Can You Have Both Tank and Tankless Water Heater?

Can You Have Both Tank and Tankless Water Heater?

Note: As an amazon associate I may earn a small commission from qualifying purchases if you click to amazon from my site and choose to make a purchase.You can read my complete affiliate disclosure for more details

Can You Have Both Tank and Tankless Water Heater?

A tankless water heater is a heat exchanger that offers a constant hot water supply. It heats and stores water on demand as it is consumed, rather than storing hot water in a tank. 

Yes! Your tank water heater will be a backup to the tankless unit. The tankless unit is the primary water heater; its pump will feed the hot water to your fixtures. However, when you need to take a shower due to an outage with your tankless system, the full capacity of your tank water heater kicks in. 

Both units boast wiring into a control panel that automatically switches from one unit to the other at set intervals or when you need to keep everything running smoothly.

If you’re currently using a tankless water heater, switching to a tank water heater when the piping reaches the point where it’s difficult to maintain your current setup is a smart move.

However, it’s important to note that you will have to call an electrician or plumber to make the change. 

In some situations that require a larger pipe to be run from your tankless unit to your water heater, this is possible if you need an electrician.

It’s usually the costlier option, but changing the pipe size between your units will save you money in the long run.

How much does it cost to convert to a tankless water heater?

The cost of converting into a tankless water heater varies depending on your location, unit size, installation complexity, and the availability of rebates.

On average, converting your existing water heater costs about $4000 and will take about two days to complete.

Just like a conversion for natural gas, the tankless system requires a new gas line. The cost of installation is usually another $2500-3000.

The total cost to convert an existing water heater into a tankless one is $7000-8000.

But before you leap and pay for the conversion, remember to check the rebates.

Can You Have Both Tank and Tankless Water Heater?

In most states, local home heating agencies provide incentives for converting an existing water heater into a tankless system.

For example, the energy commission offers $500-1000 rebates on tankless systems in most California counties.

Unfortunately, only so many tankless suppliers can offer a good rebate program. Siemens and Rinnai are two exceptions. They both have desirable rebate programs up to $2000 per unit.

The average heating bill of a converted water heater is around $1500. This will be the value of the rebate, along with the conversion installation cost.

Assuming the current heater is worth $1000, you can recover your investment in about 5 years with a fixed rate financing on an adjustable-rate mortgage or amortizing loan.

Is It Worth It To Switch To A Tankless Water Heater?

Yes! Tankless water heater boasts several benefits that make them worth.

Energy EfficientThey use a lot less energy than traditional water heaters. This means they use less energy to heat the same amount of water, leading to significant savings on utility bills.
Saves You SpaceThe air conditioning system in the average home uses between 25-40 gallons of water per day. Water heaters take up much space, while tankless heaters require minimal space.
Longer Life SpanIt boasts a lifespan of around 20 years, compared to 10-15 years for traditional water heaters.
Faster Start-Up TimeIt takes 5-15 minutes to start up, compared to over an hour for traditional water heaters. This means that when you want hot water, it heats up quickly.
Unlimited Hot WaterThey don’t have a limit like traditional water heaters. This allows you to generate as much hot water as you need whenever you need it
Cheaper Installation CostsBecause of the above features, you can install tankless water heaters in a shorter period than traditional water heaters.

Additionally, there are no pipes to install when installing a tankless water heater, making it cheaper than traditional models.

What Size Tankless Water Heater Do I Need for A Family Of 4?

It depends on several factors:

Incoming Water TemperatureIf the incoming water temperature is cooler than 50°F, you need a larger tankless water heater.

For example, if the water temperature is 55°F, you will need a 20-gallon tankless water heater
Cold water DemandIf it is a high-demand time of year, such as winter or summer, with high humidity, you will need to have a larger tankless water heater capacity.

For example, if it is mid-summer and humid outside, your family could use up to 14 gallons per hour combined with cold and hot demands.

In this case, you would need a 40-gallon tankless water heater.
Desired Output TemperatureIf you want to use a showerhead that only accommodates 75°F and higher, you may want to consider a tankless water heater with a lower output temperature.
Flow Rate Required To Meet The Hot Water DemandsIf the hot water demand is high, such as during a vacation, you will need a larger tankless water heater capacity.

For example, if you have guests over for the weekend and there are 6-8 people per shower and one person in the family will be taking a shower at a time, you would need 24 gallons of water per hour.

At this flow rate and temperature setting of 90°F, you would need a 40-gallon tankless water heater.

Common Problems with Tankless Water Heaters? – How To Fix

ProblemExplanationHow to Fix
LeaksLeaks are the most common problem with tankless water heaters.

They occur due to improper installation and can also be due to:

Bad temperature/pressure relief valve seals or faulty anode rods.
Check that the pressure/temperature relief valves are set correctly and sealed properly.

Before installing them in the water heater, make sure to twist the anode rods fully.
Low Flow RateA tankless water heater will produce a higher flow rate with less pressure than a conventional storage-tank water heater.

You can expect a flow rate between 0.5 and 1.5 gallons per minute.
Check with the manufacturer’s manual on the lowest temperature to which the heater can heat water.

Ensure your water pressure is high enough to produce this flow rate; otherwise, you will need a booster pump.

Make sure you have set the temperature correctly;

It may be too cold for your incoming water supply and result in a lower flow rate.
Noisy OperationThe burning of the elements causes water heater noise.

If you notice a rattling or rumbling noise, you likely have sediment in your water supply pipes.
Run your faucets for several minutes to flush out the sediment from your pipes.

Shut off the faucets and let the tank fill.

The sound may go away as soon as the water starts flowing through the pipes again.
Water Temperature Is Too Hot Or Too ColdIf the water coming out of your tankless water heater is either too hot or too cold.

Your unit may not produce enough BTUs to heat the water.
Check with your manufacturer’s manual to see what specific water temperature you should expect from a given unit.

You can adjust the thermostat accordingly if you get excessively hot or cold water.
Freezing In Cold WeatherIf you don’t connect the water supply line properly or if a hose bib is left open.

The water heater will freeze and may cause damage to the unit.
Make sure that all hose bibs are closed or turned off.

Make sure there is no spillage around the base of your water heater.

You should also wrap pipes with a cloth to prevent freezing.

How Many Showers Can a Tankless Water Heater Run?

A tankless water heater can run one or two showers simultaneously, depending on your showerhead flow rate and water usage.

But it’s also possible to use your tankless water heater only for occasional showers and still get plenty of hot water for other household uses like laundry, dishwashing, and cooking.

For example, a typical 80-gallon or 3.8 cubic feet water heater can use 2.6 gallons of hot water per minute at full capacity.

Even using the maximum flow rate, it would take 2 1/2 minutes to run a 75-minute shower and 12 minutes to run a 60-minute shower at full water flow.

When tankless water heaters are installed as part of a hot water storage tank installation, the installer can calculate the flow rate necessary for a particular showerhead.

It is expressed as gallons per minute or hour, depending on the hot water storage tank size.

Water heater flow rates vary by whether the entire hot water system uses one or two loops.

Can You Have Both Tank and Tankless Water Heater?

A single loop is all the hot water from one tankless water heater and a radiator or baseboard hot water system.

A two-loop system uses two separately controlled, small tankless water heaters, one for the shower and bath fixtures and another for the laundry, kitchen, and other household sinks.

Why Do Tankless Water Heaters Burst?

1. Poor Maintenance

A faulty gas valve or improperly installed igniter can cause an overflow of gas and result in a water heater explosion.

If you’re in doubt about your water heater’s safety, contact a professional to inspect it.

2. Defective Design

Sometimes a faulty valve will make it possible for the tankless unit to build up pressure high enough to burst its glass containment vessel, which could go from bursting at the seams to collapsing completely.

3. Improper Installation

For the same reason above, installation becomes critical to the integrity of the tankless unit. If you install it correctly, there is a much higher likelihood of it bursting from excess pressure.

4. Consistency of Water Flow

When your cold water isn’t flowing properly, it can cause an overload on your system that can cause the tankless unit to burst its seams or collapse completely.

The water flow must be consistent for the water heater to function properly and safely.

5. Overloading Your System

Sometimes the tankless water heater needs to be bigger to keep up with the demand of your home. 

6. Water Pressure

If you live in a home with high water pressure, consider a well-known brand name for safety reasons.

In case of any issues with your tankless unit, you should immediately contact a professional and ask them to inspect it for possible damage. 

7. Gas Pressure

As with water pressure, gas pressure can cause an explosion if the unit isn’t installed correctly. 

Tankless Water Heaters: Indoor vs. Outdoor

FactorIndoor Tankless Water HeatersOutdoor Tankless Water Heaters
LocationBoast indoor installationNeed outdoor installation
Power SourceRequire no power or minimal power, like a space heaterRequire direct power from the electrical panel.

Which can draw on the surrounding electricity supply and often generate noise or pollution.
NoiseMake no noise since they are not physically connected to the surrounding elementsRequire power, making them noisy as they need to be physically linked to the surrounding sources of electricity.
InsulationHave limited insulation and require a barrier, such as a plastic covering or insulating case.Do not require such insulation or coverings, which makes them better suited to harsh weather conditions.
AccessibilityMore accessible because you don’t need to connect them to a power source.Can be hard to access and require professional installation.
MaintenanceRequire little maintenance since they don’t need electrical connections.Require more maintenance than indoor tankless water heaters.

Due to their connection with the surrounding elements and their need to be installed by a professional.
CostCost less than outdoor tankless water heaters because of their simplicity and ease of installation.Cost more than indoor tankless water heaters due to their need for power connections and installation process.

Can Tankless Water Heaters Leak Carbon Monoxide?

Yes! Tankless water heaters leak carbon dioxide due to the following:

1. Poor Installation

Poor installation of tankless water heaters can leave gaps where poisonous gases and odorless carbon monoxide can escape.

2. Furnace Malfunction

If your furnace malfunctions, such as element failure or dirty filters, CO can escape from your water heater tank.

3. Improper Maintenance

Gas water heaters must boast proper maintenance to prevent leaks and lack of heat. 

4. Improper Venting

Improper venting can occur when you leave your gas water heater on overnight.

This is especially dangerous if the water heater is not properly vented to the outside and the tankless water heater is located in a garage or basement with poor ventilation.

5. Leakage

The other most common cause of leaks is corrosion at the sending unit.

This can occur either because of lack of maintenance, improper installation, lack of venting, or a water supply that is not hot enough to cause the recommended amount of evaporation required by tankless water heaters.

6. Improper Testing

Most manufacturers recommend an annual test of your water heater to ensure the most dependable operation.

In all fairness, the test should be done, but only once a year, with appropriate care and caution.

7. Failing Water Heater Element

Tankless water heaters fail in the same manner as their hot tank counterparts, but the damage is usually more severe with a tankless water heater.

This is because of their smaller size and the fact that they are designed to run 24 hours per day as opposed to continuous ignition type heaters, which only run for a few minutes an hour, or less.

So, if your igniter or element in your tankless water heater fails, it will almost certainly require the replacement of the entire unit.

Are Tankless Water Heaters Noisy?

Yes! Tankless water heaters will all make some noise when starting up and heating water. The sound is typically around 50 decibels, which feels like someone speaking close to your ear.

This may vary depending on different factors, such as:

1. The Type of Pump Used in The System

Some pumps are noisy, while others are quiet.

2. The Water Temperature

The hotter the water, the noisier they are. If you want to reduce the noise, use a lower setting on your water heater or turn it off completely.

3. The Pressure of The Incoming Water Supply

Noisy tankless water heaters will operate at a lower pressure than quiet ones, but they all need at least 10 PSI to work properly.

Can You Have Both Tank and Tankless Water Heater?

4. The Distance Between the Pump and The Water Heater

The farther away these devices are, the less pumping sound they make. However, the farther you are from the pump, the longer it will take to heat your water before you can use it.

5. The Grade of Your House Foundation

The closer your house is to ground level, the more noise you’ll hear from inside the basement or cellar.


Tankless water heaters are an excellent addition to your home if you need to conserve money on your water heating costs.

You can use them in areas where the water is very hot such as near the ocean or where hot water is necessary for cooling purposes


Hi! I I faced many questions from customers about different products, and there was hardly any help on the internet. After learning all the things about these products as a manager the hard way, I decided to start a blog and help other people.

Recent Posts