Tall and short tank water heaters of the same nominal size hold about the same water. The short one is lower, and often wider. State's 40-gallon gas models stand 58.25 and 47.75 inches tall; A. O. Smith's 50-gallon electrics, 59 and 49.25. Measure height, width and the connection points before choosing.
How much shorter is a short water heater?
About ten inches in the pairs below, with no loss of rated storage. These figures are from the makers' own product pages for matched short and tall models.
| Model | Height | Diameter | Nominal / rated storage |
|---|---|---|---|
| State ProLine 40-gal gas, short (GS6-40-BRBS) | 47.75 in. | 20 in. | 40 / 38 gal |
| State ProLine 40-gal gas, tall (GS6-40-OCT) | 58.25 in. | 20 in. | 40 / 38 gal |
| A. O. Smith ProLine 50-gal electric, short (ENS-50) | 49.25 in. | 23 in. | 50 / 46 gal |
| A. O. Smith ProLine 50-gal electric, tall (ENT-50) | 59 in. | 20.5 in. | 50 / 46 gal |
| State ProLine 50-gal electric, lowboy (ESX-50-DOLS) | 36 in. | 26.5 in. | 51 / 48 gal |
Two things stand out. In the 40-gallon gas pair, the short model is just as narrow, so the saving is all in height. In the 50-gallon electric pair, the short model is 2.5 inches wider. The lowboy, a separate low, wide style, is the shortest here at 36 inches and the widest at 26.5.
These are individual models. Another maker's short 40 may differ by an inch or two, so compare the spec sheet for the exact model.
Does a short heater deliver less hot water?
Not because of its height. Tank size sets how much hot water is on hand, and ENERGY STAR notes that tank size generally translates to how much space the heater takes up. What a tank delivers over a busy hour is the first hour rating (FHR). ENERGY STAR defines it as "An estimate of the maximum volume of hot water in gallons that a storage water heater can supply within an hour that begins with the water heater fully heated."
That rating depends on the model's heating power as well as its size. ENERGY STAR gives the example that a 40-gallon tank with a very high-powered heating element might produce 80 gallons in the first hour, while a lower-powered one might need an 80-gallon tank to do the same.
The product pages show how it varies. A. O. Smith lists a first hour rating of 57 gallons for the short 50-gallon electric and 62 for the tall one. State lists 51 for its lowboy. So compare the FHR on the label, not the height class. Our page on what size water heater you need shows how to match it to your household, and water heater recovery time covers what happens after the first hour.
When does a short heater make sense?
It makes sense where height is the limit: a low closet door, a short platform, a ceiling or attic hatch, or a spot where the old unit was a short model. A tall one makes sense when you have headroom and floor space is the tight part, since it can have the narrower footprint.
Height also moves other parts. The State pair lists the height to the temperature and pressure relief valve as 41.25 inches for the short model and 51.75 for the tall one, so the valve sits about ten inches lower on the short model. Both models put the water connections on top. Our page on swapping to a smaller tank explains why a different height or diameter can turn a simple swap into a bigger job.
Building codes also care about space around the unit and, for gas heaters in a garage, how high the burner sits above the floor. Those rules don't depend on the tall or short label, and we cover them in water heater clearance and access code and the garage 18-inch rule.
What should you do before you choose?
- 1Measure the space. Height, width and depth, plus the door or hatch the heater has to pass through.
- 2Read the old label. Note its fuel, nominal gallons and first hour rating.
- 3Match the spec sheet. Compare height, diameter, height to the relief valve and the vent and connection locations on the new model.
- 4Match the first hour rating, not the height class. A short model with the same or higher FHR does the same job.
- 5Check the permit rules. See the Phoenix water heater permit.
HQ Plumbing & Air replaces water heaters for homes, businesses and apartment buildings. We're licensed and insured, and we give free estimates, so we can measure your space and tell you which style fits.