DIY Natural Gas Hot Water Tank Replacement

I came downstairs and found a pond of water on the floor. I knew this meant there was no hope for the current tank and needed to be replaced.

The first question: Can a weekend DIYer complete this task? Of course you can!

Going back to one of my other posts DIY Barn Doors Step-by-Step, it was a blessing that I thought ahead with the bypass sliding doors, otherwise this would have been a huge pain to complete.

Step 1: Shut Off the Water

After seeing the water on the ground I instantly turned the water off at the shutoff that was located on the input line to the water tank.

Step 2: Drain the Tank

Knowing that the water was going to continue to leak all over until the tank was empty, I grabbed the garden hose, connected it to the tank drain line, and emptied it into the sump crock.

Once the tank was partially emptied I opened the pressure relief valve to allow the tank to drain faster.

Step 3: Decide on Replacement

That’s when I asked myself the question, do I call someone or do it myself.

I absolutely hate paying people to do work that I am capable of doing so I decided I would tackle this.

I looked online at Lowes and Home Depot and found a similar 40 gallon tank with power vent that had good reviews and in stock at a local store. Lowes won and I picked up this AO Smith 40 gallon natural gas power vent unit (Lowes article number 816135).

Step 4: Bring the New Tank Home

I hopped in the truck and went to pick it up, grabbing the 3/4″ threaded female PEX adapters that thread on to the new tank that I needed that I didnt have as the old ones had signs of rust and corrosion after 12 years.

Once home I had some help getting the new tank down to the basement. Having a hand cart with some ratchet straps made this much easier! The tank weighs about 175lbs empty. Not too bad, but not too light either.

By this time the old tank was pretty empty but I left the garden hose attached until I could tip the tank and drain it a bit more.

Step 5: Disconnect the Old Tank

I started with the old tank unplugging the power vent which stopped the power to the control unit as well.

I then turned off the gas shutoff valve, loosened the gas line union with my pipe wrench making sure that the shutoff was working and finished unthreading the pipe.

Once loose, I turned my attention to the water lines. I used side cutters to cut off the old clamps. Once cut, I used the crescent wrench to unscrew the old PEX fittings off of the top of the tank.

Pro tip: keep some old towels around! Water will come out of these lines once loose!

The last thing to do to get the old tank out of there was to loosen the two clamps holding the PVC pipe onto the power vent. This was just a simple flathead to loosen.

Once off, I tipped the tank, drained the rest of the water, closed the drain so water didnt leak when moving it.

I moved the old tank out of the way and cleaned up the floor.

Step 6: Remove Gas Fittings

The old tank still had the Tee and the rest of the gas line attached. It was too big to unscrew as a whole so I had to use my pipe wrench to remove the individual pieces in order to unscrew the tee and nipple from the old tank.

Step 7: Install the New Tank

I reversed the steps and reassembled the fittings on the new tank, but not without cleaning and reapplying pipe dope to the pipes first. The pipes should be tight to prevent leaking. Use your pipe wrench to get things tight.

Before I moved the new tank into place I removed the old PEX fittings off of the line, slipped new 3/4″ PEX clamps onto the lines, and pressed in the new fittings. I did NOT tighten the clamps at this point.

I shimmied the new hot water tank into place, lining it up with the gas line, water lines, and PVC vent.

Once in place, I installed teflon tape onto the hot water tank lines. Pro-tip: wrap them clockwise to make sure it stays on when you thread on the fitting.

Making sure my pipe dope was safe for potable drinking water, I then put some on the teflon tape and threaded the fittings onto the tank using my crescent wrench to snug things up.

When snug, slide the PEX clamps down until its 1/8-1/4″ from the end and use the crimper to crimp the clamps.

At this point, the water side of things are complete.

Moving on to the gas line, I cleaned up and applied more pipe dope onto the union and tightened that up using my pipe & crescent wrenches.

I slipped the PVC onto the new boot on the power vent and tightened down the clamps — do not crank these down as it is just plastic.

I took the pressure relief valve drain tube off of the old tank and installed it onto the new one.

Step 8: Leak Testing

Next was the real test. Did I have any leaks?

I grabbed some soapy dish soap to check for gas leaks. Turn on the gas valve and use the soapy water to check for bubbles. None!

Had I had some, I would have tightened down the pipes more and if needed, disassembled and added more pipe dope.

Gas, check!

Water? Slowly turn on the water valve and let the water come into the new tank. No leaks!

Plug in the power vent, but do not turn on the main power yet.

I like to go to a few faucets and open them until you get a steady flow of water. Be careful, air will spit out with water!

Ive had the tank not start due to air being in the tank so ive always made this good practice.

Once the lines are purged I went back to the tank and did one more walkthrough confirming gas and water valves are in the on position, unit plugged in, and PVC vent attached and clamped down.

Set your water temp on the control unit and flip the switch to on. The unit should start flashing and turn on within a few seconds.

That’s it for the install.

Now to strap the old hot water heater to the dolly and bring it out to the curb. Someone will typically grab it for scrap metal, but if not your trash company may take it if you call and set up a special pickup.