In the winter, should deicing cable be left on 24/7 when temperature are below freezing?

 

The cables are there to prevent ice dams. They should not be left on 24 hours a day and usually aren't used above like 40° weather. The cables are expensive to run so use needs to be frugal.

Everyone has their own idea about how to use the cables. Each application is different and is affected by the pitch of the roof, leakage of hot air into attic, outside temps, thickness of snow/ice. I'll usually run mine for approx two days after a fairly good snow storm. I don't use the cables for every storm. If the snow lingers and the temps are real cold.... I may run them in the day only when the sun melts the snow.

Most roofs don't need ice melt cables. They are predominately for shallow pitched roofs. I have an additional two pieces of cable in gutters and downspouts were I have a rooftop that overlooks a driveway and where the gutters and leaders freeze due to being on the cold side of the house.

 

The gutters seem to get full of ice here all season as it rarely gets above 0 Celsius.
Problem is the cable doesn't really melt the ice in the gutters, it just makes a path through the ice so if any meltwater comes off it has somewhere to go.
Why only run it after a storm? Especially if the snow is on the roof all winter, it seems to melt from heating and fire user in the house...

 

Shouldn't the gutters be free from ice completely though?

 

I had a home in MN and ran it off a couple of cable timers that I could put to sleep or over-ride if the conditions were bad for ice build-up. No sense in 24x7 operation. You just need to create a drainage path that can work well in spite of a small cosmetic surface snow level.

Cold weather was not a problem because snow (only 45"-90" there per year) were followed by cold and clear weather with a lot of sun. The radiant solar heat does a lot of good (even on cloudy days) to burn through. Snow will melt below the surface when in sun's radient rays go through the clouds and snow and warm the roofing surface.

Valleys were a problem area, but they are somewhat predictable AND are the main source of drainage to downspouts. My main resource was a long string of tape in a couple of valleys with the tail end running down the downspout to provide drainage. That is the main item and the ugly zig-zag on the eaves were used rarely. - The eaves always were drained because of the RADIANT solar heat that even works at below 0F.

If you have different weather sequences (warmer and heavy clouds), that may not apply.

Dick

 

What happens here is that meltwater always comes off the roof and then freezes again in the gutter eventually overflowing and creating icicles.
I'm trying to stop that from happening and because it's s metal roof, it seems to melt readily anytime the heating or fireplaces are used.
Cable is only in the gutter at the moment.

 

Hi qwerty,
I'm in Maine so VERY familiar with ice from snow melt. As others have said, each home and location will perform differently, but gutters in a northern climate are almost impossible, Most homes in my area, central Maine, exclude them. I even considered removable ones so I could have them for 8 months of the year and never have ice in them the other 4 (they would be in the garage).

Number one, you can't leave the snow on the roof. Snow melt can come from heat loss (or air leakage) into the attic or solar conditions that shine right through the snow and warm the roof.

Number two, there is little you can do about the sun (until you replace the roof), but eliminating heat loss and air leakage into the attic is a must. Combined with good ventilation the bottom of the roof never gets warm enough (when freezing outside) to melt the bottom layer of snow.

Get a snow rake, and review attic ventilation, insulation, and air sealing.

Bud

 

Why not leave snow on the roof? It's a metal roof and we have snow barriers as well, which actually keep the snow Fortin falling off avalanche style.

 

Snow acts as an insulating blanket which allows the heat that escapes into the attic to melt the bottom layer. That insulating layer continues to protect the resulting water from freezing until it exits the bottom edge. There it freezes in layers until it backs up the water and eventually forces it under the shingles. With your metal roof, there are different styles, but how far the ice dam can back the water up before it leaks varies.

Removing the snow eliminates the source of water and keeps the roof cold.

Bud