Heater Size - Kwh Usage - Energy Efficiency

[Itchy and Scratchy]

I have had my 180 gal Marquis Spirit 110 v for 6 weeks now. I use it an hour a day and love it. In an effort to save energy I don't use jets while soaking. I also leave a 1/4 inch foam floating blanket covering 80 % of the tub while I soak. Still this tiny tub with a frugal soaker in it uses 10 KWH a day. This doesn't seem right to me. The tub is 6 years old, looks to be in great shape. I just had a tech out from the local Marquis dealer to check out the heating system, he said all was good. This 300 KWH adds $100 to my electric bill in California 0.40 top tier rate.

Does this kind of electrical consumption sound normal to you? 10 KWH for 180 gallons where are the btu's going?

Here is the math.

1 KWH = 3425 btu's

1 btu to raise 1 lb h2o 1 deg.

Round my tub off at 1500 lbs h2o

34,250 btu's should be sufficient for 23 deg of heat recovery. I have unplugged my tub for 24 hours and it droped from 104 to 96 over 24 hours. 8 deg heat lose over 24 hours would be considered a well insulated tub right???

I am estimateing the 10 KWH a day from comparisons from smart meter billing and the heating cylcles of the tub. There is no economy mode for the controll panel so at the end of my nightly soak I will unplug the tub. I have my wife plug it back in around noon and the heater will run about 6 hours to bring the temp to 104.

This slow heating rate of 1.5 deg an hour was why I called the service tech out. 1.5 KWH heater I have according to the above formula would heat my tub at 3.5 deg an hour. With the 1.5 deg heating recovery rate I can't keep the water up to temp without the thermal blanket.

With my frugal usage of this 180 gal tub I would think 5 KWH a day would be more in line with usage. Is there some thing the service tech missed that could explain this power draw. To me it looks like the tub is calling for power but it is not being put into the water in the form of heat.

I know there are hundreds of years of combined tech experience on this forum. You guys got my water chemistry straight. Can you help me out with this???

[spawn]

Itchy - Your energy use does seem high for that tub. At this point how much energy the tub is using is conjecture. Since you are apparently using 110/120 V power by plugging into a receptacle you could get a better idea of your usage by installing this cheap device, the Kill A Watt Electricity Usage Monitor available at Amazon for 21.79 with free shipping:

http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU

Other thoughts - you must really like the water hot because most tubbers keep the temp around 102. Obviously if you really like the 104 temp, as some do, that is where you should keep it, but it will use more energy. Is the cover in good condition and sealling well? Instead of unplugging the tub when you get out, maybe you could just lower the heat setting to 90 or whatever, so the heater doesn't come on as you desire but the filter cycles will still run. As for jetting, in that little tub (single motor) the jets shouldn't add a huge amount to your bill - it is heating that places most demand. I hate to think of you not using jets because I don't think the cost would be that great, maybe you could use them just 10-20 minutes like some people. On the other hand, just sitting in the still hot water can be very nice.

[Itchy and Scratchy]

Thanks for the kill a watt suggestion. I was planning to get one to see how different heating/filtration cycles affect cost. It won't solve the problem of gross electrical consumption but it will clearly define how much energy is being consumed. Hopefully I can get a tech suggestion about possible problems that could drain power from the tub.

[ChaiSTi]

I estimate that your spa should pull about 12A when it's heating. Do you have a amp clamp to check this? Also, are you sure you have a 1.5 kW heater? 120V spas are usually equipped with 1 kW heaters.

[Itchy and Scratchy]

Yes the heater is 1.5 kWh @ 110 or I can convert to 220 and the heater will put out 4 kWh. The 220 conversion will supply faster heating rate but I feel there is something that is amiss with the electrical/heating component of this tub. It will get to 104 and I can keep it above 103 over an hour long soak with the heater and thermal blanket on. I just seems to me that it is drawing twice the power it should. For a 180 gal tub I feel 150 kWh a month would be more in line, not the 300 kWh I estimate I am using. A kill a watt is one the way and will let me know exactly how many Kwh the tub is using. I will post that update.

Please if anybody has experienced a problem like this let me know.

[ChaiSTi]

4 kW heaters used in 110V system will reduce the wattage about 75% which would make it 1 kW. Unless Maquis is using a special heater, I think you should base your math around 1 kW versus the 1.5 kW that they may claim.

[Itchy and Scratchy]

4 kW heaters used in 110V system will reduce the wattage about 75% which would make it 1 kW. Unless Maquis is using a special heater, I think you should base your math around 1 kW versus the 1.5 kW that they may claim.

That would help bring the heating rate more inline with what I am experiencing. Hopefully the kill a watt is in next week. That will bring light on the situation. A 220 v line will cost over $1000 for me to get to my tub. I think I will a run dedicated 110 v line to the tub. The circuit it is on now shares with the refrigerator.

My tub does not have an economy mode on it either, pumps come on for 2 mins every 30 and call for heat when needed. I think I will have timer installed and set it to heat/filter once a day and have the cycle end right before I use it around 9:00 p.m., I'm sure my wife will appreciate that as I ask here to do that manually now.

If it turns out to be $100 a month to run the tub in the winter my use justifies it. I would not want to heat a 400 gal tub and deal with a $200 a month electric bill. Maybe It's a good thing I started out with a small used tub.

[ChaiSTi]

Maybe I'm wrong, but I think it's cheaper (electricity wise) to heat with 240V vs 120V. The spa would heat 4x faster per hour. Ofcourse, it'll cost more initial to wire up 240V.

[Dr. Spa]

It heats 4 times faster, and uses 4 times the electricity.

[ChaiSTi]

Did the math and your right about the heater... it's the same to heat up to a certain set point... just A LOT faster... the saving I was thinking about would come from the operation of 230V vs 115V pumps... 230V are usual more energy efficient... unless the spa is using a little circulation pump for heating, I think 230V spas are over all cheaper to heat

[Itchy and Scratchy]

If you live a state with tiered electrical rates like California with 40 cent kWh rates there is no tub that is cheap to operate. Last month I used about 800 kWh for my family of four. The last 300 kwh I estimate the spa used was $100 of the $185 electric bill. I use natural gas to heat with.

Prior to buying this used tub I was looking into a round cedar tub that would have been heated with a 100,000 btu gas heater. 750 gal tub could be heated for $30 a month were I am paying $100 to heat 200 gal with electric. There is more cost to set up with gas but over a 10 year period the savings are huge.

Still looking for anybody out there with ideas about my tub looseing energy somewhere. I'm begining to think it is what it is. Just shocks me that you can go to a tub dealer in California and they will sell you on a $30 a month electric bill on the tub.

I am happy I got this tub, it was only $500. Learning alot about water chemistry and now I have something to enjoy while I research inground acrylic spas with gas heaters.

[Don the spa guy]

If you live a state with tiered electrical rates like California with 40 cent kWh rates there is no tub that is cheap to operate. Last month I used about 800 kWh for my family of four. The last 300 kwh I estimate the spa used was $100 of the $185 electric bill. I use natural gas to heat with.

Prior to buying this used tub I was looking into a round cedar tub that would have been heated with a 100,000 btu gas heater. 750 gal tub could be heated for $30 a month were I am paying $100 to heat 200 gal with electric. There is more cost to set up with gas but over a 10 year period the savings are huge.

Still looking for anybody out there with ideas about my tub looseing energy somewhere. I'm begining to think it is what it is. Just shocks me that you can go to a tub dealer in California and they will sell you on a $30 a month electric bill on the tub.

I am happy I got this tub, it was only $500. Learning alot about water chemistry and now I have something to enjoy while I research inground acrylic spas with gas heaters.

Just a quick FYI... I am doing some energy use testing for the sole purpose of comparing spa cover of different designs against one another on identical spas sitting next to each other. I am using 2 Hot Spring 1996 Classics, both with brand new "shotgun type" 1 KW heaters and brand new 85 watt Grundfos pumps which run 24 hrs a day. The temp on both is being maintained at 103 degrees. The jet pumps are disconnected as are the light bulbs.(no ozone either) Most techs will agree that this spa is fairly well insulated. The covers are openned daily to check water temp for 2 minutes. Warehouse temps in the test period average 50 degrees. Spa covers are swapped once a week to make sure one spa isn't running more efficiently than the other and so on. (Trying to make the cover comparison testing as scientific as possible for the marketing of a newly designed cover.)

Bottom line is the spas just sitting there maintaining 103 are using 5 KWH's per day. Start ozonating, jet pump cycling and therapy use, open covers while in use, colder air temps, etc. etc. that usage will only go up. At 40 cents/kwh each spa is costing $2.00 per day just to keep it hot ($60./month in these conditions) As for me and my spa, it is well worth the probable $75/month wintertime cost to keep my spa ready for my daily soak

[Itchy and Scratchy]

Don, those results will be interesting. How many gals are in the classic you are testing. I should have my kill a watt next week and will begin electrical efficiency testing of my own.

[Itchy and Scratchy]

Got the kill a watt in today. Looks like the tub draws 1.1 kWh when heating. Low speed pump is .25 kWh. That leaves .85 kWh in heat output. In theory this should put out 1.9 deg an hour I am noticing about 1.5 deg an hour. These numbers make much more sense than my original estiments.

Pump is 1/8 hp. Is .25 kWh efficient for that rateing? Could there be saving if I upgraded the pump and heater to something more efficent???

I estimated my tub was using 300 kWh a month. It is closer to 200 kWh a month. About $60 to $70 a month on the electric bill.

I will start a seperate post with details about various heating/filter cycles and energy efficiency. As of now I unplug the tub after my nightly soak and let it heat up a few hours before i get home. I will soon know if it is worth the trouble of doing that.