Turn Excess Attic Heat Into Hotwater




About: http://senseless.livejournal.com/ I've been attempting to build a house mostly by myself for the last five years... I finally more or less finished it before the bunker project and after recovering from cr...

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...


Teacher Notes

Teachers! Did you use this instructable in your classroom?

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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    73 Discussions

    Timmy P

    10 years ago on Step 2

    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.

    2 replies
    yoga_beyotchTimmy P

    Reply 7 years ago on Step 2

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


    9 years ago on Step 8

    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.

    3 replies

    Reply 9 years ago on Step 8

    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.


    Reply 9 years ago on Introduction

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

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


    Reply 8 years ago on Introduction

    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.


    9 years ago on Step 7

    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.


    9 years ago on Introduction

     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


    Reply 9 years ago on Step 5

    I framed the house with 2 x 6's and then covered all my walls with plywood, glued and nailed every 5 inches for hurricane production.  I centered the mass of this over a 5 by 7 laundry room lined with 3/4 inch plywood and extended well past that with even more 2 x 6's on one foot centers and glued and nailed more 3/4 plywood over it to act as a floor / base, plus that part of the attic is not trussed but framed by hand.

    Regular trusses would not support this weight and it would fall though the attic floor...

    The house isn't built like most stick houses, I went out of my weigh (no pun intended) to make it take a very high windload and can sleep right through a tropical storm without a creak.

    It's like a bunch of shipping containers tied together to form the rooms on the main floor.

    I forget the load a standard truss can support but it is well below the mass I have sitting up there.

    Overall I used 7 bunks of plywood, bundles, and about 50 cases of liquid nails, then covered that with sheet rock so it appears like a normal wall inside and a side effect is that inside the house is extremely quiet even though I live 500 feet from an evacuation route, US 331.

    You can hear the traffic in my vids done outside but not the ones done inside.

    For a stick framed house it is very very stout.


    12 years ago on Step 8

    For a given volume, few materials are better than water in terms of heat capacity. Water is also more easily moved (ie via a garden hose) and has better heat transfer to pipes running through it due to convective heat transfer. An alternative design would be to run your pipes through 4 or 5 plastic 50 gallon drums filled with water (and antifreeze). These can be picked up for about $15 each used.

    2 replies

    Reply 11 years ago on Step 8

    I could probably get away without antifreeze here in Florida even with consecutive freezing nights the mass never got below 55 degrees. I'm thinking of redoing it using a few 400 foot rolls of that polytubing people use for sprinkler systems because the water here is so low in Ph that it corrodes the copper big time. I think if I run 3 or 4 parallel tubes of one inch 400 feet long I think I'd get enough water flow to not effect the the flow of water to the tubs or showers, but would keep it within the heated area long enough to make up for the insulating value of the plastic tubing. It's not rated for hot water but it won't get much hotter than 100 degrees and seems to average around 90.


    10 years ago on Step 8

    if some one wanted bigger they could put it in a commercial building


    10 years ago on Step 8

    ** A MUCH easier way would be to just use 1 or more old truck radiators. The bigger the better.
    These are meant to contain hot water and only release water when the temperature of the cap is exceeded.
    They could even be directly attached to the undersurface of the roof or elevated near the roof for maximum heat transfer. You could feed one radiator into a second or more radiators thereby further heating the already heated water... Might get TOO hot!
    You could even get fancy and add a thermostatically controlled fan. There is a commercial product along these lines. See: http://www.solarattic.com/pcs1.htm


    11 years ago on Introduction

    I'm sales of heat pump factory from china. I love my job as every heat pump unit will help to save the energy of the earth. Each unit will keep the earth existing 5 minutes longer. Through creative experience of many years, Chengda Eco-tech research center excogitated large, middle and small energy-saving and environmental friendly air to water Heat pump, swimming pool heat pump, water source heat pump heater, DC inverter air conditioner, duct air conditioner, ceiling cassette air conditioner, real VRV air conditioner. With our long years experience in heat-pump technology, it makes full use of the energy from the recyclable resource like air, sunshine, water and so on. It brings a revolution to the energy-saving industry.

    2 replies

    Reply 10 years ago on Introduction

    "Each unit will keep the earth existing 5 minutes longer. " Is this really a bragging point, considering the only way the Earth with cease to exist is when the Sun turns into a super-nova in a few million years? I doubt your water heater can stop that from happening.....