Tankless Water Heating is getting a lot of notice these days as many people are seeing more advertising for them. The pro’s given are many along the lines of it will save you money because you are only heating what you are using and don’t have to maintain a tank full of water at temperature, you will never run out of hot water, the tankless water heater is small, or the tankless water heater lasts longer than a tank type water heater just to say a few of them. Are they true? Sort of. Is tankless water heating for me? Maybe. Really the best answer is to look at your needs and determine what tankless has to offer compared to a tank type water heater and see which best meets your needs. Energy Star figures show that a family of 4 will save about $175 per year so the pay back is well over 10 years away and probably is not worth considering heavily.
Lets first look at how a tank type water heater works. The residential tank water heater is typically 40 – 80 gallons in size and about 70% of the water in the tank can be used before the incoming cold water mixes with the stored hot water and a temperature difference becomes noticeable. The water is stored and ready for use so reheating is not required to be instant and the water is typically heated by a 4500 watt electric element, or 40,000 Btu burner. An electric water heater might recover 20 gallons of hot water an hour if it had to heat it 90 degrees, or a gas water heater might do 30 or, 40 gallons per hour under the same conditions. Basically we are saying the tanks heat slow and store a large quantity so you have enough.
Now lets look at tankless water heaters and how they operate. With tankless water is not stored hot. When you turn on a hot faucet and the flow meets the minimum flow requirement of the flow sensor for the tankless water heater the unit will turn on and start heating water. The minimum flow varies with different manufacturers and models. The tankless unit is required to instantly heat the water you are using so a large burner is used with a burner that modulates adjusting the burner flame to the size you need for the amount of water you are flowing. This burner may modulate from 10,000 Btu to 199,000 Btu in residential units. Electric tankless water heaters require high amperage power supplies as high as 160 amps for some. Once the water stops flowing the heating cuts off until the next time the sensor activates from water flowing.
Lets examine some of the differences and implications between tank and tankless water heating.
The difference in energy consumption rates: The amount of energy needed to raise the temperature of a gallon of water from 50 to 120 Degrees F is the same whether it is done fast or slow. However, use of a tankless requires large amounts of energy available for the instant heating. Your gas or, electric service may require upgrading to supply the energy the tankless requires. The 199,000 Btu vs. 40,000 Btu burner or 160 amperes vs. 30 amperes are significant differences in demand. The added cost of a service upgrade if needed could be significant.
Temperature rise and how it affects water heating: With a tank water heater the speed at which the tank recovers is longer with colder incoming water supplies. The burner flame or electric heating element doesn’t change even though the heating requirements do. This is part of the tank sizing where the tank is sized large enough that you don’t run out even after using some of the water and needing more while it is recovering. With tankless water heating you are limited by how much the water being used can be heated by a given burner size. In warm areas with higher incoming water temperatures this will not be as significant as an area where winter water temperatures may be 35 Degrees F. Years ago the manufacturers were calling this specification “Rate of Rise” now they are referring to it as “Delta T.” In the specifications for the tankless unit you are considering showing the maximum flow that can be heated to 120 Degrees F from various incoming water temperatures. A tankless heater may supply 120-degree water at 6.3 gallons per minute up to a 40-degree Delta T. A 60-degree Delta T might provide 4 gallons per minute. An 85-degree Delta T might provide 2.8 gallons per minute of 120 Degree F water. So while a tankless water heater will never run out of hot water the tankless does have limitations in how much volume it can produce especially with colder incoming water temperatures. The tankless unit or units in some cases have to be sized to meet the demands of your water usage even at the coldest incoming water temperatures of the year.
Standby heat loss: Many people place a high value on the stand by heat loss of a tank type water heater in comparison to a tankless heater not storing heated water. In the case of today’s well-insulated electric water heaters the standby heat loss is fairly low and slightly higher in gas water heaters with the flue running up through the center of the tank. Standby loss is typically somewhere in the range of 25 to 50 cents per day.
Space is a good reason to consider tankless water heaters. Interior tankless units can fit in a closet on a wall and in warmer climates exterior tankless units can be mounted on an outside wall. Tankless uses far less space than a tank type water heater.
Tank type water heaters have a service life of about 12 years while tankless water heaters are expected to last 20 years. Neither water heater is maintenance free however. Minerals are present in water (hardness) and when water is heated the minerals precipitate out of the water. Tank water heaters should be flushed at least once per year to remove the lime deposits from the bottom of the tank. A severe build up in a tank water heater can cause the lower element in an electric water heater to burn out and in a gas water heater insulate the water from the burner. In a tankless water heater the tankless coil can become clogged with lime and the de-liming service is recommended every year or in extremely hard water conditions more often.
I hesitate to offer price differences because they vary widely across the country but a good estimate to install a tankless vs. a tank type water heater is probably 2½ times higher to put in a tankless over a tank type. There are a lot of variables and the only way to be sure is getting quotes and comparing. I would not recommend a DIYer installing a tankless water heater as they are very complex and many things have to be considered to have a satisfactory installation.
Hopefully this helps you understand Tankless Water Heating and will have you asking the right questions about tankless so that you understand the decision you are making. Only you can answer the question if tankless is right for you.