I am in the final stages of completing my workshop in the Pacific North West (on Vancouver Island, near Victoria Canada). I have two conditioned work areas: one 24ft X 20ft the other 12ft X 20ft (all 10 ft high ceilings) separated by an unheated covered breezeway 24ft X24ft. I have imbedded PEX tubing in a 4in slab on grade floor (in the two conditioned areas) with 2.5in of XPS insulation throughout. The tubes lead back to a small mechanical room in a corner of the unheated breezeway which will be enclosed and insulated. I have a small sink in one of the conditioned areas that requires DHW for washing up - low volumes that can easily be handled by the smallest undersink electric hot water tank. Note: no natural gas in our area, propane is very expensive so electric is really the only choice.
I did a heat loss calculation and get about 17,000 BTU/hr (5KW/hr) for maximum heat loss. In reality our climate has long shoulder seasons and fairly short max heat loss days. If during max heat loss days the shop is a bit cool, that's no problem - it's for hobby use not production use.
The questions:
1. What is a reasonable approach for supplying hot water? The plumber who is doing the installation is suggesting a standard hot water tank with a control that will turn on both elements simultaneously, providing about 7kW of heat input. That should be enough heat input but for much of the heating season you could probably use just one element. He doesn't seem to know of a controller that will activate one or two elements depending on heat requirements. Does such exist? Does it matter?
2. Is a small special purpose boiler a better choice? What make/model would you suggest?
3. If a hot water tank is used, should it be a closed system with supply of my DHW needs through an under sink unit or is a singled combined open system preferable?
4. If a hot water tank is used in a closed system, do you add anything to the water - rust inhibitors? anti-freeze? I seem to recall reading something about the heater elements breaking down the additives in closed systems.
Thanks for your help!
Doug
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