To replace a 50-gallon tank water heater, you generally need a tankless unit that produces 8 to 10 gallons per minute (GPM). Unlike tank heaters, tankless models are sized by peak water demand and temperature rise, not storage capacity.
To replace a 50-gallon tank water heater, choose a gas unit with a 6.5 to 9.8 GPM (Gallons Per Minute) flow rate or an electric unit drawing ≥27is greater than or equal to 27≥27 kW. This upgrade provides endless hot water and lowers energy use, though gas units require venting.
For a 3-bathroom home, you generally need a tankless water heater with a flow rate of 7 to 9 GPM (Gallons Per Minute). This size can effectively run 2 to 3 major hot water fixtures (such as a shower and a washing machine) simultaneously.
A 50-gallon water heater typically supports 3 to 4 people with standard showering habits. You can generally get 4 to 5 consecutive showers (lasting about 10-15 minutes each) before running out of hot water, though this heavily depends on your showerhead flow rate and whether it is a gas or electric model.
Tankless water heater installation costs between $1,404 and $3,899 for your home, depending on unit size and setup. The fuel type you choose shapes your upfront and utility costs, with electric lower-priced and solar earning tax credits.
For a family of 5, a 50-gallon water heater can work, but it will be tight and requires careful scheduling. You will likely experience hot water shortages if multiple people take back-to-back showers or run appliances like the dishwasher and washing machine simultaneously.
Plumbers often hesitate to recommend tankless water heaters because they act like high-performance sports cars. Unlike traditional tank models that are "workhorses" and can function while mostly ignored, tankless units require precise installation, regular maintenance, and are highly sensitive to mineral buildup.
For larger households, multiple showers, laundry, and dishwashing may run at the same time. Hot water demand could reach 10–12+ GPM. A high-capacity tankless water heater—or even two units installed in parallel—may be the best solution.
A gas tankless water heater (natural gas) is only marginally cheaper to operate than an electric tankless water heater due to the exceptionally high thermal efficiencies of the electric units (99%+).
Drawbacks of Tankless Water Heaters
As discussed above, the biggest downside of owning a tankless water heater is its higher cost. The initial installation and unit costs are more expensive than a traditional storage-tank water heater.
Here is a simple way to decide: Choose Navien if you want the highest efficiency, longest warranty, and built-in recirculation. Choose Rinnai if you have a large household and need the highest flow rates. Choose Rheem if you want a reliable brand at a lower price point.
A water heater that is too small will struggle to keep up with your household's demand, resulting in inconsistent hot water. Conversely, a tankless water heater that is too large may waste energy and cost more than necessary.
In freezing temperatures, condensate produced by a condensing tankless hot water heater can freeze inside the drain line, which can cause leakage, operation issues or shutoff. To help keep your indoor tankless water heater from freezing, use a direct vent exhaust & intake system.
You can see that, in a typical gas system, a tankless water heater with a capacity of 199,900 BTU will require a 1-inch pipe size for a 20 ft branch length (based on the 0.3 in w.c. pressure drop in Table 2). The same appliance would require just a ½” pipe size based on Table 4 the 3.0 in w.c. pressure drop.
Yes, a tankless water heater can fill a bathtub. Because tankless systems heat water on demand, they provide a continuous stream of hot water, which prevents you from running out halfway through filling a large soaking tub.
If a standard showerhead is fitted, it will use around an extra half a gallon each minute, accounting for a 25-gallon emittance every 10 minutes, or 50 gallons throughout a 20-minute shower. *1 gallon = 4.54 litres.
A tankless water heater usually goes cold mid-shower because the water flow drops below the heater's minimum activation threshold, or the system is overloaded by using too many fixtures at once. It can also happen if sediment blocks the filter or the unit is improperly sized.
Here are some common reasons why your tankless water heater might not be working and how you can troubleshoot these problems.
This problem usually comes down to capacity, heat production, or mixing issues inside your plumbing system. Sometimes the fix is simple, like adjusting your water heater temperature or flushing out sediment. Other times you may need a new mixing valve, an element replacement, or a different size water heater.
The answer is no — tankless water heaters can save money on your monthly electric bill because they're 8%-34% more efficient than storage water heaters.
A 10-minute shower typically uses 12 to 25 gallons (45 to 95 liters) of hot water. The exact amount depends on your showerhead's flow rate and the temperature you prefer (as hot water is mixed with cold):