Hot water systems are constantly evolving. In this video, Matt Risinger interviews Gary Klein, an expert in hot water systems and system efficiency. Risinger asks Klein to give the one-minute version on why it's important to think about hot-water layouts.Hot water layouts are important because customers don't like waiting for hot water to arrive. As a builder it's your job to make sure they are happy. Klein asks builders to answer one question - how long do you want your customers to wait for hot water. How they answer allows Klein to help design the plumbing to meet that goal.The average house in America is waiting between one and two minutes and is wasting between a gallon and two gallons down the drain. Klein's goal is to waste no more than one cup and five seconds before the water gets there. He also admits it's not always easy to get there. He sets realistic expectations and works with the building team, the builder, the architect, plumber, other subs to make it work. The first steps to get there based on how long they want to wait include The response tells Klein how long to make the branch lines—the twigs to serve each fixture, hot or cold. Once you know the answer to twig length, the plumbing can be designed to connect all of the bits up to have an efficient design. Most floor plans require a circulation loop and Klein prefers specified demand activated loops as the most energy efficient way to prime lines with hot water. If you don't want a demand system, or don't have the budget for it, the lesser ground is to put the plumbing in to be retrofit-ready. The marginal cost in virtually every job is the cost of pump and controls. If there isn't the money at the time of construction, build it so that it can be fixed for a few hundred dollars when they can afford it. It's also important to consider the layout of the house to get compact plumbing cores with the water heater in the center of the core, that would be best. It actually costs less to build a better house in this regard.Klein reviews manifold systems—the trick is to imagine there is a one-quart plumbing system so that all paths from the water heater to fixtures is no more than one quart long. Risinger asks Klein for his favorite configurations for efficiency. Customers want hot water now and to never run out, and a parental control switch for their teenagers. To never run out requires a certain heat rate and volume. Small volumes as in traditional tankless requires heavy modulations to get low flows and temperature rise. It's necessary to reduce the complexity of controls and increase capacity. Hot water for one shower typically takes 60,000 to 80,000 BTUs per hour. The model used most is 100,000 BTUs and 50-gallons. If you want efficiency, make sure to flush the system every 12 months. There are also interesting electric solutions from an efficiency point of view is to take a heat pump water heater, an air source heat pump that's appropriate for your climate and run the heat pump only monitor the output. You would effectively double the volume of output. The heat pump does the bulk of the work. Klein provides descriptions of how this would work with an electric system and with a gas system in the video—offering suggestions seldom considered.