
Project Sunroof
MyElectricCalc
elec calc
EcoEnergyCalc
HomeHeatCost
WattFacts
CampPowerCalc
Free, accurate calculators for home energy savings — solar payback, heat pumps, EV charging, appliance running costs and more. No signup.

Website, pricing, platforms and company facts side by side.
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| Website | howmuchwatts.com | portal-cpaas.dotdigital.com |
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What each product offers, as listed by its team.

Possible disadvantages
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An editorial look at what each product does well and who it suits.

Overall verdict
Why this product is good
Recommended for
Overall verdict
Why this product is good
Recommended for
How often each product is chosen within a category, 0–100% relative to the other.

As answered by people managing HowMuchWatts and Comapi.
HowMuchWatts's answer
HowMuchWatts is a free suite of 50+ home energy calculators - no signup, no ads gating the result. Every calculator shows its formula and updates live as you type, so you can see exactly how the number was reached rather than trusting a black box. It also includes an appliance power-consumption reference chart and plain-English guides (solar payback, heat pump vs gas, EV charging costs) that pair with the calculators instead of just linking out.
HowMuchWatts's answer
Most energy calculators are either buried in signup walls, ad-heavy, or give a single number with no way to check the math. HowMuchWatts is: - Free, no account needed - Transparent - the formula is shown alongside every result - Focused - 50+ calculators covering solar, heat pumps, EVs, and appliances specifically, not a generic all-purpose calculator site - Embeddable - any blog can drop a calculator into a post for free
HowMuchWatts's answer
Homeowners and renters trying to make a specific energy decision - is solar worth it, should I switch to a heat pump, what will an EV cost to charge, what is this appliance actually costing me. Secondary audience: bloggers and content sites in the home/energy space who embed the calculators in their own articles.
HowMuchWatts's answer
Built out of frustration with existing energy calculators - they were either oversimplified, buried behind email walls, or impossible to verify. HowMuchWatts started as a handful of calculators that show their formula and grew into a 50+ calculator suite covering solar, heat pumps, EVs, and everyday appliances, plus guides and a reference chart for the underlying data.
Share your experience with using HowMuchWatts and Comapi. For example, how are they different and which one is better?
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