To make sure you're not testing too early, assume the sperm had very long lives (5 days is considered a very long sperm life) and that conception occurred then. Then allow 14 days for the embryo to implant and develop enough hCG to show up on a pregnancy test (96% of pregnant women will test positive by then.)
A gas water heater will recover in half the time of an electric unit. A 40-gallon gas water heater can recover in about an hour. Recovery for a 40-gallon electric water heater takes about two hours.
Requirements for water heaters to qualify for Energy Star. Gas storage type energy efficient water heater should have EF (energy factor) 0.67 (used to be 0.62) or higher, and the First Hour Rating at least 67 gallons per hour. See the requirements here. Gas tankless water heater requirement for EF is 0.82 or higher and 2.5 gpm over 109 F temperature rise or higher.