The Smart-Thermostat Payback

Ada re-derives this chapter’s own numbers step by step, at full precision

ADA · CALCULATION AUDIT

The Smart-Thermostat Payback

The chapter’s human-centered example is a $250 smart thermostat in a home that spends $3,900 a year on heating and cooling and trims that bill by 30%. It argues the device sells itself because the payback lands in months, not years. This audit walks the payback line by line — annual saving, monthly saving, then months to break even — to ask exactly how fast a $250 device pays for itself.

Companion to the chapter What IoT Delivers — every number here comes from that chapter.

Ada: The chapter claims a $250 smart thermostat pays for itself in about 2.6 months for a home that spends $3,900 a year on heating and cooling and cuts that bill by 30%. Let me walk the payback all the way through.

• Annual savings: 3900 x 0.30 = 1170 dollars
• Monthly savings: 1170 / 12 = 97.50 dollars
• Payback period: 250 / 97.50 = 2.564 months, which rounds to 2.6 months.

A payback measured in weeks rather than years is exactly why this product sells itself — but the number is only as trustworthy as the 30% savings assumption underneath it, so the payback claim should always be quoted together with the efficiency figure it depends on.

Every number above is taken from the chapter’s own material and re-derived step by step.