Just An Idea

Q: In my area cold water inlet temperatures often drop to almost the freezing point of water. I have recorded temperatures as low as 34F in January when the frost get down to about four feet below ground. The average temperature in my basement where the water heater and furnace sit remains about 66f all year. I had though of putting in a second bare tank to receive the cold water before the water heater, allowing it to heat up to room temperature before entering the water heater. Any thoughts?

A: Too an extent, that's true. If you cool the basement much, it will cost more to heat the house. That said, it won't cool the basement a great deal. But instead of a tank, I'd use a coil of copper tubing. Place 2x4's between each coil, in line with other, to keep them separated. Vertical would need a stabilizer I would consider installing a copper 'vertical ground loop' a few feet below the frost line to push heat into the water more directly. Something like: http://blog.futurelab.net/vertical_ground_loop%20-%20MH.gif I would heavily insulate the tubing that was above the frost line. I figure that a bare tank in the basement would have too poor a coupling to the temperature of the soil to do you much good. If your water heater is located in the basement, lowering the ambient temperature (with the bare tank) would make the water heater run longer. Looks like you can do it if you bury your uninsulated tank in the basement floor. (Thermal conductivity of air is 0.0126 or about 2000 x lower than that of your steel tank.) Let's grab an American envelope and a pencil. 40 gallons of water weighs about 333 lbs. It will require 333 BTU to raise the temperature of that water by one degree F. From 34? F to 66? F is a difference of 32?. To raise the temperature of the water in that tank to within a few degrees of local 'earth normal' will require over 10,600 BTU/hr. (And that is for 'no flow' conditions.) Thermal conductivity of 1" thick steel is about 25 Btu/hr-ft-? F If the walls of your tank are say, 0.05" thick, you will be able to push 500 BTUs per hour through each square foot of tank surface for every degree of difference between the inside and outside of the tank, or 16,000 BTU/hr per square foot for a 32? difference. Note that as the water warms up, heat flow decreases significantly. Neglecting the top and bottom, an 18" diameter tank 40" tall has an exchange area of over 15.5 square feet for over 7800 BTU/hr/degree. Leak detection and corrosion control is left as an exercise for the student, on an hourly basis. I *still* like copper pipe better. It has 2.5x the thermal conductivity of your tank and lots more surface area, for a correctly sized loop.

Discuss It!

Most Popular Articles

More