# Has anyone heated there driveway????



## bulldogbones (Sep 16, 2010)

So my wife and I decided to pour a concrete driveway.... or  call it a pad, its only 22'x41'. But I thought hey why not lay down some pex and fill it with antifreeze and heat it with my boiler this winter and never have to snowblow the driveway.

Ive been doing some searching but cant seem to find out what diameter pex and how far to space it. I know it needs to be no less then 2" and no more then 4" in the concrete. And since im pouring a 6" pad that will work out perfect and I will lay it at 3" deep.


----------



## soupy1957 (Sep 16, 2010)

Has anyone heated THEIR (sp) driveway?

No

-Soupy1957


----------



## stee6043 (Sep 16, 2010)

I did a fair amount of reading on driveway (snowmelt) systems.  The bottom line I came away with was the ungodly amount of btu's it takes to accomplish snow melt.  For me snowblowing the driveway is a LOT easier than adding another 4 cord to my wood piles!

This site might be useful:

http://www.radiantdesigninstitute.com/index.html


----------



## heaterman (Sep 16, 2010)

In your area you should figure at least 150 btu's / sq ft so you are talking about 80-90,000 at minimum. What size is you boiler? Also of concern is low temp protection for your boiler.........unless you have a garn...........returning 20-30* water to your boiler can lead to some really ugly consequences. 

Tube spacing depends on a few things but basically you will find 9" to be average. Tube size depends on the length of the loops. The issue there is that when you get past a certain length you have no temperature left to do anything with. Most I have done unless very small (sidewalk) have gone in with 5/8" or 3/4" pex if the loops get much over 100' in length.


----------



## DaveBP (Sep 16, 2010)

The other side of melting ALL the snow off to avoid using the plow or snow blower is the interesting drainage problem it can create. How do you get rid of that much water during very cold weather without it creating an ice problem nearby?

The other tack is to plow or blow off most of the snow as though you didn't have the ice melt system and then use it to keep the drive and walks ice free as needed. A lot less heat (cordwood) needed that way.

Either way I think you do need to think about very cold return water temps, as noted.


----------



## Singed Eyebrows (Sep 16, 2010)

I read many years ago that driveway melting is not an on/off thing. You heat the slab in late fall & let it go all winter. You should have a more consistant return temp that way, during bitter cold it still would probably be quite low, Randy


----------



## 4acrefarm (Sep 16, 2010)

I was going to ask this very question. I have a small sidewalk and a small portion of the driveway I would like to do. This would be just in Icy situations done manually. What kind of temps do you need to melt ice?


----------



## benjamin (Sep 16, 2010)

Theoretically you could melt snow with groundwater temperatures.  Anybody have any experience with this?

In my single days I experimented with direct geothermal energy (pumping well water through a radiant slab) it kept the place from freezing, but kept me single also.


----------



## stee6043 (Sep 16, 2010)

If it's just a hobby or something to occupy your time - that's one thing.  But the cost/benefit of using fuel to clear sidewalks and driveways is going to be very hard to justify for residential applications.  Shovels and snowblowers are wicked cheap and easy to use.  Isn't that why we have kids?  ha


----------



## 4acrefarm (Sep 16, 2010)

I am not looking to clear snow, my thoughts are for icy conditions, mostly for safety when I get older.


----------



## Chris Hoskin (Sep 16, 2010)

4acrefarm said:
			
		

> I am not looking to clear snow, my thoughts are for icy conditions, mostly for safety when I get older.



excellent reason to put in snow melt.


----------



## in hot water (Sep 16, 2010)

At least 150 btu/ sq. ft for a class 1 snowmelt.  The class designates how much snow and how quickly you want to melt it.. 

 On helipads at hospitals, for example they would need to melt snow as fast as it falls, generally 200- 250 btu/ ft or more.

Anything less than 125 btu takes a long time to rev up, unless you idle the slab, which gets very energy intensive.

The slab only needs to be 34F to melt, generally a 80- 110 supply fluid.

Just as you do a heatload for a home you can do a load calc for snowmelt.  It's based on your location and the class of system you want.

All of the radiant manufacturers have snowmelt load program on their design software.  It take weather data from your location sizes the tube diameter, lengths and pump requirements.  40- 50% glycol, which takes more pump power and a way to isolate the snowmelt from the boiler fluid so you don't need to glycol the entire system.  Insulate under the slab of course, 2" like a heated radiant slab.

On some jobs we melted just the tire tracks or walk path, not the entire slab.

The state of Wisconsin banned residential snowmelts for awhile due to the large amount of gas they draw.  They may have lifted that ban.

In some resort areas it does pencil out when compared to the cost of hauling and dumping snow due to the tight building density and lack of snow storage space.

It would be tough to size a single boiler to cover your building heat and do much snow melting, you almost need to dedicate a boiler just to the melt load.

Tube the slab if you have the $$ to do it, and use it a s a DHW pre-heat "solar collector" in the summer.

hr


----------



## free75degrees (Sep 17, 2010)

I have thought about doing this.  I have an unpressurized storage tank and i was thinking I would add a coil to that and use it to feed the driveway loop.  This way I wouldn't have to worry about boiler return temps, and I'd also be able to use antifreeze without it mixing with the rest of my boiler water.  I'll definitely do the math first to make sure it wouldn't take too much extra wood though.


----------



## in hot water (Sep 17, 2010)

a cord of oak is about 27Mbtu.  Times the burn efficiency, maybe 70%?   That gets you down to 18.9Mbtu.  There are some efficiency loss through heat exchangers, storage, piping to and from, etc, take some % out for that. 

 So if you know how many BTU/hr you will dump out to the slab, keeping in mind the losses out at the slab, you can get an idea how much wood it takes to phase change snow to water.

And an excellent point above, about where the melt water goes.  You don't want an ice dam at the end of the slab that you can't drive or walk over.

Wind is tough on snowmelt slabs, it really scrubs away some energy.  Any type of edge insulation detail will help as will wind breaks.

hr


----------



## bulldogbones (Sep 18, 2010)

Thats some great reading guys The btu per sq ft was helpful, since I have 800 sq ft to heat (40'x20') so thats 800x150=120,000 btu's sooooooo I think this idea will get shelved, since I have an entire house to heat on a 140k btu boiler. And I think between the house and a driveway that would MAX the boiler out and I would be constantly feeding the boiler.


----------



## sgrenier35 (Sep 18, 2010)

You could always set up the zone so it only runs when the house heat is satisfied.  and or use it for a dump zone.


----------



## 4acrefarm (Sep 18, 2010)

I was thinking of a manual valve the diverts the solar antifreeze to the slab instead of the water tank. I would only use it occasionally for safety. The area is shaded on south and west sides and is our main entrance. I don't have solar yet but it's in the plans. I have a bunch of panels and I would combine the solar with wood with 1000 gal of storage.


----------



## bulldogbones (Sep 18, 2010)

sgrenier35 said:
			
		

> You could always set up the zone so it only runs when the house heat is satisfied.  and or use it for a dump zone.




Oh I agree but if I'm going to drop a little less then $800 on a heated driveway. I want it running all the time. The main reason I was entertaining the idea is because my wife just got a full time job 45min away 5days a week and since I work out of town that means she will have to keep the driveway clear so she can get in and out.


----------



## woodsmaster (Sep 18, 2010)

I looked into doing this and was told it had to be run all winter. I just wanted to use it on occasion, so that was the deal breaker for me.


----------



## 4acrefarm (Sep 20, 2010)

If it were a sidewalk could you do an insulated 3" slab? Maybe run fluid from solar panels to H/E then to sidewalk. I don't wory about tire traction, only foot traction.


----------



## woodsmaster (Sep 20, 2010)

sidewalks should be 4" and 4000 psi min.


----------



## Hiram Maxim (Sep 23, 2010)

My neighbor 5 houses down has a heated driveway.

Here is how his works. His floors are radiant heat, after they go up to the desired temp the system then drains into the tubes in the driveway on its way back to the boiler.

So the water is not heated for the driveway alone....  

Never any snow, never any ice!

Cheers,Hiram


----------



## 2.beans (Sep 29, 2010)

i have a heated patio and walkway. patio is 16x20 and the walkway is 4x60. just running that kills the boiler. its easier to shovel it rather cut wood for it. this year i was going to drain the water from the pex in my basement slab, fill it with antifreeze and circulate from the basement slab thru the the outside patio and walkway. my basement has 10 times the surface area as the the outside has so hopefully it will work. i dont see it keeping up in heavy snow but it should melt it off within a couple days. ive never used the basement heat so i wont miss it. im going to leave the circulator on 24/7 and if i ever i did want heat the basement im going to install the flat plate so i could by just shuttig the ball valves off for the outside.


----------

