I was thinking about what topic to post this weekend and got a call from my sister. She asked; Where can I get a tankless water heater? This was fortuitous, because I had just read an article about gas tankless water heaters and the comparative costs of installing one versus a standard gas water heater. In that article the comparison was not very favorable. Because you want to know? Well, it looks like she’s renovating her laundry room and wanted to reclaim the space in the corner that her standard water heater takes up. So I did some quick research.
My sister doesn’t have gas service, so I researched the electric tankless heaters available. Now, a couple of things to think about very carefully when it comes to tankless water heaters, especially electric ones, is her family’s lifestyle. If you have 4 teenagers and 2 working adults, you may pay more to heat your water with a smaller tank heater than if you have a standard water heater.
This is especially true if you live in colder climates or if your water comes from a deep well. In these cases, the incoming water will be colder than if you live in Florida or Texas, so you will need to increase the water temperature more than if you lived in Florida (average tap water temperature is about 70 degrees in the winter, in colder climates, the water is only 40 degrees from the tap). Since teens take longer showers, the savings may not be there.
General physics will tell you that it takes 1000 watts to raise 4.1 gallons of water 100 degrees. Based on this, if you are importing water at 40 degrees, it will take 10,000 watts to raise 40 gallons (typical size of a standard water heater) of water to a standard storage temperature of 140 degrees. Now once it rises it will start to cool down, albeit slowly with the improved insulation on newer water heaters.
At a KWh price of 10 cents, the cost to heat that water was $1.00. Now compare that to an electric tankless unit that produces a 65 degree temperature rise at 2 gallons per minute (suitable in Florida with a 65 degree inlet temp, not suitable in New York or Maine). This particular unit is rated at 14KW. That means that while it’s heating up it’s going to burn 14,000 watts of electricity per hour. That same 40 gallons will take 26 minutes to heat up and will cost about 60 cents. Sounds like a big savings, right?
Well not exactly. You see, when your standard tank is full, it reduces the energy needed to heat the incoming water, since the incoming water will absorb some of the heat from the already hot water, reducing the input a bit to raise the temperature of the water. In a tankless tank there is no stored hot water, so the electricity required to heat the water is expended in a direct proportion. In tests, the range of savings when comparing tankless to standard water heaters has fallen into the range of 10 to 40 percent (higher ranges are found on gas-fired devices).
So the next consideration is the cost of installation. In this regard, you will spend about $1,200.00 in labor and equipment to install an electric tankless heater, as long as you have enough capacity in your electrical panel. Assuming yes, we compare this cost to an approximate installed cost of $600.00 for a standard electric water heater. Furthermore, the expected savings are therefore, according to government research:
For homes that use 41 gallons or less of hot water per day, demand water heaters can be 24% to 34% more energy efficient than conventional storage tank water heaters. They can be 8% to 14% more energy efficient for homes that use a lot of hot water, about 86 gallons per day. You can achieve even greater energy savings of 27% and 50% by installing a demand water heater at each hot water outlet.
Source: http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=12820
So let’s break this down. If you have 4 teenagers in the house you probably use more like 120 gallons of hot water per day so your savings will be gone unless you can afford to install 3 units (costs about $3,600.00) to cover both the bathrooms and kitchen and the clothes. Washed. Even then, your savings will be between 27% and 50% of your water heating cost.
Government figures now say the average electricity bill allocates about 13 per cent to heating water, so if your monthly bill is about $100.00, your savings could be 3-6.00 per month. Also, taking a shower and doing the dishes or laundry at the same time will likely expand the capabilities of the electric tankless heater I’m using in the example, so you’ll need one or the other larger and a larger electric service unit. your installed cost will increase dramatically. So the savings just aren’t there.
If, on the other hand, there are only 2 of you and your lifestyle easily adjusts to accommodate the demand between showers, dishwashing and laundry, then you may be able to achieve some savings by installing the tankless heater. At this point, given the numbers, I couldn’t see any justification in my family. There is another factor to consider, tankless heaters have a life expectancy of 14 to 18 years, a standard water heater will last 6 to 12 years depending on the hardness of the water and the maintenance that is done on it. So I had to tell my sister about the fact that the tankless installation will cost more, it will save them a minimal amount in operating costs, but it would save her the 7 square feet of space that the current water heater takes up in the utility room. In the end, she will have to decide if it’s worth it.
