Installing a new water heater sounds easy enough until your garage floods, your water turns ice cold, or your ceiling mysteriously starts dripping. That “quick weekend project” can go sideways fast if it’s rushed, winged, or inspired by a little too much confidence and a YouTube tutorial from 2013.
Truth is, this isn’t just plug-it-in-and-hope-for-the-best territory. One small slip—wrong size, bad connection, sloppy venting, and suddenly you’re dealing with more than just cold showers.
Whether you’re swapping out a tired old tank or installing a brand-new system, it pays to know what not to do. Here’s a look at the most common mistakes plumbers run into during water heater installations and why skipping the small stuff can turn into a very big deal.
Skipping the Permit or Ignoring Local Code
One of the first things that gets overlooked is paperwork. In many areas, installing a water heater without a permit isn’t just risky—it’s illegal. Local plumbing codes exist for a reason, especially when gas lines, pressure systems, and venting are involved. Failing to follow the code could cost you later, either through fines, insurance issues, or safety problems.
Choosing the Wrong Size Heater
Too small, and someone’s getting stuck with cold showers. Too big, and you’re wasting money heating water you’re not using. Sizing isn’t guesswork—it depends on how many people live in the house, how often you use hot water, and what kind of fixtures and appliances you have. A lot of folks just replace whatever size was there before without checking if it was right to begin with.
Improper Venting for Gas Water Heaters
Gas water heaters need safe, efficient venting to remove combustion gases. If the vent is the wrong size, slopes incorrectly, or uses the wrong materials, you could end up with dangerous fumes backing into the house. Proper venting isn’t just a technical detail—it’s a safety essential.
Poor Location and Clearance
Where you place a water heater affects how it performs and how long it lasts. It needs to be somewhere with enough space around it for air flow, maintenance, and safe operation. Squeezing it into a tight corner or installing it too close to walls can create bigger problems down the line.
Leaving Out the Expansion Tank (When It’s Needed)
Many homes—especially those with closed-loop systems—need an expansion tank to handle the pressure created when water heats up. Without it, the excess pressure can damage valves, shorten the heater’s lifespan, or stress the plumbing system. Whether or not your setup needs one depends on your system’s design, and it’s not always easy to tell without an inspection.
Using the Wrong Materials for Connections
This is one of the more frustrating ones. We’ve seen plastic flex lines where there should’ve been copper, mismatched pipe sizes forced together, and gas fittings that didn’t seal properly. Just because something “fits” doesn’t mean it’s the right part for the job. The wrong materials may hold for a little while, but eventually they fail, and usually when it’s least convenient.
Don’t Cut Corners with Installation
A new water heater should give you years of trouble-free use. But that only happens if it’s installed correctly. It’s easy to overlook things like size, venting, pressure relief, and material quality, but those are the details that matter.
If you want to avoid dealing with leaks, bad installs, or code issues down the road, get it done right from the start.
Cisneros Brothers Plumbing, Septic, Restoration & Flood Services handles water heater installations the way they should be done: by the book, no shortcuts, no guesswork. When you’re ready for a proper install, we’re ready to get it done right. Just give us a call.
With Isaac Cisneros leading as President of Marketing, the company’s reach continues to expand, strengthening its presence in both the industry and the community.
