hard water but you are determined to install a tankless water heater, you will need to install a water softener as well. Actually, most of the manufacturers will ask you to do so if you don’t want the unit’s warranty to be voided.

Can I install a tankless heater if I am on well water?

In general, well water is not different from municipal water. First, you need to be sure that your well pump works properly. All well pumps have pressure gauges where you can see what’s the water pressure in your pipes (40-50 psi).

Next, determine if the water in the well is soft or hard. A good indication for hard water is calcium buildup on the faucets inside the house but you can just do a soap test since hard water doesn’t react with soap as well as soft water; however, the best option is to call an expert for a professional water test.

If it turns out that the water is hard, you will have to install a water softener. There are some myths going around that well water is too cold or doesn’t have enough water flow or pressure. Definitely not true. Well water is not colder than the municipal water since the supply lines are installed in the same depth underground. Also, well pumps are designed to supply your house with constant water pressure and water flow.

About the author

Chris Christo owns a property maintenance company and writes for Rentce on all rental maintenance topics.
He is also a rehabber and a landlord.
When he doesn’t work on properties or writes about properties, he can be found fishing.