Your water heater dies on a Tuesday and suddenly you’re making a decision you didn’t plan to make: swap in the same tank you had, or spend more upfront on a tankless unit that’s supposed to pay you back later. Both are legitimate choices. Here’s the real math so you’re not guessing under pressure with a plumber standing in your basement.
Bottom line
$600 – $5,600 installed
A like-for-like tank swap: $600-$3,100 (most land $900-$1,800). A tankless upgrade: $1,400-$5,600 (most land $3,000-$4,500).
Two Honest Options, Not a “Right Answer”
This isn’t a case where one option is secretly better and installers are hiding it from you. Both are real, defensible choices:
- Quick tank swap: cheaper upfront, faster (usually done same day), and a fine choice if you’re not planning to stay in the house long or don’t want to spend more right now.
- Tankless upgrade: costs more to install, but lasts almost twice as long (15-20 years vs. 8-12 for a tank) and saves $100-$200 a year in energy. Over 20 years, the numbers usually tilt toward tankless being cheaper overall once you count a tank’s replacement cycle.
Neither of these is a DIY project, for what it’s worth — you’re dealing with gas lines, 240V electrical circuits, or both, plus code-required venting. This is one of the few areas where “just do it yourself to save money” is a genuinely bad idea, not just an inconvenience. Get a licensed plumber either way; the decision that’s actually yours to make is tank vs. tankless, not DIY vs. professional.
Find Your Number
| Household | Tank Swap (installed) | Tankless (installed) |
|---|---|---|
| 1 bath, 1-2 people | $600 – $1,400 | $1,400 – $2,800 |
| 2 bath, 3-4 people | $900 – $1,800 | $2,800 – $4,000 |
| 3+ bath, 5+ people | $1,200 – $3,100 | $3,500 – $5,600 |
Tankless sizing is really about peak flow rate (GPM), not headcount — a house running two showers and a dishwasher at once needs more capacity than the math above assumes. A plumber will size it off your actual fixture count, not a household-size chart. Undersizing is the single most common tankless mistake: it shows up as a lukewarm shower the second someone else turns on a faucet.
Why Tankless Costs More to Install
- Gas units need a two-pipe venting system and often a larger gas supply line (3/4″ minimum) — that alone is $350-$2,000, and can hit $2,000 if there’s no gas line at all yet.
- Electric units often need a 200-amp panel and multiple dedicated 240V circuits. A panel upgrade runs $850-$1,700 on top of the unit and labor.
- Labor alone is $600-$2,500 for 3-10 hours of work, more if venting or electrical work is involved.
A tank swap almost never needs any of this if you’re replacing like-for-like in the same spot with the same fuel type — that’s most of why it’s so much cheaper to install.
The 20-Year Math
This is the part that actually matters for the tank-vs-tankless decision, not just the sticker price:
- Tank, 20 years: roughly $14,800-$20,800 total once you count two replacement cycles (tanks last 8-12 years, occasionally 15 with real maintenance) plus higher ongoing energy bills.
- Gas tankless, 20 years: roughly $12,000-$18,000 total — one unit, lower energy bills, if you descale it periodically in hard-water areas.
So tankless usually wins on total cost of ownership, but the gap isn’t dramatic, and it assumes you stay in the house long enough to see it play out and actually maintain the unit. If you’re selling in three years, the cheaper tank swap is the financially rational choice, not the “lesser” one.
The Third Option Nobody Mentions: Heat Pump Water Heaters
There’s a middle option most quotes won’t bring up unless you ask: a hybrid heat pump water heater. It pulls heat from the surrounding air instead of burning gas or using pure electric resistance, and runs $2,500-$6,500 installed — roughly in between a tank and a gas tankless. It’s the most efficient of the three by a wide margin, but it needs a decent-sized space with airflow (a small closet won’t cut it), produces cool exhaust air and some condensate drainage, and recovers hot water slower than tankless during heavy use. Worth asking about if efficiency matters more to you than upfront cost or recovery speed — just don’t assume the federal tax credit picture is the same as it was a year ago; incentive rules have shifted, so check your state energy office and utility for current rebates rather than relying on older articles.
Practical Tips
- Get quotes for both options, not just one. A plumber who only quotes tankless (usually a bigger job for them) or only quotes tank (less work to sell) isn’t necessarily giving you the full picture. Ask for both prices.
- Ask what “installed” includes. Permits, gas line or panel upgrades, and disposal of the old unit sometimes get itemized separately after the fact. Get it all in one written quote.
- Don’t undersize a tankless unit to save money. A too-small unit that can’t keep up during peak use is a worse outcome than just buying a tank in the first place.
- Check for rebates. Some utilities and states offer $50-$500+ rebates for efficient tankless or heat-pump water heaters — worth five minutes of searching before you buy either option.
- Descale a tankless unit yearly in hard-water areas. Skipping this is the main reason tankless units fail early and don’t hit their 15-20 year lifespan.
Costs above are national averages from current plumbing industry and contractor pricing data as of mid-2026. Actual pricing varies by region, local labor rates, and your home’s existing gas/electrical setup — get two or three written quotes from licensed plumbers covering both a tank and tankless option before deciding.