Serpentine cable footage, clips, GFCI circuits and cost for ice-dam heat cable.
Estimates are planning aids, not a professional quote. Double-check quantities and product coverage — and any local code or permit requirements — before you buy.
⚠ Heat cable belongs on a dedicated GFCI-protected circuit run from the panel — never share it with another outdoor circuit, and have a licensed electrician make the panel connection if you're not comfortable with it.
| Electrical | $418–$566 |
| Roofing | $26–$35 |
| Total | $444–$601 |
Excludes tools, delivery, tax and permit fees. Labor not included — this is a DIY materials estimate.
These are affiliate links: we may earn a commission if you buy through them, at no extra cost to you. It never changes what the calculator recommends — the shopping list comes from your dimensions, not from what pays.
About this calculator
Give the Roof Heat Cable Calculator your eave length, the triangle height the zigzag climbs onto the shingles, and how many downspouts and valleys need their own run, and it works out the real serpentine footage — not the straight eave length, which badly undercounts a triangle pattern. A 40 ft eave at a 15 in triangle and 12 in spacing needs well over 100 ft of cable once the zigzag is accounted for.
From there it sizes roof clips and gutter hangers, splits the total wattage across dedicated GFCI circuits using the 80%-continuous-load rule, and prices the breaker, receptacle or disconnect, and a thermostat or moisture-sensing controller. Choose self-regulating or constant-wattage cable and 120V or 240V service, and every line reprices instantly, along with a full cost estimate. It also warns when a shallow triangle height won't reach a roof's historic ice-dam line, though it stops at the circuit itself and doesn't size the feeder run back to your electrical panel.
Step by step
A step-by-step walkthrough to go with your plan above. Follow the product instructions and any local code or permit requirements as you work.
Measure the eave run, count downspouts and valleys, and use the calculator to get the real serpentine footage, clip count and circuit sizing before you buy anything.
Check that a dedicated GFCI circuit of the right amperage and voltage is available at the panel — plan on a licensed electrician for the panel connection if you're running new 240V service.
Slide a plastic clip under the shingle tab at each point where the zigzag pattern is going to peak, spaced evenly along the whole eave run.
Route the cable up from the gutter edge to the clip height and back down at your set spacing, snapping it into each clip so the triangle pattern holds its shape without sagging.
Lay the cable along the gutter channel itself and clip it in place with gutter hangers so it doesn't shift or lift out in wind.
Drop a cable leg down through each downspout that could ice shut, and route a separate run up each valley to above where snow historically dams — these are separate strands from the eave zigzag, not extensions of it.
Splice the cold lead into the heated cable with the factory connection kit, cap the far end with an end seal, and land the lead on the GFCI breaker or receptacle.
Mount the thermostat or moisture sensor where it reads outdoor conditions accurately, power up the circuit, and confirm the whole run gets warm evenly before the first hard freeze.
Equip the job
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Decks & Structures
Answers
More than the straight eave length. The cable is woven in a triangle (zigzag) pattern that climbs from the gutter edge up onto the shingles and back down at a set spacing, so it covers the whole band where ice dams actually form rather than just the edge. A 40 ft eave at a 15-inch triangle height and 12-inch spacing needs a bit over 100 feet of cable — this calculator does that geometry for your exact eave length, triangle height and spacing, then adds the downspout legs and valley runs on top.
Self-regulating cable senses its own temperature along its length and backs off output where it's warmer, so it can cross itself in the gutter, run through a downspout, and generally last longer without burning out. Constant-wattage tape puts out the same heat everywhere, can't touch itself without overheating, and is cheaper up front — fine for a short, simple eave run, but self-regulating is the standard choice for anything with valleys, downspouts, or a run that overlaps itself.
Yes. Heat cable should run on its own dedicated GFCI-protected circuit, sized so the calculated wattage stays under 80% of the breaker's rating — the standard continuous-load rule. A single run on one house rarely trips a 20A circuit, but a large or multi-valley roof can add up to more amperage than one circuit should carry, which is when the calculator splits it across two or more circuits instead of overloading one.
Anywhere meltwater can refreeze before it clears the roof: down through every downspout that would otherwise ice shut, and up every valley to above the point where snow typically dams against it. Skipping the downspouts is the single most common reason a heat-cable system still backs water up — the eaves stay clear but the downspout freezes solid and the water has nowhere to go.
A basic freeze thermostat energizes the cable below a set temperature (commonly around 38°F) and is the standard, affordable choice. A moisture-and-temperature sensing controller only turns the cable on when it's both cold and actually wet or icing, which cuts electricity use significantly on a long, dry cold snap — it costs more up front but pays that back over several winters on a system that runs all season.
It manages them, but it isn't a substitute for fixing why they form. Ice dams happen when a warm roof deck (from poor attic insulation or ventilation) melts snow that refreezes at the cold eave. Heat cable keeps a channel open so meltwater has somewhere to drain, but on a roof that dams badly every year, check attic air sealing and soffit/ridge ventilation first — cable alone treats the symptom every single winter instead of the cause.