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I got a crazy idea. Well not original but still crazy. Back in college we use to put out a small pool every summer. At night it would get cold in that pool. So we would duck tape the hose to the kitchen sink and turn on the hot water. It was a complete waste of natural resources and we did not have a clue about it, we were kids in school. Sooo, some time later I can use that experience with my kids. As we all know the water from the hose is very cold. Why not fill the pool with hot water? Because that would be a waste right. No, not in my case. Why? Because I have a hot water heat pump. That’s right. Heat goes into the water and cold air comes out the top. Since that cold air is going to offset my whole house AC system it does not waste anything or cost anything extra.

So I heated the pool for my 4 year old daughter. She loved it! No, I did not duct tape the hose to the kitchen faucet. I went to the store and purchase a boiler valve and a tee brass fitting.  I did it the right way.

I also drained the pool with a pump and used that water to water my garden and plants. Double bonus! That is why  my kids call me crazy daddy.


I think this will work for now. I have the big tank at 120 degrees or so. Since the big tank feeds the little tank, I can only make a good guess based on the dial. (normally, I measure the water temp. with a small thermometer) I have the thermostat on the little tank at 123 degrees. The interesting thing about the little tank thermo is the trip-on setting. I am not 100% sure but I think it has a -7 setpoint trigger. That means the element turns on at 116 degrees. This means that the little tank will not turn on unless the water has sat for some time or the incoming water drops below the trip-on point. So the little tank is a buffer.

After a week with this setup I have about the same heat pump energy usage and a much improved little tank usage of about 1kW a day. It is better for me to use hot water throughout the day. (no need to wash hands is cold water) Why? because the big tanks outgoing water will help keep the little tank from turning on.

What does the wife think? She just want hot water when she wants it. i.e. don’t mess with my hot water!

So I would say it is the middle of winter. Maybe not by the calendar, but the thermometer says so. From my observations, the electricity usage for the hot water heat pump have increased from 3.33kW hours to about 4kW hours per day on average.  This increase can be attributed to three factors.

  1. The incoming water temperature has decreased because of colder ground temperatures.
  2. The heat pumps ambient air temperature has decreased.
  3. The shower “anti-scald valve” has caused me to increase the tank temperature.

Factors explained.

  1. This is easy. Colder air temperatures cause the ground temperatures to go down also.
  2. I would say the air temperature in the summer for the heat pump was about 80 degrees. Now it is around 60 degrees.  This makes the heat pump work heard to get the tank back to the set point.
  3. The shower fixtures in my house have a anti-scald valve. This is for safety. This means that cold water is always mixed with incoming hot water and that comes out of the shower head. I use to have the tank set at 120 degrees. Now I have to have it set at 125 degrees to get the same hotness of water at the head. I was also informed today that “my shower was not hot enough”, so I may have to increase the tank temp. again.

If I had my old gas tank, I would only have to deal with 1 and 3. Personally, I think it is 1 and 3 that are causing the biggest increase in energy usage. This means I am still money ahead in using my hot water heat pump.

I have had my new Air Vent installed for a few days now. Nice cool air for a few hours in the early afternoon. Installation was very easy. Total time was about 1 hour and 30 minutes. I had to install a “Street Elbow” to make room for the Air Vent because originally the expansion tank was in the way. I only had to shut the water off and screw it in.

Air Vent Installed onto the Air Tap

Air Vent Installed onto the Air Tap

My only complain is that they should have made it the same color white as the Air Tap. But it is in the basement and I did not buy in because it looks pretty. I am still trying to quantify the savings the Air Tap will have on my electric bill from the cooled air waste product. If the unit runs for 5 hours a day. That would be a net increase of 35,000 BTU of cooling into the house. That is the same as runing my AC for well over an hour. Maybe now that I have the cooled air directed to somewhere useful I will see an impact.

That’s right. I almost ran out. My in-laws were in town. So, I took a shower, then my father in-law, then my wife, finally my mother in-law. All of that was in about an hours time. Then 45 minutes later my 2 year old daughter takes a morning bath. (She missed two nights in a row. Why, because every time we asked she said, “NO!” got to love ‘um at two years old.) As we all know baths use more water then showers. My wife yells down to me, “we are running out of hot water.” I kindly explain to her the our old water heater would have barely made it past shower #2 let alone four.   Then you want it to fill a bath tub. Ha! I think it did very well.

The heat pump then ran for about five hours. Worked great. and as it should have. I am very glad I went with the 80 Gallon tank. For awhile I was thinking that I went to big. Maybe the 66 gallon would have been better. Now I know I made the right choice. Years from now when all four of us are taking showers in the morning I will know I have enough hot water.

I received and installed my new and improved Tstat yesterday. I think I installed it up side down. But once it is set I probably won’t mess with it again. The temp bulb does extend down about an extra foot. This will help too start the unit sooner and hopefully won’t run it for as long. I worry about it freezing up in the winter when basement temps are cooler and it runs for four straight hours.

Removal and installation took about and hour and a half. Not too bad. Took my time and was trying to work smart. For a small moment I thought about just leaving the unit shroud off. I thought the improved airflow would help with efficiency. But, in the end I thought it better to leave it on.

I now have the temp set at 110 degrees. I hope I can keep it this low. Water is hot when I want it and no one has complained. When the thermostat bulb now lower in the tank I hope that this help start the unit sooner. Also, the thermostat is only a 10 degree on/off hysteresis. After the unit did kick on I noticed it did not run as long. Three hours instead of four or more. Will this reduce electricity usage. Maybe. The tank temp of 110 degrees most certainly will.

I installed my new hot water heater and hot water heat pump this weekend.  Works perfectly (Almost)! I decided to purchase an 80 gallon Whirlpool lifetime tank and a heat pump unit from Air Generate. Together the total cost was about $1100. $600 for he water heater and $500 for the heat pump. Since my old unit was not in the best shape I could deduct the cost of the tank, but I switched from gas to electric and you can buy smaller gas water heaters because the recovery time is usually better. I figured on about $400 dollars for a new gas tank. That would make the upgrade cost about $700.

Installation was a trip to say the least. Actually, the biggest problem was removing the hot water nipple from the new tank. The nipple only extends maybe a half inch from the top of the tank. In the end I had to buy a huge 16″ channel locking pliers, set the tank on the floor and use my weight to finally get it to come off. The nipple was destroyed but I was not needing to use it again anyway. That fiasco took over three hours.


After the nipple was removed the remainder of the process was very straight forward. The instructions do a good job explaining everything. Air Generate also has an installation video on their website. After everything was done I only had one leak. It was from the fitting that passes the thermostat wire outside the tank. I just added some Teflon tape and tightened it down. No more leak.

Some time ago I purchased an extra Kill-a-watt. Now I can see exactly how much electricity this unit uses! With that,  I filled the heater full and bleed out all the air. The heat pump ran for a little over 6 hours and used 3.33kWhrs of electricity. The temperature was set to 115 degrees. I just looked at the Kill-a-watt and it now reads 12 kWhrs over 72 hours. That would be 4kWhrs a day. But, I also raised the temp setting to 125 degrees. The main reason for raising the temperature is because the tank is so big and the current thermostat has a 15 degree on/off hysteresis. My I take a shower cold water enters the bottom of the tank. Then ,when the wife jumped in an hour later the tank temperature would even out to around 100 degrees. She did not like taking a shower at 100 degrees. So I had to turn it up.

The current thermostat is only 26″ long and the new one will be 38″ long. This will allow it to extend further down the tank. Thus after a shower the unit should turn on. Also, the new thermostat will have a on/off hysteresis of only 10 degrees. After I install the new thermostat I will go back down to 115 degrees. This should bring the electricity usage back down. (I found out about the new thermostat after I called about the leaking fitting. They are sending today. Customer service was very good and helpful. On the phone and Email!)

One more important thing to note. I DID NOT PLUG IN THE WATER HEATER! That is correct. This is just a storage tank. The tank has a lifetime warrenty. So hopefully, I never need to mess with another tank again.

In another blog I stated that it was better to get a solar hot water heater instead of a add-on heat pump. I have changed my mind. Here is the reasons why.

One, I want to turn off the gas service to my house. Normal solar heat exchanger tanks use electric anyway, but during the winter when the sun does not shine very much I would be using the electric backup a fair amount.

Two, I have limited roof space. Even though solar heating is more efficient then solar electric, electricity is more versatile. With the limit space I would like to devote as much as possible to PV panels.

Three, the add-on heat pumps waste product is cold air. This could help with my AC bill in the summer. Since the water heater is located in an unconditioned space in the basement the waste cooling would have little effect in the winter.

Lastly, if a solar hot water system is designed correctly, in the winter I will need to use the backup heating elements. Then during the summer I will be wasting thermal energy because I simply can not use it. Utilization increased in the summer leads to more backup in the winter. More output in the winter leads to more waste in the summer. With the heat pump feed by future solar electric, there is no waste. What electric I don’t use is given back to utility to use at a later time.

airtapI have purchased a heat pump from Air Generate for $550. I am planning on purchasing an 80 Gallon water heater from Whirlpool. I will not be paying $800 because it is cheaper in my area. I will then mount the heat pump onto the water. Then set it in place. I have the 30amp 240V line already run to the location. I may not even connect the water heater up to 240VAC.  But a nice feature of this water heater is anti-freeze setting. The heat pump runs off 120V. FYI-the reason for the big tank is it has better insulation then a smaller ones and I want to set the temperature at 110 degrees for better heat pump efficiency. Thus the need for more holding capacity. As always I will post the finished product.

Total cost estimates are about $1200. This is about $800 more then if I just replaced my gas unit but I don’t think I will ever run out of hot water. And I get “free” AC in the summer.