Draw pattern
A draw pattern is the standardized daily hot-water usage profile (Very Small, Low, Medium, or High) a water heater is tested under for its UEF rating. It indicates the household size the unit is designed to serve.
The DOE test procedure assigns each model one of four patterns based on its capacity — from Very Small (about 10 gallons per day, point-of-use units) to High (around 84 gallons per day, large-family units). The UEF number is only comparable between models tested on the same pattern.
For buyers, the pattern is a quick size class: a High-usage-rated unit is engineered for the demand of a large household, while a Low-usage unit will run efficiently in a small one.
| Very Small | ~10 gallons per test day — assigned to units under 18 gal FHR or 1.7 GPM |
|---|---|
| Low | ~38 gallons per day — FHR 18 to under 51 gallons, or 1.7 to under 2.8 GPM |
| Medium | ~55 gallons per day — FHR 51 to under 75 gallons, or 2.8 to under 4 GPM |
| High | ~84 gallons per day — FHR 75 gallons and up, or 4 GPM and up |
| Test conditions | 58 °F inlet water, 125 °F thermostat setting, 67.5 °F ambient air |
| Certified market split | Of models on this site: 820 High, 267 Medium, 13 Low |
How a model gets its pattern
The manufacturer does not choose. DOE assigns the draw pattern from the unit’s own measured capacity: first-hour rating for storage heaters, maximum flow rate for tankless. Under 18 gallons FHR (or 1.7 GPM) is Very Small; 18 to under 51 is Low; 51 to under 75 is Medium; 75 and above is High. The certified data on this site matches those cut-offs exactly — the Low-pattern models rate 45 to 50 gallons FHR, Medium runs 51 to 73, and every High-pattern storage model is 75 or more.
The tankless side follows the same logic on flow: a 3.8 GPM unit in the certified listings is tested on Medium and everything from 4.3 GPM up is tested on High. Because virtually all residential gas tankless models clear 4 GPM under the test’s own conditions, the tankless market is almost entirely High-pattern.
Each pattern is a scripted 24-hour schedule of draws, not just a daily total. Very Small is a handful of small draws totalling about 10 gallons, appropriate to a point-of-use heater under a sink. High is a busy household’s day — roughly 84 gallons across morning and evening clusters, including a large draw the unit has to recover from.
Why UEF only compares within a pattern
Standby loss is roughly constant: a tank sheds heat through its jacket at about the same rate whether you use 38 gallons a day or 84. UEF divides useful output by total input, so the more hot water the test draws, the smaller a share those fixed losses represent — and the higher the resulting number. Take one physical heater and test it on Low instead of High and its UEF falls, with nothing about the appliance having changed.
That is why cross-pattern comparison is meaningless in a specific direction: a Medium-pattern unit at UEF 0.88 may be a better-built appliance than a High-pattern unit at UEF 0.90. Every listing on this site shows the pattern alongside the rating for exactly this reason, and comparison pages pair the two figures rather than ranking UEF alone.
The annual energy figures inherit the same problem. Certified gas storage models tested on High cluster at 182–197 therms a year because the test day is 84 gallons, not because your household uses that much. If your real consumption is closer to 45 gallons a day, every certified annual-cost figure — including the ones on this site — is roughly half again too high in absolute terms, though the ranking between models still holds.
Using the pattern when you shop
Treat it as a coarse size class that has already been computed for you. A High-pattern unit was tested against the demand of a four-or-more-person household; a Medium-pattern unit against something closer to two or three people. If your peak-hour arithmetic points at 60 gallons and a model is rated on the Low pattern, that model is too small regardless of how good its UEF looks.
The mismatch runs the other way too, and it is the case most people miss. Put a High-pattern 80-gallon heater in a one-person apartment and its real-world efficiency will be worse than its label, because the same standby losses are now spread across a quarter of the hot water the test assumed. Oversizing a tank is not free; it is a permanent standby-loss tax.
Two practical checks. Compare candidates within a pattern first, and only then across patterns with the size difference in mind. And when a manufacturer quotes a UEF without naming the pattern, look it up in the certification record before believing it — the number on its own is not a specification.
Frequently asked questions
What does draw pattern mean on a water heater?
It is the standardized daily hot-water usage schedule — Very Small, Low, Medium, or High — that DOE runs a water heater through to measure its Uniform Energy Factor. The pattern is assigned from the unit’s own first-hour rating or maximum flow rate, and it determines both the UEF and the annual energy-use figure printed on the EnergyGuide label.
Which draw pattern do I need?
You do not pick one — it is assigned to the model, not chosen by you. Use it as a size signal: High corresponds to a unit sized for a busy household of four or more (an 84-gallon test day), Medium to two or three people (55 gallons), Low to one or two (38 gallons). Then size properly using first-hour rating or GPM.
Does a High draw pattern mean a water heater is more efficient?
No. It means the unit was tested against more daily hot water, which mathematically flatters its UEF because fixed standby losses are spread over a larger output. A High-pattern model at UEF 0.90 and a Medium-pattern model at UEF 0.88 may well be equally efficient appliances.
How much hot water does the DOE test draw each day?
About 10 gallons on the Very Small pattern, 38 on Low, 55 on Medium, and 84 on High, delivered as a scripted series of draws over 24 hours with 58 °F inlet water and a 125 °F thermostat setting. Those daily volumes are also the basis for the annual energy consumption listed on every certified model.