About 150 people a day sign up to Cool Calc, a U.S. app that estimates how much heat a home loses in cold weather, and just over a third of the new users are private homeowners rather than tradespeople, the BBC reported. Founder and chief executive Bill Fiore said homeowners want to run the numbers themselves instead of taking an installer at their word. A heat-loss figure, usually measured in watts and worked out room by room, is especially important for a heat pump, which is sized fairly precisely to that estimate. If the calculation is off, the system can be underpowered, or oversized and wasteful. Fiore also warned that people are turning to AI chatbots and "getting a lot of misinformation because it's not backed by anything credible." Cool Calc is planning to integrate with those chatbots to try to improve the advice they give.
Kevin Kircher of Purdue University and colleagues, in a study that has not yet been published, examined heat-loss calculations that tradespeople provided to about 75 U.S. homeowners. "The heat loss calculations often led to overestimating the design heat loads by a factor of two or more," Kircher said, which would produce oversized systems that use much more power than necessary. Some people reported being charged more than $1,000, and in one case as much as $2,500, just for a survey. Dan Dempsey, a former senior engineering fellow who took part in the study, said oversized equipment tends to cycle on and off quickly, so rooms swing around the target temperature instead of holding it. In retirement he has made a hobby of downloading smart-thermostat data from friends' and family's homes.
Free or partly free tools include Cool Calc and AutoHVAC in the United States and Heatpunk in the United Kingdom, which lets users draw a floor plan and, its operator Midsummer Energy noted, also suggests models the company sells. Dwellow, a U.K. installer, recently launched its own estimator; co-founder Ian Mclaren said a homeowner "self survey" could turn a professional visit into a half-hour check rather than a start-from-scratch inspection. Maurizio Sibilla of the University of the West of England in Bristol argued that the real fix is better installer practice and clearer evidence, "not expecting homeowners to do the engineering themselves."
Adam Chapman of the Heat Geek training network was more sceptical, saying only careful surveys catch hidden gaps such as windows that were never foam-insulated or cavity walls a homeowner thought had been filled. The verified tension is between newly empowered homeowners, documented oversizing, and engineers who say the mistakes that matter are often the ones you cannot see from an app.