Keeping the Hot Tub Hot

This fall I wrote about our insulation woes and our high electric bill.  Although we built storm windows,

“…our electric bill did not go down appreciably. But that is another story…”

This is that other story.

We have lived in this wee house now for 3 years.  Home sweet home.  Practically, this means I now have records for three complete years of electricity use.  Electricity powers everything in our house (except our solar phone chargers!), so not surprisingly, we use more electricity in the winter than summer – twice as much.

I suspected that the hot tub contributed considerably to our electric bill.  The three-year record clearly shows how much the hot tub adds.

In 2009, the heating element burned out.  Twice.  In a row.  It was off-line for most of the summer. It burned out again in Jan-Dec 2011.  Although the timing does not perfectly coincide with our electric bill cycle, it gives us a good idea of how much the hot tub contributes (see graph below).  And the answer is – a lot.

The hot tub accounts for 50% of our winter electricity use and approximately 70% of our summer use.

Discrepancies are periods when the hot tub was offline

Discrepancies among 2009-2011 are periods when the hot tub was offline

Here are the reasons our hot tub is so wasteful:

  • it’s a hot tub; even the most efficient are wasteful
  • wood-barrel instead of high tech synthetic plastics and insulating foams
  • to heat, water leaves the hot tub on exposed plastic pipes, travels up to 4′ to an uninsulated ‘dog-house’ pump station, and returns along other exposed plastic pipes
  • hot tub lid was old, and cracked, and grew moss; clearly heat and moisture were escaping

The original hot tub cover showing crack, gap, and moss.

Many of these offenses are easy to fix, such as insulating pipes and the pump house (OK, I still have not finished that project). We also put the hot tub on a schedule; instead of heating 24-7, it now runs for two 4-hr periods, losing about 5-degrees F in the intervening 8 hours. Not sure whether or not that is better.

Finally, we got a new hot tub cover.

Spa Cap floating on the hot tub surface and draped over the lip.

Spa Caps are custom-made in Lynden, WA by real people. Real people you can order from after talking with them on the phone. Seriously. As the Spa Cap website will tell you, they had this great idea to insulate hot tubs with air, instead of foam that tends to saturate and need replacement within 10 years. There are no less than three air baffles in my spa cap. Because the spa cap floats on the water, there is less opportunity for evaporation because heat is not lost to the air layer between the water and the hot tub cover. Nifty.

Despite below-normal temperatures during Dec-Jan 2012, we actually saved electricity compared with previous Dec-Jan periods when the hot tub was working (2009, 2010). We used 23% less kWh than 2010 and 33% less than 2009. Not a lot else changed in the house, so I tentatively call the Spa Cap a success.

We would never have bought a hot tub, but because it was here when we moved in we felt we had to try it. And we love it. Great for warming up on a chilly morning. To relive sore muscles. And to relax after a long, stressful day of work. It is a luxury – one that we will keep working to improve upon.

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3 Responses to Keeping the Hot Tub Hot

  1. You are such a dorky graph person 🙂

  2. I have read this post and if I could I wish to suggest you few interesting things or advice.

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