I was thinking about what topic to post this weekend and I 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 favourable. 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 occupies. So I did some quick research.
My sister doesn’t have gas service so I researched available tankless electric heaters. 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 teens and 2 working adults, you may pay more to heat your water with a less hot tank than if you have a standard hot water heater.
This is especially true if you live in colder climates or if your water comes from a deep well. In these cases, your incoming water will be colder than if you live in, say, Florida or Texas, so you’ll need to increase your water temperature more than if you lived in Florida (average tap water temperature is about 70 degrees in 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 40 degree water, 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 in 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 producing a 65 degree heat rise at 2 gallons per minute (suitable in Florida with 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. Those same 40 gallons will take 26 minutes to heat up and cost about 60 cents. Sounds like a great 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 spent in direct proportion. In tests, the range of savings when comparing tankless to standard water heaters has fallen in the 10 to 40 percent range (higher ranges are found in gas-fired devices).
So the next consideration is the cost of installation. In this regard, you will spend around $1,200.00 in labor and equipment to install a tankless electric 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. In addition, 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, around 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 clothes. Washed. Even then, your savings will be between 27% and 50% of your water heating cost.
Government figures now say that the average electricity bill allocates around 13 percent to heat water, so if your monthly bill is about $100.00, your savings could be anywhere from 3 to 6.00 per month. Also, taking a shower and doing 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 a larger one or the other 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 can 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. So I had to tell my sister 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 hot water heater takes up in the utility room. In the end, she will have to decide if it’s worth it.