Water heater sizing
Compare water heaters against your household demand.
Explore sample tank and tankless sizing scenarios and general equipment concerns. The results are for planning, not diagnosis or installation approval. A qualified professional must assess your equipment and household requirements.
Tool 1 of 2
Size a water heater
A tank is sized by the hot water it can hand over in the busiest hour of the day. A tankless is sized by how much it can heat at once. Tell it who showers, how many bathrooms, and what else runs in that hour, and watch the tank fill to the size it implies.
People in the house
everyone who showers here
Bathrooms with a shower or tub
caps how many run at once
The busiest hour
tick what happens in the same hour
Fuel
what the house has at the heater
Tank or tankless
two different ways to size
How the math works
A tank is sized by its first-hour rating: the hot water it can hand over in its busiest hour, tank plus recovery. We add up that hour fixture by fixture: 14 gallons of hot per shower at a 2.0 gpm head, 2 per person for sinks, 40 for a soaking tub, 20 for a warm wash and a dishwasher cycle.
A tankless is sized by flow: how many gallons per minute it can heat at once. We assume a 70°F rise, which is roughly 50°F groundwater to 120°F at the tap. Colder water in winter means a bigger rise and less flow from the same unit.
Yearly cost assumes 17 gallons of hot water per person per day, gas at $1.20 to $1.90 a therm, electricity at 14 to 22 cents a kWh, and the efficiency printed on a mid-market unit’s label. Your bill and your water are the real numbers.
Your busiest hour
- 013 showers at 14 gal of hot42 gal
- 02Sinks and shaving, 3 people at 2 gal6 gal
We would quote
40 gal gas tank
A 40 gallon gas tank is typically rated around 70 gallons in its first hour, which covers a 48 gallon hour. The rating on the yellow label of the actual unit is what we size to.
What it costs to run, per year
- Gas tank$190 to $340
- Gas tankless$140 to $250
- Electric tank$480 to $780
- Heat pump tank$120 to $230
- Electric tankless$460 to $730
Installed, with the permit
$1,800to$3,400
Unit, flex connectors, new shutoff, drain pan, expansion tank if the house needs one, and the permit.
An estimate for a conversation. We confirm the size on site from your fixtures, your gas line or your panel, and the label on the unit. The written estimate is what counts.
Tool 2 of 2
What is that sound or smell?
Review the concern closest to your experience. Symptoms alone do not establish a diagnosis; contact an appropriate local professional for assessment and urgent assistance.
Banging pipes
Water hammer. A valve closes fast and the moving water slams to a stop in the pipe. It is loud at the washer, the dishwasher, and single-handle faucets. Pipes that are not strapped make it worse.
Right now
Nothing urgent. If a joint starts weeping after a bang, shut the fixture stop and call. The fix is a hammer arrestor at the offending fixture and strapping the loose run.
When it suits you. The phone number is a demo line.
Near the end
Six signs a heater is telling you something.
- Rust in the hot water onlyThe tank is corroding from the inside. The anode is gone and the steel is next.
- Damp at the base, a ring in the panA weep at the bottom of a tank does not get better. Start choosing the day instead of having it chosen.
- Rumbling or popping while it heatsSediment on the bottom. A flush helps a younger tank; an older one is telling you something.
- The last shower is cold every morningUndersized for the household, or an element or a dip tube has failed. The sizing tool says which is more likely.
- Past ten years on a tankMost tanks last eight to twelve. Past ten, a leak is a matter of when, and a planned swap costs less than a Sunday one.
- The relief valve dripsOften the house needs an expansion tank, not a heater. Sometimes the valve itself. Either is a short visit.
Discuss your plumbing project
Share the scope, your priorities, and the timing you have in mind. This inquiry form is part of the 3Fold Labs website demonstration.