Tankless-Water-Heaters & Making the Right Choice


Tankless-water-heaters heat water directly with no need for a storage tank. Because of this, they do not suffer from the heat loss that all traditional water heaters suffer from and are considerably more efficient than a conventional hot water tank.

When the hot water is turned on, low temperature water moves through the pipes and into the water-heater, where it is quickly heated. As a result of this efficient design, tankless-water-heaters can deliver a steady supply of hot water.

Rinnai 75iN Natural Gas 7.5 GPM Tankless-Water-Heater

There is never any need to wait for the water storage tank to fill up before you can use your hot water. Tankless-water-heaters supply hot

water at an average rate of 3.5 gallons per minute, and as high as 9.5 gallons per minute. They are also ideal for outside tasks like pool houses and as solar heating boosters.

Benefits of Tankless-Water-Heaters

  • Small compact design uses less square footage
  • Up to 33% more efficient than a conventional hot water tank
  • Only activates when there is hot water demand
  • Saves considerable energy
  • Differentiates your home from others
  • Eco-Friendly
  • Rebates are typically available, product manufacturer, Federal, State, Local utility company
  • NEVER run out of hot water
  • Scalding protection

How Tankless-Water-Heaters Work

Electric Tankless-Water-Heaters

Every electric water-heater design will have its own electrical requirements. You will need to be sure that your home can support the electrical needs of your electric tankless-water-heater before you purchase and install it. It may be necessary to put it on its own circuit. You should consult with a licensed electrician for more detailed information. Use our "Find Local Pros" box at the end of this article.

Gas Tankless-Water-Heaters

The typical gas-fired water-heater will create higher hot water flow rates than the typical electric water-heater can. If your home runs on gas heat, you will need to do a few things. First, figure out the kind of gas that your system uses, natural gas, or propane. Second, it is critical that you get a professional to check your home's gas lines to make sure that they will meet the needs of your new gas-fired tankless heater. Third, you will have to consider the system's venting needs. Check your local building codes to be sure that your home meets all of the requirements--see the "Find Local Pros" box at the end of this article to find someone qualified in your area.

Sizing Your Water-Heater

When looking for a tankless-water-heater, you will also have to consider where you are going to use the hot water. Are you looking for a unit that will heat the water for one sink? If so, the smallest models will do. If you want to heat water for all of your bathrooms and kitchen then you need a larger model, suitable for multi-point use.

The smallest tankless heaters are not able to heat enough water at once for the simultaneous use of a lot of different appliances. If you want to heat water for an entire house, get a model large enough to satisfy your total home's GPM at peak demand AND raise the inlet temperature of the incoming water appropriately.

Calculating the PEAK Demand Flow Rate

The peak demand flow rate is the rate at which you demand hot water to flow when you use your water consuming devices at the busiest time of day. Knowing the peak demand flow rate for your home is critical, as a properly sized water-heater will create a temperature rise that is proportional to your peak demand flow rate. You need a water-heater that can handle the demand flow rate of all of the appliances that will be used simultaneously.

This part of the calculation is pretty straightforward; just consult the gallon per minute (gpm) chart below, add up all of the gpms that you want the unit to cover during the busiest time of day, and this represents the total GPM requirements for your home. Next you need to check the water heater that you're considering and be sure it can supply your total GPM requirements based on your inlet water temperature. As a rule of thumb, use 40 degree inlet water temperatures for northern climates, and 50 degree inlet water temperatures for those states that are considered in the sun belt.

Shower: 2 1/2 gpm 

Bathtub: 3 gpm

Bathroom sink: 1/2 gpm 

Kitchen sink: 1 gpm

Dishwasher: 2 gpm

Washing Machine: 2 gpm

Multihead showers: Consult the manufacturer's specifications

You can get a decent idea of what kind of system you need just by performing a simple analysis of your home's hot water needs and capacities. Once you have a rough idea, call in a professional for an in-depth consultation. He or she will be able to fill you in on anything you might need to know, and help you find installation assistance, if you need it.

For various safety reasons, installing a tankless-water-heater is NOT a good DIY project. Your new water-heater needs to be installed by a plumbing professional as these units have venting requirements, water pressure requirements, and natural gas or electrical consumption requirements. Use the free handy "Find Local Pros" box to the left of this paragraph to find a well screened professional to get the job done right.

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