Turn Excess Attic Heat Into Hotwater





Introduction: Turn Excess Attic Heat Into Hotwater

I was wondering if I could heat the water in my swimming pool using the heat in the house's attic and I started messing about with a large <s>heatsink</s> thermal battery. The water for my hotwater heater has to pass through it and picks up free calories which saves on the power bill quite a bit of the year. Even on winter days it adds some heat to the water and every calorie free is one I am not paying for...


Step 1: Make a Big Box.

I was worried about condensation on the pipes and also concerned about freezing even though I live in Florida so I decided to try a large box of sand. I used about two cubic yards and mixed it with two sacks of mortor mix to prevent it from turning into a giant hourglass. In the event the house is knocked down in a hurricane, it will just crumble and that will be one less thing I have to clean up.

Step 2: Stick in Some Pipe

I tried CPVC first because it was easy.

Step 3: CPVC Has a Surprisingly High R-Value

I began to experiment and after modifying a large tank I began to circulate hot water to try and warm the box of sand. After burning everything I could find, I began to realize that for the water to run in hot and back out hot and the sand to remain cool I was not transferring any heat.

Step 4: Boyle's Law

I forgot to keep an eye on it and add water. When the water got low enough for it to start circulating steam instead of liquid, the pressure spiked and it made a very loud noise.

The sand was still cool...

Step 5: Never Fear!

Just make it bigger.

I added 150 feet of 3/4 copper tubing primered and painted to protect agaisnt corosion.

This doubled the original size of the experiment but it began transferring heat.

Step 6: Let It Warm Up

There is enough mass so that the tempurature will only swing up or down a few degrees a day, so in the summer it averages about 90 to 100 degrees. In spring ,fall and most of the winter it is still above the tempurature of the well water, so it is stil benificial.

Step 7: Go Around It in the Cold

I can open an irrigation valve and bypass the water around the box if it ever gets colder than the well water here. I'll use a sensor in the box to open the valve, otherwise it is shut by default.

Step 8: The End

It won't supply all my hotwater, but it does contribute and there is nothing to maintain and not likely to cause a roof leak.



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    hey some one may want to go with PEX Tubing. its very cheep, and flexible. find the right wholesaler and get 500 Ft of 3/8 for under 50 bucks. Many sizes. with easy to use quick connect fittings. I use it at work everyday. makes life easy. I can find out what website we use if any one is interested.

    Interested in your supplier. Need to replumb whole house and putting some solar water heating in while we're at it seems smart.

    G.A. Murdock. Quality products. Been using them for 3 years now. Good luck

    Would Vermiculite work in the place of sand?

    I like Tdrago's idea with the truck rads!! Do you brainiacs think that lengths of PVC piping in an attic would perform as well? Maybe strapped to the underside of the roof joists for maximum heat. Maybe not here in Canada, but for the southern states, I think it would be a lot less building and weight in the attic.

    The pipes would get covered in condensation and drip into the attic but yes it would work during the day.  The idea with the sand was to both store heat for use at midnight and to avoid forming puddles in the attic.

    Next I'm going to try using two or three 40 gallon well tanks buried in the sand. I'm not getting as much heat transfer as I'd like with 300 feet of pipe, the water passes through it too quickly.

    I had originally planned on pipes like you mention inside say a ten inch pipe filled with sand but getting the sand in there would have been difficult.

    Carrying 3 tons of sand up there in five gallon pails was work enough LOL.

    !!!!!!!!!!!!!       DON'T use vehicle radiators!!!!!!

    They use LEAD solder to build them since there not for human consumption. Please be careful!!!!!

    I agree with Nostraquedeo. If you plan to be incontact with the Same water that travels through the Car/Truck radiators, you shouldn't, No Scratch that, Don't use car/truck radiators.

    However, TDRAGO, it's a great thought but the Lead used to solder those together or lead that maybe in the material itself just isn't worth the health risk…
    Still a good thought.

    While it's shut off in the cold the lines could freeze and pop. I know I've had plenty of burst lines because of the cold in the winter but thats usually in the basement. Maybe the attic would stay warmer while the house was heated but if you lost power and the house went unheated say, while you were away on vacation things could get ugly.

     terrific idea. But please make sure the temp of the sand pit stays below 89F & above 140F. Anything in between is proving to be the optimum breeding temp of that Legonairs virus. Shower warm & healthy