Radiant heating to melt snow in my driveway

Dave_27

Here is my brainstorm - someone tell me why it won't work...

I live in the Northeast and have a gas fired hot water system to heat my house. I want to do new cement in my driveway and bury radiant heating tubes to melt the snow. My driveway is about 15' wide and 20' long.

My brainstorm is this: on the outside of the flue from my boiler (6" duct pipe, about 3' long), I would wrap a coil of 1/2" copper tubing and then wrap insulation around the coil to prevent heat loss. The coil would be attached to a small circulator pump that would move a heated glycol solution through about 200' of tubing in the cement, heating the cement and melting the snow. The cooled glycol would return to the coil, be heated again and continiously circulated. The system would start when a sensor detected a) the boiler was on and b)the outside temperature was below X degrees. For saftey, I would also include an overpressure valve, in case the water pressue rose above X psi.

I realize that the glycol may cool too quickly as it passes through the tubing (making the whole idea worthless). I would appreciate any help on the heated glycol temperature needed vs. the speed the glycol passes through the tubing.

I know this is a crazy idea, but if I could make it work this system would reuse the heat going up the chimney, without any additional cost to me and I can get away from shoveling snow!!!

Any and all ideas on how to make it work (or why it won't work) would be much appreciated.

Thanks,
Dave

jim lockard

snow shovel

Dave--No one likes to shovel, as for wrapping copper tubing around the Boiler Flue NO bad brainstorm your flue and chimney need that heat so that everything works correctly.
Now you may very well be able to pull a zone off you boiler with a flat plate heat exchanger and heat the drive with that as you suggest. Be sure to provide for expanision and pressure relief. 15 feet x 20 feet not a lot to shovel is it? Think snow--J.Lockard

Steve Eayrs

I don't think you could get enough heat to do the job, Dave. The stack temp. is usually not near hot enough, or the burner would not be running near enough.

In a snow melt system you usually need about 150 btu/sq.ft... you have 300 sq.ft......so would need about 45mbtu. Don't know the size of your boiler but can't imagine you have that much total gross stack loss, when the burners running.


A 1/2-way snow melt system doesn't work too well. It just melts enough to make ice out of the snow, or at the best it melts it in stripes, or only melts the area over the first part of the loop(s).


If you did manage to suck enough out of the stack temp. to make this somewhat work, there is a good chance you would end up with lots of condensate rotting out the stack. I imagine this is an older non-condensate boiler.


In otherwords if your boiler is old enough to be throwing enough btus up the stack to make this work, you are already wasting a lot of energy, and I would advise you replace the boiler w/something more efficient and do the snow melt w/ a heat exchanger.


Steve

Mark_25

When you look at the heat required to do snowmelt, the BTU's are large. You won't get near enough heat out into the slab with a 1/2 line, and nowhere near enough by trying to pull it out of the stack temp. Lots of snowmelt systems out there 2-3X bigger than a regular house would need.

Jack_23

I wouldn't do it

Problem is that the exhaust heat is needed to power the flue gases rise out the building. You pull more heat out of the flue gas and you will likely reach the dew point temp. This condensation is acidic and it WILL rust out the vent connector at least and given long enough the boiler itself. Not a question of if...only how long. Do your snowmelt, just use rated and proper components...and a good contractor

Mad Dog

Ain't happenin!

As the other guys said, you'd never produce enough btus. The snowmelt system we just did needs a minimum 95 btus per sqaure foot to melt snow. A safer number is 105-110 btus. Besides, that would be a real rube goldberg job. You'd also be running the boiler all the time - overheating the house. Mad Dog

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scrook_2

the flaw...

in the logic is that your boiler is really nothing more than a cast iron (or copper or steel) tube (if you stretch your imagination) wrapped around the hot flue gasses and covered with insulation on the outside (plus some safety and operating controls...).
Alas (or not, as you're paying for fuel) there is not much heat left in the flue pipe -- some though, and some of it is tied up in keeping the water created (along w/ carbon dioxide) a gas, not liquid. Extra high efficiency condensing boilers in fact get their extra efficiency by cooling the flue gasses further and condensing that water, but it's only a small amount more heat.

Snow melt OTOH needs LOTS of heat (and a boiler that tolerates really cold water coming back to it or a heat exchanger). In theory you might be able to use the boiler (if it's big enough) to melt snow on the drive, BUT you couldn't also heat the house at this time, so you'd get cold when ever it snowed. You could put the coils in and (at a later time?) add a second boiler for snow melt only though but that gets expensive. Never hurts to ask though.

Pat Clark

Besides all the other info

given above, it is also against most codes to alter the flue stack and try to reuse or recycle the heat there. The reason is as stated above, reducing the temp in the stack can lead to condensation and rotting of the flue and equipment.

Pat

Mark_25

His driveway is 300 sqft, and he'd need at LEAST 30,000 BTU's to do this. I don't see anything but a boiler or an oil water heater that can do this job. I'd lean towards an oil water heater, because it's designed for a coldreturn temp, and it could be completely self contained. Expensive not to have to shovel snow though.

Mark Wolff

You hit the nail on the head...

The glycol will cool too quickly. You cannot heat the glycol in the tubing enough running around the stack.