In short
- A barndominium water heater size calculator starts from your busiest hour of hot-water use, not the number of bedrooms: showers, shaves, dishes and laundry in that one hour.
- Each shower counts about 10 gallons, a dishwasher load 6, a laundry load 7, a shave 2 and hand dishes or food prep 4 (U.S. Department of Energy worksheet).
- For a tank, look for a first hour rating within about 2 gallons of that total. For tankless, add the flow of fixtures running together and the temperature rise.
- Two showers, a shave, a dishwasher load and a laundry load come to about 35 gallons: a first hour rating of roughly 33 to 37.
On this page
This barndominium water heater size calculator is for Tyler and Smith County owners planning a barndominium who want to know what size to ask the builder or plumber for before the plumbing is ordered. Enter what runs in your busiest hour and it gives the first hour rating to look for on a tank heater, plus the flow and temperature rise a tankless unit would need. It sits beside our electrical service size calculator, which counts the water heater as an electric load.
En español: calculadora de tamaño de calentador de agua
Tank water heater: busy-hour use
| Use | Gal x times | Gallons |
|---|
Tankless: flow and temperature rise
| Typical unit | gal/min at 70 °F rise | At your rise | Covers it? |
|---|
Example: 2 showers, 1 shave, 1 dishwasher load and 1 laundry load in the busiest hour; for tankless, 2 showers at 2.0 gal/min and 1 tap at once, 50 °F in, 120 °F out.
How the sizes are worked out
- Count the busiest hour.
Multiply each use by the gallons the DOE worksheet gives it: shower 10, shave 2, hand dishes or food prep 4, dishwasher load 6, laundry load 7. Example: 2 x 10 + 1 x 2 + 1 x 6 + 1 x 7 = 35 gallons.
- Match the first hour rating.
The DOE says to pick a model whose first hour rating is within 1 or 2 gallons of that total. This tool shows the total minus 2 to the total plus 2: 33 to 37 gallons.
- For tankless, add the flows.
Flow = showers x showerhead flow + taps x 0.75. Example: 2 x 2.0 + 1 x 0.75 = 4.75 gallons per minute.
- Work out the rise.
Rise = hot temperature minus cold temperature. Example: 120 - 50 = 70 degrees F.
- Compare with a typical unit.
The DOE gives about 5 gal/min for gas-fired and 2 gal/min for electric units at a 70 degree rise. We scale those by 70 / your rise as a rough guide (our planning assumption): a bigger rise means less flow.
Busy hours and the first hour rating to look for
| Busiest hour | Peak use | First hour rating |
|---|---|---|
| 2 showers, 2 shaves | 24 gal | 22 to 26 gal |
| 3 showers, 1 dishwasher load, 1 laundry load | 43 gal | 41 to 45 gal |
| 4 showers, 1 shave, 1 dishwasher load, 1 laundry load | 55 gal | 53 to 57 gal |
Computed with the DOE worksheet figures and no water-saving fixtures. A different morning gives a different answer: use the calculator with your own count.
Gallons per use in the DOE worksheet
| Use | Gallons each |
|---|---|
| Shower | 10 gal |
| Shave | 2 gal |
| Hand dishes or food prep | 4 gal |
| Dishwasher load | 6 gal |
| Laundry load | 7 gal |
These assume standard use with no water conservation measures, per the DOE worksheet. Low-flow fixtures use less, so the tool errs on the high side.
Where water heater sizing goes wrong
- Sizing by tank gallons. A 50-gallon tank does not deliver 50 gallons in the first hour. The first hour rating on the label is the number to compare.
- Sizing for an average day. The worksheet is built on the single busiest hour, because that is when the heater runs short.
- Forgetting the shop or guest bath. If a shop sink, a second bath or a bunk room shares the heater, add their busy-hour uses too, or ask about a second heater.
- Tankless flow vs cold water. A tankless unit loses flow as the incoming water gets colder. Check its rating at your rise, not only the headline number.
- Ignoring the electric side. An electric tank or tankless unit is a large electrical load. The electrical service size calculator counts it.
What to ask your builder
- What fuel and type is the water heater? Tank or tankless, electric, propane or natural gas. See the electric service guide for what is available at your lot.
- What is its first hour rating, or its flow at my temperature rise? Ask for the number on the EnergyGuide label or the maker's rating at the rise for your area.
- Where is it placed? Ask how far it is from the bathrooms and kitchen, and who pays if the plan changes.
- Is it in the base price? Check that the heater, its venting or electrical supply and any expansion tank are listed, not left as an allowance. See how to choose a barndominium builder.
Next step: get a written quote
This tool sizes a water heater, not the building or the price. We are a referral service, not a contractor; we connect visitors with independent local providers. Use the form below to ask independent barndominium builders near Tyler for a written quote that names the water heater type, fuel and first hour rating, and read how to choose a barndominium builder first.
Sources
- Sizing a New Water Heater, U.S. Department of Energy, Energy Saver: first hour rating, peak hour worksheet (10, 2, 4, 6 and 7 gallons), 50 °F and 120 °F assumptions, and typical tankless flow at a 70 °F rise.
- Showerheads, U.S. EPA WaterSense: the 2.0 gallons per minute limit for labeled showerheads.
Frequently asked questions
What size water heater does a barndominium need?
Size a tank water heater by its first hour rating (the gallons of hot water it can deliver in the first hour), not by tank volume. The U.S. Department of Energy says to estimate the most hot water your household uses in its busiest hour and pick a model whose first hour rating is within 1 to 2 gallons of that figure. This calculator does that arithmetic.
Where do I find a water heater's first hour rating?
On the yellow EnergyGuide label, top left, listed as "Capacity (first hour rating)". The label is required on new conventional storage water heaters but not on heat pump water heaters, so for those ask for the manufacturer's literature.
How do I size a tankless water heater?
Add up the flow of the hot-water fixtures that may run at the same time, in gallons per minute, then work out the temperature rise (the hot temperature you want minus the incoming cold temperature). The DOE gives a typical 70 degree rise as possible at about 5 gallons per minute for gas-fired units and 2 gallons per minute for electric ones. Check the maker's rating for the exact model.
What incoming water temperature should I use in East Texas?
The DOE says to assume 50 degrees F unless you know otherwise. Incoming water can be colder in winter, which raises the rise a tankless unit must deliver, so the tool lets you try 40 to 70 degrees. Ask the installer what the incoming temperature is at your property.
Does this count how many people live in the house?
No. The DOE worksheet counts what runs in the busiest hour, not people, and it does not estimate daily use. Think about the busiest hour of a normal day, such as the morning when several people shower, and enter those uses.
Does the calculator give a price?
No. It gives sizes only, with no prices. Ask for written quotes that name the heater's first hour rating (or tankless flow and rise) and the fuel.