Documentation of Calculations

Cutting Through the Noise

One of Zwell’s missions is to cut through all of the marketing-speak and misinformation around the clean energy space. We strive to provide you with accurate, fact-based estimates of the impact you’re likely to see in your home. In the interest of transparencey and shared knowledge, here is the underlying data used in all of our calculations on the site.

See Underlying Fuel & Energy Data

Zwell Calculations

CO₂ & Energy Savings by Category

Water Heating

Style	Model	Price	Energy Used	Estimated Yearly Energy Cost	Energy Label	CO₂/Year	CO₂/Year Equation
Electric Tank Water Heater	Rheem Performance 50 Gal.	$519	3,493 kWh/year	$419	Energy Guide Label	3,212 lbs	3,493 kWh x 0.92 lbs CO₂/kWh
Gas Tank Water Heater	Rheem Performance 50 Gal.	$699	269 therms/year	$293	Energy Guide Label	3,147 lbs	269 therms x 11.7 lbs CO₂/therm
Gas Tankless Water Heater	Rheem Performance Platinum 9.5 GPM	$1,349	182 therms/year	$198	Energy Guide Label	2,129 lbs	182 therms x 11.7 lbs CO₂/therm
Hybrid Heat Pump Water Heater	Rheem Performance Platinum 50 Gal.	$1,199	866 kWh/year	$104	Energy Guide Label	796 lbs	866 kWh x 0.92 lbs CO₂/kWh

Going for Zero, Episode 1

New Hybrid Water Heater & CO₂

Rheem Performance Platinum 80 Gal.

Estimated energy use: 1,240 kWh/year (Energy Guide Label)

CO2 Calculation: 1240 kWh/year * 0.92 lbs CO2/kWh * 0.66 Washington State’s Relative Carbon Intensity of Energy Generated = 753 lbs CO2/year

Cost Calculation: 1,240 kWh/year * $0.08 Avg. Washington State Cost per kWh = $99.20/year

Old Gas Water Heater & CO₂

Rheem Gas Tank Water Heater

Estimated energy use: 269 therms (Energy Guide Label)

CO2 Calculation: 269 therms/year * 11.7 lbs CO2/therm = 3,147 lbs CO2/year

Cost Calculation: 269 therms/year * $1.60/therm = $430.40/year