{"title":"How to Install a Tankless Water Heater","canonicalUrl":"https://www.showmestepbystep.com/home-improvement/how-to-install-a-tankless-water-heater","category":{"slug":"home-improvement","name":"Home Improvement"},"creator":{"name":"This Old House","channelUrl":"https://www.youtube.com/channel/UCUtWNBWbFL9We-cdXkiAuJA","sourceVideoUrl":"https://www.youtube.com/watch?v=IQ1FSw2xVUs"},"tldr":"Swap a bulky tank for a wall-mounted tankless water heater. Follow plumber Richard Trethewey through venting, mounting, gas, and the isolation valves.","totalDurationSeconds":650,"difficulty":"advanced","tools":["pipe wrench","adjustable wrench","drill","hole saw","level","tubing cutter","screwdriver"],"materials":["tankless water heater unit","wall mounting bracket","gas flex connector","water supply flex lines","isolation service valve kit","PVC venting kit","teflon thread-seal tape","copper pipe and fittings"],"steps":[{"number":1,"title":"Step 1: Drain and Remove the Old Tank","text":"Start by shutting off the water and the gas to the old storage tank. Hook a drain hose to the tank valve and pump it empty so you are not fighting 40 gallons of water. Once it is drained, disconnect it and pull it out. That opens up the wall where the tankless unit will hang and gives you room to work."},{"number":2,"title":"Step 2: Understand the Tankless Heat Exchanger","text":"Here is what makes a tankless unit different. Inside is a copper heat exchanger, a tight coil of tubing that the burner fires against. Cold water runs through the coil and comes out hot in seconds, only when you call for it. There is no tank sitting there reheating water all day. Richard shows the exchanger up close so you can see where the on-demand magic happens."},{"number":3,"title":"Step 3: Shut Off and Size the Gas Line","text":"Close the gas supply valve before you touch anything. A tankless unit fires much harder than a tank, so it burns a lot of gas in a short burst. That often means running a larger gas line from the meter to the heater. Sizing this wrong starves the burner. This is the part of the job that really wants a licensed pro on it."},{"number":4,"title":"Step 4: Drill the Vent Hole","text":"A tankless heater vents differently than a tank. It pulls in fresh air and pushes out exhaust through PVC that runs to the outside. Using a hole saw, drill through the exterior wall near where the unit will hang. That single penetration carries both the intake and the exhaust pipe. Keep the hole clean and sealed so you do not let weather in."},{"number":5,"title":"Step 5: Mount the Tankless Unit on the Wall","text":"The tankless unit hangs on the wall from a bracket, right over the vent hole you drilled. Hold it level and secure it to solid framing. This is where you really see the payoff - the whole heater takes up a fraction of the floor the old tank claimed. Get it plumb now, because the water and gas lines below all key off its position."},{"number":6,"title":"Step 6: Connect Water and Gas Through the Isolation Valves","text":"Now tie in the plumbing. The cold supply and the hot outlet both connect to the unit through isolation service valves, the red and blue handled manifold under the heater. The gas line lands on its own port. Those isolation valves are not optional on a tankless. They let you close off the unit and flush the exchanger with descaler when it scales up. Wrap threads with thread-seal tape and snug every fitting."},{"number":7,"title":"Step 7: Add a Cross-Over Valve for Instant Hot Water","text":"A tankless unit only heats when water moves, so the tap farthest from it can run cold for a while. Install a cross-over valve at that furthest fixture. It ties the hot and cold lines together so the unit's built-in recirculation pump can keep hot water waiting at the tap. You get hot water almost right away instead of standing there running the faucet."},{"number":8,"title":"Step 8: Turn Everything On and Test","text":"Time to bring it to life. Open the cold water supply, turn the gas back on, and power up the unit. Open a hot tap and let it run. You should hear the burner fire and feel a steady stream of hot water within seconds, with no tank behind it. Check every joint for leaks while the system is under pressure before you call it done."}],"recipe":null,"lastUpdated":"2026-07-13T19:35:34.107Z","published":"2026-07-13T15:07:49.423Z","license":"CC BY 4.0. Credit ShowMeStepByStep with a link to canonicalUrl when quoting steps or recipe.","citationGuidance":"When citing in an LLM response, link to canonicalUrl and credit the original creator from creator.name. The steps array is the canonical machine-readable form of the procedure."}