John,
I had a de-icing system at the car wash. I added on to the heated area but not to the boiler capacity in 2003. In the area I added to, I did it by modern standards with insulation under the concrete. I can tell you with certainty that when the system was "on", no snow accumulated on the added section, regardless of storm; no ice formed either. It was almost as if that slab was in a different world.
The difference between a de-icing system at a car wash and a residential snow melt system is notable. The de-icing system must operate to prevent the formation of ice down to the design point; in our climate, it's about -10F. It turns on at about 35, and cranks more and more heat into the system as the outside temp drops. At a car wash, it is on based solely on temperature because water is flowing all the time, and if it wasn't on, you'd freeze quickly. You don't need as many BTU's on a snow melt as you do on a de-icing system.
A residential snow melt operates a bit differently using the same hardware. You turn it on in anticipation of precipitation either snow, sleet or freezing rain. These three nasties, believe it or not, generally fall between a narrow band of temperature. Much below 25 or 20 degrees, we often don't have any precipitation falling (perhaps in Northern Canada or Antarctica, but not often here). Above 35, it's rain. Once the precipitation has stopped, you turn it off.
So, we have a few snowfalls in January, you turn it on. When we have days or weeks of freezing weather, but no precipitation, it sits there. No cost to run a system that isn't on.
I'll have good info on cost to run once it is all running. I even bought a gas "sub-meter" so I can measure the gas used by the heater for this system, which is a 140,000 BTU tankless water heater. If it were a de-icing system, I'd have to go to 190,000 BTU.
Why have I done this? It takes me about 90 minutes to clear my driveway after 4" of snow. Those 1" falls are even more annoying--too little for the snowblower. The big snowfalls--6" or 8" or more, generally take two or more passes. If I contract it out, it can be $350-$450 per season; and they come when they get to you, not when you want to get out. Some roving guys--if you catch them, will do it for $25 per push. No matter how you deal with snow, it costs money; it takes time. Nobody ever had a heart attack (not that I'm planning on one!) turning on a snow-melt system. You can burn gasoline in a show blower; you can pay someone to do it with a plow, burning gas or diesel. You can spread up-teen pounds of corrosive salt or calcium chloride to help you in your cause, at a cost of $5 to $25 a bag. Winter 2007/2008 there was a feigned shortage of salt and de-icing compounds so the price skyrocketed and availability was non-existent. The space I have to clear is simply too large to do it by hand, you need energy-consuming tools. A snow melt system built in is simply another energy consuming tool. So until I move to the Southwest...
There will be a non trivial operating cost. I don't believe some [equipment vendors] who say $100 per season. I also think that those who have them and shut them down because of cost to run might not have had them designed or fired properly. We'll see. I worked with my car wash supplier who has installed hundreds of these and repaired plenty, too. They know more about this stuff than any heating contractor, simply because of decades of real-world operational and installation experience. Most heating contractors know almost nothing about radiant systems for this application. There will certainly be some tuning and learning involved. We have designed balancing systems into it so we can tune the system based on operational characteristics, not theoretical design. Factors such as where the sun falls on the driveway and when make a big difference in how it all works. We're prepared for tuning it.
How can your municipality tell you you can't have a snow melt driveway? Is it the gas consumption? Are they in the gas business? What if you had a geothermal-fired system? Or solar? Or wood fired? There are all kinds of ways of making the heat needed for this. I have 5/8" tubing, 1 linear foot per square foot of driveway, done in 7 zones/loops generally around 300' each. It is tied to 6 x 6 steel mesh; it sits on 1 1/4" insulation on top of 5" of pea stone base. The concrete is 5" of 6-sack, fiber reinforced, 4000psi. The tubing is raised 1" off the insulation.
