Can you swap a tank water heater for a tankless?
Yes, in most homes, but not as a one-for-one swap. A tank heater needs a small gas burner or a single 240 volt circuit. A whole-house tankless gas unit burns far more fuel at once, often in the range of 150,000 to 200,000 BTU, compared with roughly 30,000 to 50,000 for a typical tank.
That jump is why the gas line, the vent and the water supply all get a second look. The question is not whether tankless works, but what your house needs to run one safely.
Tank versus tankless: a decision table
Use this to see which kind of home fits which heater. There is no winner for every house.
| Question | Tank heater fits better | Tankless fits better |
|---|---|---|
| How much hot water at once? | Small household, light use | Large household, back to back showers |
| How much space do you have? | Closet or corner with floor room | Tight wall space, you want the floor back |
| What is your current gas line? | Half inch line, no room to upgrade | Three quarter inch line or a plan to upsize |
| How hard is the water? | Untreated hard water you will not soften | Soft or softened water, or willing to flush yearly |
| How long do you plan to stay? | A few years | Ten years or more |
| How tight is the upfront budget? | Lower installed cost | Higher installed cost, lower running cost |
If you want a straight tank swap instead, read about water heater replacement to see how the two jobs differ.
Gas line, vent and power: the three checks
These decide the scope of the job before any unit is ordered.
Gas line size
A big gas tankless often needs a 3/4 inch line close to the unit, and the meter must be able to supply the added load. A plumber checks this first.
Vent material and route
Tank heaters use a draft hood. Many tankless units are sealed and use special vent pipe through a wall or roof. The vent route can be the hardest part of the job.
Condensate drain
High efficiency units make acidic water that needs a drain and sometimes a neutralizer. Plan where it will go.
Electric power
An electric tankless can need several 40 to 60 amp circuits. Your panel may not have room, which can make electric a poor fit.
Old tank leaking right now?
Our line is answered 24/7. Shut off the cold supply at the tank and call us.
If you smell gas during a swap
Natural gas is odorized with a sulfur or rotten egg smell. Any gas work, including capping the old line, is a job for a licensed plumber and not a weekend project.
If you smell gas at any point:
- Stop work and leave the building immediately, leaving doors open if safe
- From a safe place, call Enbridge Gas at 1-800-767-1689 or 911
- Do not use phones, light switches or anything electric inside
- Do not search for or try to fix the leak yourself
Permits and inspections for a water heater swap in Midvale
Midvale's building page says water heater replacement requires a building permit and building inspections. That includes swapping a tank for a tankless. Permits are submitted online, and inspection requests are online at least 24 hours ahead, Monday to Thursday 8 a.m. to 3 p.m. Only the contractor on record can schedule the inspection.
The practical effect is timing. Inspections need 24 hours of notice and run only Monday to Thursday, so a tankless install with a new vent and gas run should be planned around that window. Midvale Building and Safety is at City Hall, 7505 S Holden Street, and the office is closed Friday to Sunday. Ask them about the rules for gas and vent work on your house.
How a tankless replacement usually goes
Each house differs, but this is the common order of work.
- 1
Walk the house
Check gas size, vent route, electrical panel and water pressure.
- 2
Size the unit
Add the flow of fixtures you run at once to choose a gallons per minute rating.
- 3
Permit and shutoff
The contractor files the permit and plans the shutoff window.
- 4
Remove and install
Drain the old tank, mount the new unit, run gas, vent and water lines.
- 5
Inspect and test
A city inspection follows, then startup and flow tests.
DIY or licensed plumber for a tankless swap
Gas and venting are the reasons this is rarely a homeowner job.
What a homeowner can reasonably do
- Compare models by flow rate and fuel type
- Measure the wall space and note the gas line size
- Clear the area and shut off water at the main
- Count how many fixtures run hot water at once
What needs a licensed plumber
- Running or upsizing the gas line
- Cutting and sealing the vent
- Pulling the permit and scheduling inspections
- Connecting the condensate drain
- Testing combustion and leaks
We are plumbers, not electricians. If an electric unit needs a panel upgrade, a licensed electrician handles that part, and we can coordinate the plumbing.
Mineral scale and long-term care
Tankless heaters have narrow heat exchanger passages that scale up with hard water. A yearly flush with a descaling solution is the usual advice, and a softener upstream helps. If you are not sure about your water, test your tap or ask your utility, since the supply differs across Midvale.
A scaled unit shows up as lukewarm water, error codes or noise. A flush is a routine service, and our tankless water heater page explains what we do.
When to call a pro
Call a plumber before you buy a unit. A visit to check the gas line and vent can show whether tankless suits your house or whether a new tank is the smarter choice. If your tank is already leaking, shut off the cold supply and call, because a flood is faster than a swap.
We serve Midvale and nearby towns, including Sandy, and you can see more coverage on the areas page.
Where this guidance comes from
The permit rule comes from Midvale City's building page, and the install follows the International Plumbing Code (IPC) and the maker's guidelines.
Tankless replacement questions from Midvale homeowners
Sometimes, but many tankless units need a larger line than a tank heater. A plumber measures the run and checks the meter capacity before the unit is ordered.
Yes. Midvale's building page says water heater replacement requires a building permit and building inspections, and inspections are requested online at least 24 hours ahead.
Usually not. Many tankless units use a sealed, special vent pipe, and an old draft hood vent may be the wrong material or size.
A simple swap can be done in a day. A job that needs a new vent, gas run or permit wait takes longer. We will tell you what your house needs before we start.
No. It heats as water flows, so it never runs out of stored water, but it has a maximum flow rate. Too many fixtures at once can drop the temperature.
None. A water heater is part of your home plumbing, so a leak is yours to fix. For water emergencies on the city side, Midvale Public Works answers 24/7 at 801-567-7235.