Water Heater FAQs

Q: What is efficiency?

A: Efficiency is the amount of energy output as compared to energy input. For example, an 80% efficiency rating indicates that 80% of the heat goes directly into the water, while 20% escapes.

Q: Do tank type heaters continuously run all day to keep water hot and in turn waste energy?

A: Contrary to what you may have heard, tank heaters do not run or heat water all day long. The burner will ignite to provide additional heat only when the temperature of the tank drops below the thermostat set point. In a typical household, the tank type heater will provide all of the hot water needs with a burner firing for less than two hours a day. If no hot water is being used, the burner will probably fire for one or two short burn times in a 24-hour period in order to maintain the tank temperature.

Q: Are tank type heaters less efficient than tankless water heaters?

A: Yes, but not by much –Tankless water heaters are more efficient and have a higher energy factor (EF) since there is no standby heat loss (the loss of heat when stored hot water is not being used). Tankless units can provide an EF around 0.80. tank type water heaters will vary in EF, but range from approximately 0.50 to as high as 0.81, basically matching tankless. Our Hybrid unit, the Vertex, offers 90% thermal efficiency.

Q: Does tankless really deliver endless hot water?

A: This really depends upon the hot water demand. A tankless unit heats the water as there is a demand for hot water. The modulating burner adjusts its intensity to match the demand based on the flow rate. As long as flow rate does not exceed heating capacity, endless hot water will be supplied. However, there are situations where it can not respond as quickly as desired or demand outpaces the unit’s capability, creating a hot water flow rate below the desired level.

Situations such as low volume or steady stream needs and a small number of simultaneous users are the best scenarios for tankless units. For homeowners that may have peak demands with multiple devices, a tank or hybrid water heater is the recommended solution.

Q: Why is a tankless unit so small?

A: Since water flows through the heat exchanger based on flow demand, the unit does not utilize storage capacity. The absence of the storage tank minimizes the physical space required. A tankless unit is typically 13 inches by 24 inches by 9 inches and hangs on a wall. However, most owner’s manuals for tankless water heaters suggest the installation of a drip pan on the floor beneath the heater, which limits use of this space. Many tankless units can be installed outdoors, which can be a real advantage for space savings but it should be noted that in cooler climates additional energy will be used to prevent the tank from freezing.

As a consequence of small size and on-demand water heating, the heating elements and gas requirements for tankless water heaters are normally much larger than those for tank type water heaters. On average, tank type water heaters have a gas input of 40,000 Btu/h, while tankless water heaters can go up to 200,000 Btu/h. Similarly, electric tank type water heaters draw up to 6,000 watts, but electric tankless heaters can draw as much as 28,000 watts. While a tankless unit may save you space, it will frequently require larger gas lines and vents or a higher capacity power supply.

Q: Is it true that tankless water heaters never leak?

A: It is common to assume that the absence of a storage tank reduces the potential to leak, but the tankless unit’s internal water flow tubing can be damaged or deteriorate, causing a water leak and significant water damage. Most tankless unit manufacturers suggest the installation of a drip pan under the unit.

Q: What is a “cold water sandwich?”

A: More common to tankless water heaters than tank type, a cold water sandwich results from when several “off” and “on” water operations (such as back-to-back showers or washing dishes) create large slugs of cold water between hot water in the piping of a home. Commonly, the piping behind the walls loses heat slower than piping in a crawl space or basement. If there is hot water drawn and then the flow is stopped for a short period of time, the water in the most exposed piping cools off faster than other areas. If someone opens a fixture at the right time, the first water out of the tap is hot, then goes cooler as the water from the exposed piping gets to the fixture. The water from the fixture will heat back up again when water from the heater finally arrives. This situation creates the cold water sandwich.

In some homes, a tankless water heater can exaggerate this effect. Here’s how the process works:

When the demand flow stops, a tankless water heater stops firing and the draft fan continues to run as a “post purge” to ensure that all exhaust is moved out of the venting system. It runs for about one minute and during this time it cools off the heat exchanger. Usually, the heat exchanger holds a little less than a quart. When the tankless water heater senses flow demand again, it fires back to provide hot water for the next draw. The water in the piping may still be hot, but the initial flow of water to leave the heat exchanger is not. It does take about 1-2 seconds for the tankless water heater to get going. When the first quart of water enters the pipe with the water that is still hot from the last draw, the different water temperatures merge as it flows down the line. Eventually, the lower temperature water gets to the user and they notice the temperature fluctuation.

Q: Is tankless for everyone?

A: There are several decision factors regarding what is best for your home. Tankless is a great choice for limited usage situations or in steady stream demand. Consideration for usage patterns, multiple hot water needs, ground water temperature, product price, installation costs and other factors will determine which type of water heater is best for your home.

Since there is a delay in how long it takes for a tankless water heater to produce hot water due to the ignition sequence and the heating of the heat exchanger, there is a 15 second delay for each draw of water. An average household has 40 to 60 draws per day, so this delay could translate to a significant amount of wasted water. So, while a tankless water heater may use less energy than some tank type water heaters, they may waste a large amount of water as a result. In many cases, the energy savings are cancelled out due to wasted water cost.

In most of the U.S., the average homeowner will save less than $75 per year by having a tankless water heater over a tank type water heater once unit costs, installation costs, energy usage costs and water costs have been calculated.

Q: What is heavy peak usage, and which unit is best for this?

A: Most American homes follow the usage pattern of heavy demand for multiple showers or baths during a 60-90 minute period in the morning, followed by another high demand period in the evening with washing dishes, clothes and nighttime showers. A tank type or hybrid unit is best suited for this type of usage pattern because of their ability to deliver a large volume of stored water.

Q: How do I properly maintain a tank type water heater?

A: It is recommended that the tank type water heater is drained annually to minimize the buildup of sediment in the bottom of the tank, as well as have a general inspection or tune-up by a licensed professional.

By comparison, the inlet filter in tankless water heaters should be cleaned on a monthly basis and the unit should be flushed regularly with a glycol solution. The tankless heaters should also be serviced annually by a trained technician.