I'm designing a silicone rubber heating pad with the intent to melt excess snow and ice from the gutters of homes to prevent ice dam formation. I'm trying to get professional opinions on what size heating resistance wire I should buy. The heating pad will be 2ft long.

 

Without more information, I don't know what you expect us to do. You might want to tell us what temperature range you had in mind, how much wire you planned to use per two foot section, and most importantly how you planned to deliver power to the wire. FWIW I don't see this as a problem that is in desperate need of a solution.

http://www.jacobs-online.biz/nichrome/NichromeCalc.html

For example 2 feet of 13 ga. wire at 1.6 volts will get you 200° F. I don't know if that is a helpful data point or not -- you tell me. 200°F is not something I'd want to put my lips on!

 

It would just need to raise temperature slightly above freezing - max temp of 50 degrees F, 8-10ft. per 2ft. of pad, and it will be powered by a home outlet. To go more in detail, the pad will be connected to an Arduino and temperature sensor that detects when temperature hits below freezing (32F) and tells the pad to turn on.

 

It would just need to raise temperature slightly above freezing - max temp of 50 degrees F, 8-10ft. per 2ft. of pad, and it will be powered by a home outlet. To go more in detail, the pad will be connected to an Arduino and temperature sensor that detects when temperature hits below freezing (32F) and tells the pad to turn on.

What makes you think a controllable 50° F is possible with nichrome wire? If you look at the calculator I showed you, 200°F is bottom end of the range and 2600°F is the top of the range. I hope you are not intending to run the nichrome wire directly from the mains. That will probably get this topic banned. How do you plan to control the AC voltage to limit the temperature rise in the wire to just 50°F?

 

We have another temperature sensor placed on the pad that detects when it reaches our desired temperature (hypothetically 50°F) and once it does the pad will turn off. It will fluctuate maintain our desired temperature.

 

Take a look at the existing commercial products. For instance this:

I'm pretty sure I've seen the type of product you described - a big heating pad - but I couldn't find an example.

I think from studying how those products work, you'll get a better idea of what you need. I'd look hard at watts per linear foot of cable, and how (and if) they achieve control. (It may just be on/off depending on ambient temperature).

I recently fixed the seat warmers in my car. The heating wire had frayed and eventually burned out in one section. Those heating elements are controlled by using a sensor that looks at the temperature in just one spot along the wire. It prevents that spot from getting too hot. Since the wire is uniform, it works for the whole seat. The 'wire' is actually a cable with many parallel strands.

There are probably better materials to consider than nichrome wire.

 

This is the time of the year when Home Improvement stores like Lowes and Home Depot in the US are dumping their winter stock of gutter and roof heaters.
https://www.lowes.com/search?searchTerm=gutter+heaters
http://www.homedepot.com/s/gutter%20heaters?NCNI-5

Next month this stuff will be really inexpensive.

Ron