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Content Type:Q&A

Question:

Do you have energy conservation tips for hot tubs?

Answer:

Your hot tub is not unlike your home's water heater: a large vessel of water that you keep hot for the times you'd like to use it. Unlike your water heater, however, you don't use the hot tub as much as you use domestic hot water, so you may not need to heat it 24 hours per day.

If you're like many hot tub owners, you really only use the tub (at most) once or twice a day, and generally at pretty routine hours—often in the morning and then again after dinner or just before bedtime. Whatever your usage patterns, you probably have a pretty good idea of the typical hours you use your tub. That's when you want the tub at your desired temperature. One way to reduce your hot tub operating costs is to only heat it during the periods when you'll actually be using it. Setting the heater timer to come on and heat the tub 15-20 minutes before you'll actually be using it, and turning the heaters off after you're finished will ensure your lowest operating costs. If you find that the tub isn't up to the desired temperature when you get in, you can adjust the timers to come on a little earlier.

Some electric utilities offer "off-peak" rates—times of day when the cost of electricity is lower. If your utility offers this rate, you may want to consider operating the tub heater during those times.   

Your monthly hot tub operating costs are determined by how often and for how long the heater has to run to maintain the desired temperature. There are several factors that affect this: the location of the tub, age and insulation level of the tub, and the kind of fuel used to heat the tub.

If your hot tub is located inside the house, or in an enclosed area outside, the tub will lose less heat to the environment, and therefore cost less to heat.  If it's outside, poorly insulated, or not well shielded from the wind, it may cost considerably more to heat. If your tub is located outside, and in a particularly windy spot, consider adding a wind/privacy screen. Not only will this screen reduce the heat loss from the tub caused by exposure to the wind, but it may also increase your comfort while getting into and out of the tub.

Today's modern hot tubs are better insulated than their predecessors. Depending on the age of your tub, the insulation can range from a thin layer of foam under the tub shell, all the way up to a fully-foamed cabinet. A well-insulated tub will maintain its temperature longer with less supplemental heat required.

The hot tub's insulated cover is the most important component to reduce heat loss in the tub. When the cover is removed, the heat loss from the surface of the water is several times the heat loss from the tub itself. A cover that does not provide a good seal to trap water vapor will waste energy, water and chemicals. One way to determine if your tub's cover is tight is to use your nose. If you can smell chemicals with the cover in place, the cover is leaking and should be repaired or replaced.

The condition of the hot tub's insulated cover will also have an impact on the cost of operation. If the insulated cover is over five years old, you may want to think about replacing it. Over time, the foam insulation in the cover absorbs water. That's why the cover gets heavier as it ages. Once the cover becomes water logged, it loses a lot of insulation value and doesn't work as well to stop heat loss out the top of the hot tub. Replacing the cover with a new dry cover will lower your monthly operating costs.

Purchasing A New Tub?

If you are purchasing a new hot tub, start by buying the best cover available—one with good seals and lots of insulation that does not absorb water. In choosing the hot tub, look for units with lots of insulation - the more the better. Also consider a unit with separate filter and bubbler pumps; many units use a single two-speed pump that runs continuously at low speed (and low efficiency) to filter the water, switching to high speed when the bubbler is activated. Finally, buy the smallest tub you can—small is beautiful, and it saves energy. While it's nice to invite all your friends over for a dip, that is pretty rare and most of the time the spa is used by not more than two or three people at a time.

Additional Resources

Hot Tub and Pool Conservation Tips (121K Adobe® Acrobat® .pdf), Washington State University Extension Energy Program, 2003.

Heating & Dehumidification Costs Due to Evaporation from Swimming Pools, Washington State University Extension Energy Program. This downloadable spreadsheet was developed by a WSU Energy Program engineer to calculate energy loss for pools using the "Shah" method. The spreadsheet calculates energy use and takes into account activity level, air and water properties, dehumidifier energy, etc.

Topic: Building/Space Type--Sports/Recreation
Topic: Water Heating--Conservation
Topic: Water Heating--General
Topic: Water Heating--Insulation
Sector: Residential
Sector: Commercial
Content Type: Q&A
Keywords: hot water, spa, spas
ID:  2290