Comcast has been pushing new Xfinity WiFi routers onto subscribers that broadcast a public WiFi network in addition to their home Internet connection. These Xfinity WiFi Hotspots will together create a giant wireless network that Comcast is already selling access to for $19.95 per week to non-Xfinity customers (see pricing at bottom of http://wifi.comcast.com/). As a bandwidth-obsessed engineer, I wanted to understand exactly what Comcast is doing here. Despite their claims that these routers cost subscribers nothing extra, we actually measured the power consumption on the business router they sent us and were surprised by the results. Based on our tests, we expect that by the time they roll it out to all of their subscribers, Comcast will be pushing tens of millions of dollars per month of the electricity bills needed to run their nationwide public WiFi network onto consumers.

Comcast sent us the standard business Xfinity Hotspot setup for use in our office (this is different than the residential equipment). This includes a Cisco DPC3008 cable modem and BelAir 20E Wi-Fi router, which broadcasts the Xfinity public hotspot. It’s worth noting that this is totally separate from the Netgear CG3000DCR cable modem that supplies our office Internet gateway. We started testing by plugging both devices into a power strip, which was being monitored by a Kill-A-Watt power meter. First we tested the devices idle to get a control for the experiment. We turned on the Xfinity public hotspot and connected it to the Internet, but no one was on it. After getting some consistent data, we then connected two Windows laptops to the Xfinity hotspot, one watching Netflix and the other downloading files. You could immediately see the difference in the power meter, as the devices jumped from 0.14 Amps when idle, up to 0.22 Amps when actually being used. To translate this into dollars and cents, we used the average cost of power here in the Mid-Atlantic, which is $0.162 per KWh.

	Amps	Vrms	PF	KWh	KWh / year	Cost in Middle Atlantic (2013)
Idle	0.14	122	0.62	0.0105896	92.764896	$14.99
Under Load	0.22	122	0.6	0.016104	141.07104	$22.80

So, here’s what it actually costs you to host a “free” Xfinity Hotspot: up to $22.80 per year for those of us here in Philadelphia, or $1.90 per month.