Posted in clean renewable energy, decarbonization, electrify everything, energy efficiency, pipelines, water heating

Getting into hot water

As we gutted a Philadelphia row home, we also planned for it to become a frack-free house. This translates to: No gas appliances delivering fracked gas from Western Pennsylvania into our home. Everything that once used gas would be replaced with electric options.

So far, we’ve happily removed the gas oven / range and the associated gas pipes out of the kitchen. For cooking, we’ve picked out an electric stove. And already own other electric appliances to supplement this: toaster oven, microwave, induction cooktop and crockpot.

But hot water? As with most homes in our city, ours had a tank of hot water, kept piping hot using the fracked gas pipeline coming right into our basement. It didn’t make sense to have gallons of hot water waiting for us, night and day. As I explained to my nephew, it’s like having a tea kettle ready 24 hours a day, for whenever we might want our 2 cups of tea.

So we began looking at on-demand hot water systems, also known as tankless hot water systems. There are gas models available, but of course, we only considered the electric models. All tankless models are certainly more efficient since there’s no energy loss during storage, but the recurring question seemed to be…

Could the on-demand water heater keep up with our demand?

We learned that the average ground water temperature in Pennsylvania ranges between 45 and 50 degrees F. And that we like our showers at 112 degrees F in the winter, cooler in the summer. This means the water needed to be heated 67 degrees (112 – 45).

We also learned that 1 kW of electricity can raise the water temperature by 7 degrees F at a rate of 1 gallon per minute (gpm). This translates to needing 9.5 kW (67 /7) for a 1 gpm flow.

The average faucet flow is 2 gpm. The efficient shower head we’ve installed at every home we’ve been in for the past 30+ years has a flow of 1.5 gpm. We agreed that we both kept it at mid-flow, rarely at the full flow of 1.5 gpm. And so decided that our demand (in the shower stall) could be rounded down to 1 gpm.

The tankless system we decided on is the EcoSmart 11, suitable for 1 shower at a rate of 1.5 gpm for incoming water at 47 degrees F, ideal for our one bathroom apartment! We also agreed that we could coordinate sink and laundry use based on shower use. The shower use would take precedence.  If this proved inadequate, our alternate plan was to install a point-of-use model under the kitchen sink. The clothes washer we had selected could heat water on it’s own, if needed.

We’ve used this water heater daily for over 16 months and have no regrets. The installation is in the basement, just beneath the bathroom, about the shortest run for the hot water.

How much electricity used during a shower?

We concurred that most of our showers lasted about 10 minutes, or 0.16 hour (10/60).

Per the specs, the tankless system we decided on was rated for 54A and 220 V, or 11,880 W (54 x 220).

For the 10 minute shower, the electricity used would be 2 kWh (11,880 W x 0.16 hour / 1000), about 26 cents at our current utility rate.

The newer packaging now has a yellow EnergyGuide sticker, showing that it uses about 622 kWh annually. I’m reminded of the electric water heater at another house we lived in. It had a 40 gallon tank and used about 4700 kWh annually, over 7 times as much! Talk about an efficient way to get into hot water, with more space in the basement…


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