As it rolls out new consumer Wi-Fi routers that support a private network for the high-speed access customer and also create a separate public Wi-Fi node, there will be cost implications for consumers, much as use of TV set-top boxes draws energy from the consumer’s home account.

Comcast (News - Alert) public Wi-Fi features are being used to create a nationwide Wi-Fi service that can be used by non-Comcast customers, costing $3 an hour, $8 a day or $20 a week.

According to a test conducted by Speedify, a user in Philadelphia would pay for between $15 and $23 a year in additional electricity costs to support Comcast’s public Wi-Fi hotspot feature.

But Comcast thinks electrical consumption would be lower than that. The Speedify test apparently used a business grade router and was an older model that does not reflect the current power consumption of a consumer router.

In fact, Comcast says the incremental energy consumption should hardly be discernible, and is imposes negligible additional energy draw.

Consumers also have the ability to turn off the public Wi-Fi feature, so the issue might not be nearly as big as first seemed to be the case.

But Comcast has said it plans to activate eight million of the new routers by the end of 2014.

What is not yet so clear is how the new network might actually work, in residential areas outside of urban cores, where Wi-Fi signals do not necessarily reach all the way out into the street. It seems unlikely too many people will use the “public” access in residential areas, for that reason.

More significant are potential usage scenarios in denser urban areas where the public signals might actually reach far enough outside consumer homes to be usable by the public at large.

The broader issue is not new. Cable TV set-top boxes, for example, consume rather large amounts of energy even when turned off, about $8 a month or $96 a year for consumers in Southern California, for example.

The difference is that that power consumption is the result of a consumer choosing to buy a service that requires a device that draws power. The Comcast public W-Fi network does not directly benefit the customer supplying the electrical power.

To be sure, improvements are being made. But a 2011 study found that a single a high-definition cable or satellite set-top box, equipped with a high-definition digital video recorder feature uses up 446 kilowatt hours per year.

That's more than a new Energy Star rated 21 cubic-foot refrigerator, which uses 415 kWh per year, according to the Natural Resources Defense Council data. And about 66 percent of the energy consumed occurs when consumers are not actually watching TV or recording content.