Water Heater Install Calculator — Size & Cost
Find the right water heater size and a ballpark install cost. Enter your household, pick tank, tankless, or hybrid, and get a recommended capacity (gallons or GPM) plus an installed cost estimate — with a tank-vs-tankless-vs-hybrid comparison and a downloadable PDF.
| Option | Recommended | Est. installed |
|---|---|---|
| Run the calculator to compare options | ||
How to use the water heater install calculator
Four quick steps turn your household into a recommended water heater size — gallons or GPM — and a ballpark installed cost, with a tank-vs-tankless-vs-hybrid comparison and a downloadable estimate.
Pick system & fuel
Choose tank, tankless, or hybrid, and your fuel. Fuel sets how fast the heater recovers — and the default price.
Enter the demand
Add household size, bathrooms, usage level, and incoming-water climate — the drivers of peak hot-water demand.
Set the cost
The installed unit price auto-fills by type and fuel; add extras, a permit, and a contingency.
Read results & save a PDF
Get the recommended size, peak demand, and project total, plus a three-way comparison — then download an estimate.
How the size & cost are estimated
Sizing starts from peak-hour demand, then converts to a tank size (by fuel recovery) or a tankless flow rate. Cost follows from the unit and extras. Here is the exact math.
Worked example — 4 people, 2 bathrooms, average usage, gas storage tank
Peak demand: (4×12 + 2×5) × 1.0 = 58 gal
Tank size (gas ÷ 1.8): 58 / 1.8 = 32 → next standard 40 gal
Cost: $1,800 unit + $350 extras + $150 permit = $2,300
With 10% contingency: $2,300 × 1.10 = $2,530
≈ 40-gallon gas tank · project total about $2,530. (Electric would size to ~50 gal.)
Water heater sizing & cost charts
Handy lookups for tank size by household, tankless flow by bathrooms, installed cost by type and fuel, and the sizing rules of thumb. These are ballparks — a plumber confirms the real size.
| Household | Peak demand | Gas tank | Electric tank |
|---|---|---|---|
| 1 person | 22 gal | 30 gal | 30 gal |
| 2 people | 34 gal | 30 gal | 30 gal |
| 3 people | 46 gal | 30 gal | 40 gal |
| 4 people | 58 gal | 40 gal | 50 gal |
| 5 people | 70 gal | 40 gal | 66 gal |
| 6 people | 82 gal | 50 gal | 66 gal |
Gas recovers faster, so a gas tank runs a size smaller than electric for the same demand. Heavy usage bumps these up.
| Bathrooms | Base flow | Rough fixtures at once |
|---|---|---|
| 1 bath | 3.5 GPM | A shower plus a sink |
| 2 baths | 5 GPM | Shower + sink, or two showers |
| 3 baths | 7 GPM | Two showers + a fixture |
| 4+ baths | 9 GPM | Multiple simultaneous uses |
Tankless is sized by flow, not gallons. Colder incoming water lowers a unit’s effective GPM, so cold climates need more capacity.
| Type | Gas | Electric | Propane |
|---|---|---|---|
| Tank (storage) | ~$1,800 | ~$1,600 | ~$1,900 |
| Tankless | ~$3,500 | ~$2,200 | ~$3,600 |
| Hybrid (heat pump) | — | ~$2,800 | — |
Installed (unit + standard labor). Hybrids are electric-only heat-pump tanks. Extras, permit, and a fuel/type change add cost.
| Factor | Rule |
|---|---|
| Per person | +12 gal of peak demand |
| Per bathroom | +5 gal of peak demand |
| Gas tank | demand ÷ ~1.8 (fast recovery) |
| Electric tank | demand ÷ ~1.3 (slow recovery) |
| Hybrid tank | demand ÷ ~1.4 |
| Tankless | sized by GPM, not gallons |
Standard tank sizes are 30, 40, 50, 66, and 80 gallons — the calculator rounds up to the next one.
Everything the calculator works out
A few household details give you both the right size and a budget — plus a side-by-side of all three system types.
Key figures behind the sizing
Built for a smart replacement
From a homeowner’s first look to a plumber’s quick check, the same calculator turns a household into a size and a budget.
Replacing an aging heater and wants the right size and a realistic cost before calling plumbers.
- Enter household & bathrooms
- See recommended gallons or GPM
- Take the number into your quotes
Weighing the three system types on size and up-front cost before deciding which to buy.
- Read the three-way comparison
- Flip fuel to see the effect
- Weigh up-front vs efficiency
Wants a fast ballpark size and price to share, then confirms against the actual fixtures.
- Set price by type & fuel
- Add extras & permit
- Hand the PDF to the client
7 tips for the right water heater
Sizing is about the busy hour, not the whole day. These points keep the estimate honest and point you to the details that matter.
Water heater install calculator FAQ
The sizing, type, and cost questions people ask most before replacing a water heater.
Size to your peak-hour demand, not just the number of people. A rough rule is about 12 gallons per person plus 5 per bathroom for the busiest hour, adjusted for usage.
For a tank, divide that by a recovery factor — roughly 1.8 gas or 1.3 electric — and round up. A family of four with two baths needs about a 40-gallon gas or 50-gallon electric tank. Tankless is sized by flow (GPM).
A licensed plumber should confirm the size against your actual fixtures and incoming water temperature.
For a storage tank, work from first-hour demand:
1. Peak demand = (people × 12) + (bathrooms × 5), times a usage factor
2. Tank gallons = demand ÷ recovery factor (~1.8 gas, ~1.3 electric)
3. Round up to a standard size — 30, 40, 50, 66, or 80 gal
For tankless, don’t use gallons — size by gallons per minute (GPM) of simultaneous flow, adjusted for the temperature rise your climate needs. Colder incoming water needs more capacity.
A typical four-person household with two bathrooms has a peak-hour demand around 58 gallons.
That points to roughly a 40-gallon gas or 50-gallon electric tank, a 50-gallon hybrid, or a tankless around 5–7 GPM. Heavy usage — long showers, a soaking tub, laundry and showers at once — pushes those up a size.
Match the size to how your household actually uses hot water, and confirm with a plumber.
They solve it differently. A storage tank keeps a fixed number of gallons hot — cheaper to install, but can run out during heavy back-to-back use and loses standby heat. A tankless heats on demand for endless hot water and lower standby loss, but costs more up front and is limited by its flow rate.
Tanks suit tighter budgets and steady demand; tankless suits homes wanting endless hot water, space savings, or lower operating cost. A hybrid heat-pump tank is a very efficient third option.
The best pick depends on budget, fuel, space, and usage — get a plumber’s recommendation.
A hybrid, or heat-pump, water heater is an electric storage tank that pulls heat from the surrounding air to warm the water instead of using resistance elements alone. That makes it two to three times more efficient than a standard electric tank.
The trade-offs: it needs a fair amount of surrounding air and space (garage, basement, or utility room with clearance), costs more up front, and cools and dehumidifies the space it sits in. It’s electric-only.
For many homes the energy savings pay back the higher price over time.
Yes — through recovery rate, how fast the heater reheats water during use. Gas burners reheat faster than electric elements, so a gas tank delivers more hot water per stored gallon.
Because of that, a gas tank can be smaller than an electric one for the same demand. The calculator divides demand by ~1.8 for gas versus ~1.3 for electric, which is why a 40-gallon gas need might be a 50-gallon electric.
Fuel also affects operating cost and venting requirements.
Installed cost depends on type and fuel. Rough figures: a standard tank about $1,600–$1,900, a tankless about $2,200 electric to $3,500 gas, and a hybrid heat-pump around $2,800.
On top of the unit, budget for extras — expansion tank, venting, a gas-line or electrical upgrade, drain pan, or code work — plus a permit and a contingency.
A like-for-like tank swap is cheapest; changing type or fuel adds cost. Prices vary by region — get written quotes from licensed plumbers.
First-hour rating (FHR) is how many gallons of hot water a storage tank can deliver in a busy hour starting full. It combines stored volume with reheat speed, so it reflects real capacity better than tank size alone.
That’s why a smaller gas tank can match a larger electric one — the gas unit’s faster recovery gives it a higher FHR.
When shopping tanks, compare FHR against your peak-hour demand rather than just gallons. Tankless units use a GPM flow rating instead.
Sizing & Budget Notice: This calculator recommends a water heater size from typical first-hour-demand and flow rules of thumb, and estimates installed cost from national-average prices by type and fuel. Actual sizing depends on your specific fixture flow rates, simultaneous use, and incoming water temperature, and it is not a substitute for a professional assessment. Prices vary by brand and region, and the estimate does not cover gas-line, venting, electrical, or code work, which are safety-critical and must be handled by a licensed plumber. Confirm the correct size and get a written quote before purchasing or installing. For planning purposes only.