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.
The average cost for gas water heating units is $850. That will buy you a decent water heater that is rated for 12 years. These, too, can be found for cheaper than that price. You may find a 3 year rated water heater for about $350. Quality units can cost $1,000 to $1,400.