Radiant heat for driveway?

[redsand187]

Something I've been thinking about.

I've got a steep driveway, that needs to be replaced next year. It's steep and not fun to clear when it snows.

I've seen some electric heat systems that is put in the concrete to melt tracks so you can still use your driveway. Seems kind of half *** to me, if I'm going to melt snow, I want to melt it all, not just a couple tracks. Unfortunately, these things are spendy.

So, radiant heat systems using water/glycol mixes seem to be all the rage for heating shops on this forum. Has anyone here done a system for outside?

I've got about 1000 square feet of driveway. Temperatures never get below the single digits, so I'd think a standard mix like 50/50 glycol would be plenty to keep the system from freezing up even if not on. An electric boiler/water heater, and pex looped through the slab seems pretty simple.

The real question I am wondering is how to calculate heat loss in a loop? The loops would need to be a minimum of 80ft long to go down and back up the driveway. So would say 10 degree slab temp be too much to overcome to raise up 40 degrees or so?

I'm thinking it may be possible to do a system like this for cheaper than the $8-10,000 an all electric system appears to cost.

 

[tdkkart]

They just did a couple sidewalks/approaches at work. 1" tube, 6" on center throughout the whole slab. I don't have the calcs in front of me, but that's ONE HELL OF A LOT of BTUs being dumped into that concrete.
Every BTU that gets dumped into the slab has to come from somewhere, which means a heater that produces ONE HELL OF A LOT of BTUs.

They can do it at work because they have enough boiler capacity to heat several million square feet of building down to well below zero degrees, another 1000sq/ft won't even dent the useage.

 

[7thDimension]

Although an interesting idea, I think it would take a literal **** ton of energy to raise and maintain the temperature of the slab enough to make a difference. You have to put enough energy into it to compensate for the heat loss from radiation into the surrounding snow and air.

I think the driveway would just act like a huge heatsink...

 

[98ssuck]

To make it economical to run a wood fired boiler might be attractive option. You could run the loops selectively to just heat the area of the driveway you drive and walk. Heating the entire driveway is going to be expensive to operate.

 

[stikman56]

I think I'd heat it with wood, otherwise just gonna cost a fortune I would think.

 

[tdkkart]

You can't just selectively heat. What do you suppose happens when you melt the snow, and then the water runs away, UNTIL IT FINDS A COLD SPOT, and then it's ice, all the way around your nice clean patch.

Picture a nice long 6ft wide sidewalk sloped to an unheated parking lot.
What do you suppose is at the end of that sidewalk during a big snow storm??
AND, the concrete is wet, guess what sticks to it when the wind blows across the sidewalk??

Yep, any place that's not heated, or isn't heated enough or well drained becomes a skating rink.

 

[Thumper68]

There are a few higher end homes around here that have either hydronic or elec heat in the aprons and sidewalks. I would hate to see what it costs to keep them ice free.

Come to think of it when my buddy built his house we put the elec resistance heating cable under his slab in the basement. garage and apron. I seem to remember him saying that it was a good idea but way to $$$ to use on a regular basis.

in a house we had many years ago I had a good grade coming up to the garage, I would snow blow followed by the leaf blower to get the little that remained off the concrete.

 

[redsand187]

You can't just selectively heat. What do you suppose happens when you melt the snow, and then the water runs away, UNTIL IT FINDS A COLD SPOT, and then it's ice, all the way around your nice clean patch.

Picture a nice long 6ft wide sidewalk sloped to an unheated parking lot.
What do you suppose is at the end of that sidewalk during a big snow storm??
AND, the concrete is wet, guess what sticks to it when the wind blows across the sidewalk??

Yep, any place that's not heated, or isn't heated enough or well drained becomes a skating rink.

There is a sewer drain at the bottom of the driveway, so hopefully the melted snow would drain there.

I think the system would be a little different than the typical floor heater. That is why I'm asking.

Couldn't you theoretically get a hot water heater, like a 55 gallon one, have it heat up to 160 degrees, kick on the pump, which would then pump the 10 or so gallons of "water," from the lines back into the 55 gallon heater. So you are effectively only heating 10 gallons of water at a time, which is being diluted into 45 gallons of 160 degree water.

That is why I'm wondering how you'd calculate how much heat is lost, also, what the best circulation rate would be. You could pump it through there so fast that it wouldn't really cool down, but then it also wouldn't really heat up the slab either. I don't recall exactly how high the slope is, but I'd estimate it's probably around 15 feet of rise, which brings in more interesting requirements, as most of the standard radiant pumps don't really circulate much volume at that high of head pressure.

 

[redsand187]

There are a few higher end homes around here that have either hydronic or elec heat in the aprons and sidewalks. I would hate to see what it costs to keep them ice free.

Come to think of it when my buddy built his house we put the elec resistance heating cable under his slab in the basement. garage and apron. I seem to remember him saying that it was a good idea but way to $$$ to use on a regular basis.

in a house we had many years ago I had a good grade coming up to the garage, I would snow blow followed by the leaf blower to get the little that remained off the concrete.

We've got great "cascade concrete," snow here. It's freaking wet and heavy, I wish we could use a leaf blower. The driveway is so steep that a fully tracked snow blower is the only type of snow blower that would have a chance of making it up the driveway.

Typically, it snows here, and then in a day or so, mostly melts away... except the driveway, which is north facing. Snow will stay there until like August unless you shovel it. So having a self clearing driveway would be nice.

I will admit this is kind of excessive as it doesn't snow here that often, maybe 10 times a year on a typical year. But when the house was built 24 years ago, it was something considered. Now, with having to tear the driveway out and repour it, it is worth considering looking into again.

Electricity wise, we've got some of the lowest power rates in the country, so as long was only turned on to clear/prevent the snow from sticking, it likely wouldn't be too crazy to bear the cost off.

One thing I do know, is if I spend the money putting in the a system to melt snow, it will surely never snow again.

 

[redsand187]

Although an interesting idea, I think it would take a literal **** ton of energy to raise and maintain the temperature of the slab enough to make a difference. You have to put enough energy into it to compensate for the heat loss from radiation into the surrounding snow and air.

I think the driveway would just act like a huge heatsink...

Hopefully, we'd really only have to raise the temp like 10 degrees. It normally doesn't get below about 20 degrees when it snows. So if we can raise the surface temp to above freezing, hopefully snow would melt on contact, preventing it from even accumulating, provided the system was turned on right before it snowed.

 

[rancherbill]

Couldn't you theoretically get a hot water heater, like a 55 gallon one, have it heat up to 160 degrees, kick on the pump, which would then pump the 10 or so gallons of "water," from the lines back into the 55 gallon heater. So you are effectively only heating 10 gallons of water at a time, which is being diluted into 45 gallons of 160 degree water.

NO!!! A water heater cannot not heat water fast enough!!! You will need a boiler to be able to get enough heat. Think about your own water heater. Can 2 people have bath or showers at the same time? No, you run out of hot water. When you want to heat the driveway, you will need continuous hot water and only a boiler can do that.

Some businesses and private home do exactly what you are proposing. It is doable.

 

[tdkkart]

Couldn't you theoretically get a hot water heater, like a 55 gallon one, have it heat up to 160 degrees, kick on the pump, which would then pump the 10 or so gallons of "water," from the lines back into the 55 gallon heater. So you are effectively only heating 10 gallons of water at a time, which is being diluted into 45 gallons of 160 degree water.

Short answer.....No.
A 50 gallon water heater, especially an electric one, up against 60,000lbs worth of cold concrete is roughly equivalent to a fart in a hurricane.

 

[stingry]

What you are looking for is a snow melt system, they are used in carwashes to keep ice from forming when used in subfreezing temps. Find a carwash equipment supplier and they will probably design the system for you if you buy the equipment from them. I use Dultmeier Sales out of Omaha, NE for my carwashes.

Cheers
Steve

 

[BeachBoy]

"literal **** ton" and "fart in a hurricane".

I spilled my coffee.

People are **** about this topic hehehe

 

[BeachBoy]

On the subject, there are houses that have heated driveways, more and more.
I'm curious to know how much energy it takes and the system they have.

They likely maintain the slab at the bare minimum like 40F

 

[roscoe2000]

Using a Radiant heat on a driveway to melt snow, has been done. Yes it will cost you, but you only need to heat the drive way, when you have snow or freezing rain in the forecast. As long as you can keep the temperature of the payment about 33 degrees (say 35) the snow will melt. There will be not need to run it the the whole season and around the clock, only when needed. Since you need to replace the slab away, and it what you want....it will work...it has been done....and just think how nice it will be when you are looking out the window as your neighbor are shoveling snow and throwing deicers......with a hot cup of coffee and your driveway is clear.....

 

[6768rogues]

I have seen them a number of times at previous jobs. They are called ice melt systems in our part of the country. Some have a dedicated heat source and some have a heat exchanger that uses boiler water for a heat source.
The systems work very well and do not use a lot of energy. Our typical winter day is in the 20's but can dip to zero or below. The system keeps the surface at 36 to 40 degrees, so there is not a huge differential between ambient temp and the surface temp most of the time.
Insulation is placed between the the heated material and the ground so the heat is not absorbed quickly by the underlying ground.
At a school where I worked, a large monumental stairway at the main entrance was heated. I went there one weekend night in a snowstorm and there was not a flake of snow on the stairs. Compared to paying someone to shovel and chip away ice, buying and spreading salt and paying for salt damage, the energy used is quite affordable.
Ours were computer controlled by our energy management system, but for residential use you can buy a controller that will monitor temperature and snowcover, and run the system on its own.

 

[buddyboy]

don't need to worry about water run off

the air is so dry the melting snow evaporates.

insulate under the driveway, and turn on the system when you expect snow fall.

you want to melt the snow as it falls, if you wait till you have accumulation it will take longer and be less effective.

when it stops snowing turn system off and your drive will be dry to the touch

the colder it gets the less water vapor is available in the air to form snow (in general) so most of the time you'll only need to increase the temp of your slab 5 to 15 degrees F.

I too have a long steep hill, I've looked into heating it with a wood boiler... biggest obstacle (besides cost) is the process of laying foam insulation, then tubing then mesh then concrete on a hill that is 400 feet long at a 20 deg incline.. that process will need to be well thought out along with a good crew

 

[Jackfre]

I did snow melt in my sidewalks and the apron (10') off the garage. I had a lot of elevation change on the sidewalks and it was really nice to have a 3' snow storm and have straight edges down to the sidewalk and dry sidewalks. The previous sidewalk was such a liability being on the north side of the house and literally inches of ice. As well, it took so much snow melt to keep it sorta clear that you ruined the carpets and floors tracking it in. I had the driveway apron on a separate zone. I ran them both manually. I built a long tube and shell hx out of pipe to isolate the glycol zone. I had enough boiler to drive it and it worked well for us. I disconnected it when I sold the house and spoke with the new owners about what would be necessary to bring it up to snuff from a code standpoint. If we were going to get a storm I'd turn it on prior to the snow fall. It is better to get ahead of it rather than trying to catch up with it

The point about the run off should be a primary concern. My place was on a slope and I made a bit of a dry well to handle it and I ran the tubing out to keep it from freezing.

My driveway climbed out of the hole too. I had a tractor with a front blower but it was to tight a space to run it effectively. I went back to a walk behind Ahrens snow blower, 8 hp I think, and it was the balls. there are better ways to spend your time but this system worked for me. Doing the whole driveway would have been nice, but a very expensive proposition both from a construction and a operational standpoint. When I ran the system that I had I never looked back. I just paid the gas bills.

 

[toplessHO]

have you seen the demo on u tube of the Russian throwing out a cup of boiling hot water
from his apartment window and it hit the ground as ice? Granted its not that cold where you are but it paints a good picture of how much heat loss there is.

 

[toplessHO]

and it would help by placing high density foam under the slab to insulate somewhat.
You need to then build the slab as a floating type design

 

[toplessHO]

what is your median temp? Might want to try a GSHP with boiler supplement

 

[Jackfre]

Oh yeah, heat loss. I forgot to mention that I went down a foot and put a good stone base, 2" of poly-isocyanurate insulation below and edges. This is a real project.

 

[anthony666]

i have done hundreds of snow melt jobs .. i just skimmed through the previous posts, so sorry if i double up on info

the way that a snow melt system works is this; 99% of the time it's in an idle mode, maintaining the slab just above freezing .. a sensor or manual input raises the temperature high enough to evaporate the snow as it lands so the water runoff doesn't just roll off your slab and form a massive skating rink .. that requires an incredible amount of BTU input, an expensive control system or 24/7 monitoring and a boiler capable of handling outrageous return temp differential and still producing high output temps .. half inch tube doesnt have the capacity to deliver the BTU's per square foot for the task, we usually use 5/8ths or 3/4" he-pex .. also remember that glycol ***** at heat transfer and pumping capability, so keep your mixture as weak as you can get away with and upsize your boiler and pump HP accordingly

typically i do these systems around public buildings, malls, loading docks or rich folk homes

here's a few tube layout snapshots;

a porch that was just tied into the home's hydronic heat via a heat exchanger
https://scontent-a-ord.**.fbcdn.net/hphotos-xaf1/t31.0-8/p417x417/271653_10150291527405792_1579405_o.jpg
loading dock for a shopping mall
https://scontent-b-ord.**.fbcdn.net/hphotos-xpa1/v/t1.0-9/561648_10151292853360792_894363711_n.jpg?oh=cb4b003fc508122983ea2f3478ed1f82&oe=54E7314C
rich folk house
https://scontent-b-ord.**.fbcdn.net/hphotos-xfa1/v/t1.0-9/184809_10151291406735792_753808925_n.jpg?oh=4cd832fac673259c23884cf34ef87721&oe=54E93266

 

[bzinsky]

You can use a hot water heater. Hot water heaters have all kinds of different btu outputs, just like a boiler. They are also more designed to heat up cold water, unlike a boiler which has much higher return temp.

I'd get yourself a high btu water heater, and then just kick it on the circulating pump when its about to snow. Probably wont have an ounce of hot water while its running, but

As for cost, its really not that expensive when you consider how much you pay to have someone shovel. $20 in gas to for hot water is a lot of hot water.

I'd just put on a circulating pump on a high btu water heater. That of course depends very much on how much surface area you are heating. If its just for a couple cars, thats probably not that much.

Fundamentally, it really shouldnt take that many btu's to keep a small driveway above freezing temps.

The big projects the guy above is doing has different needs, you just want the snow to melt durng the storm, its not like you cant throw a little salt down after you turn it off.

Edit: its usually cheaper to hit a specific btu output by using 2 smaller water heaters. Those big high recovery units cost a lot.