What about going to Canadian Tire and picking up some heat tape...it also could be called heat trace? It is a long warming cord that is actually wrapped around water pipes under mobile homes to keep them from freezing in the wintertime. It looks like a funny electrical cord that has a thermostat on it and actually is fairly inexpensive. When wrapped around the waterpipes it keeps the pipes just above the freezing point but still cool. We used one in the basement of our greenhouse/potting shed for years (to do just as you would like to do) until a cold storage area was built in our basement in the house.

Thanks for the suggestion. It sounds like it will fit my requirements to a tee.

Such an old post , let's add some value to it.

If one could run his cold water service through this insulated building he /she could pull some heat from the cold water and help to heat the building. The water would only flow when required for use in the house.

Another source of heat is the waste from refrigerators in the house. If you can put one of the freezers in the storage building you'll get some extra walking time in and you'll use the waste heat to heat the unit. Plus you might save on cooling for your frozen foods.

Think. Think think.