HomeAdvisor’s Water Heater Cost Guide lists pricesociated with installing or replacing a water heater including labor and materials, as reported by HomeAdvisor customers..HomeAdvisor’s Tankless Water Heater Cost Guide gives the average prices for electric and gas systems, installation, replacement, and maintenance as well as cost comparisons fornds like Rinnai, AO Smith and Polaris..How much replacing a water heater should cost. Average costs and comments from CostHelper’s team of professional journalists and community of users. With all needed parts and labor, hiring a plumber to install a traditional gas water heater costs $ $, or more, depending on capacity with gallons the most common sizes length of .How to Install a Tankless Water Heater. You will thank yourself a million times over for choosing tankless water heating. Be aware that there will be a slight delay for the water to arrive at your fixtures and that the money saved .