Compare three scenarios
Smart thermostat · calculator
A national average does not pay your utility bill. It is more useful to see what a few plausible savings scenarios would mean against your own annual heating and cooling spend.
System compatibility and the way you already manage temperature matter as much as the thermostat itself.
ENERGY STAR says certified smart thermostats save about 8% of heating and cooling bills on average. That is a useful reference point, not a promise. The underlying evidence is based on real U.S. homes, and outcomes vary with climate, comfort preferences, occupancy, HVAC equipment and how the previous thermostat was used.
The calculator below therefore does not tell you that you “will save 8%.” It shows what three scenarios would look like using your own cost base.
Compare three scenariosAnnual heating + cooling spend (€)Thermostat + installation cost (€)Calculatefunction euro(n){return new Intl.NumberFormat('en',{style:'currency',currency:'EUR',maximumFractionDigits:0}).format(n)}function calc(){const s=Math.max(0,Number(document.getElementById('spend').value)||0),c=Math.max(0,Number(document.getElementById('cost').value)||0);const rates=[['Cautious scenario',.04],['ENERGY STAR average',.08],['Higher scenario',.12]];let h='<table><thead><tr><th>Scenario<th>Rate<th>Annual savings<th>Simple payback<tbody>';for(const [name,r] of rates){const save=s*r,p=save>0?c/save:null;h+=`<tr><td>${name}<td>${Math.round(r*100)}%<td>${euro(save)}<td>${p===null?'—':p.toFixed(1)+' yr'}`}h+='<p class="meta">8% is the published ENERGY STAR average. The 4% and 12% values are comparison bounds chosen for this calculator, not sourced predictions.';document.getElementById('result').innerHTML=h}calc();
What number should you enter?Use only the part of your annual energy spend that actually belongs to heating and cooling. A total electricity bill may also include lighting, appliances, cooking, hot water and other loads. Feeding the full bill into the calculator can overstate the potential savings.If you do not know the exact amount, compare a reasonable low and high estimate instead of pretending one uncertain number is precise.
Why your result may differ from the averageYou already manage temperature efficiently. A well-programmed existing thermostat may leave less room for improvement.Your climate is different. A mild climate may leave a smaller heating/cooling base to save against.Your home is rarely empty. Automatic setbacks have different value in an empty weekday home and a home occupied all day.Your system has specific controls. Heat pumps, boilers, multi-zone systems and other setups can require different control strategies and compatibility checks.Convenience may be the main benefit. Remote control, schedules and visibility may matter even when the financial payback is modest.
Before buyingConfirm that the exact thermostat is compatible with your heating/cooling system and wiring.Check whether installation can be done safely under the product instructions or requires a qualified technician.Include the full purchase cost: device, installation and any extra hardware.Run at least a cautious and an average scenario.Check local rebates or incentives separately; they change and are not built into this calculator.A useful rule of thumb: if the purchase only looks attractive in the highest scenario, treat savings as an uncertain bonus rather than the whole reason to buy.
SourcesENERGY STAR — Smart Thermostat FAQENERGY STAR — Smart Thermostats Key Product CriteriaChecked September 7, 2026. ENERGY STAR evidence is U.S.-based and is not a guaranteed local result for any individual home.
