Rheem Professional Classic Gas Water Heater Comparison

Rheem Professional Classic and Professional Classic Plus gas tank water heaters come in three venting families, and the vent type usually narrows the choice before tank size does. Atmospheric models send exhaust up a vertical B-vent or chimney. Direct vent models are sealed units that draw combustion air from outdoors and exhaust through a side wall. Power vent models use an electric blower to push exhaust through plastic pipe. This page compares the 40, 50 and 75 gallon models we carry, including the 38 and 48 gallon tanks sold in the same size classes, with gas input, first-hour rating, tank height and vent type for each. Model numbers with an S after the gallon figure are short, wider tanks for low-clearance spaces.

Atmospheric vent

No electrical connection. The heater needs a vertical vent and enough combustion air in the room.

Atmospheric vent with powered damper

These vent into standard Category I B-vent like an atmospheric model, but add an electrically operated flue damper and need a 120 V outlet nearby.

Direct vent

Sealed combustion through a coaxial vent that passes through an outside wall. Rheem states these models use outside air for combustion and require no electrical power. Vent kits are ordered separately.

Power vent

A blower on top of the heater pushes exhaust through plastic pipe, horizontally or vertically. Combustion air comes from the room. Requires a 120 V outlet.

Power direct vent

Two-pipe sealed combustion with a blower: one pipe brings in outdoor air and one carries exhaust out. Requires a 120 V outlet.

Tank height is measured to the top of the tank. The draft hood, blower or vent connection adds to the installed height; the specification sheet for each model gives the overall figure.

How to choose

• Start with the vent you have. Replacing an atmospheric heater that connects to a vertical B-vent or lined chimney: stay with atmospheric or powered damper. No vertical vent but an outside wall close by: direct vent, which needs no power. A longer run to the outside, or a vent that must go sideways through a rim joist: power vent or power direct vent.
• Check where combustion air comes from. Atmospheric and power vent models burn room air. Direct vent and power direct vent models are sealed and take air from outdoors, which suits tight utility rooms and closets.
• Check for an outlet. Powered damper, power vent and power direct vent models need 120 V at the heater. Atmospheric and direct vent models do not.
• Size by first-hour rating. Rheem’s guidance is to estimate the hot water used in your household’s busiest hour and choose a first-hour rating that meets it. Two 50 gallon tanks can differ: here they range from 76 to 111 gallons in the first hour depending on gas input.
• Use input to compare recovery. A higher BTU/h input reheats the tank faster. The 75 gallon models have a 76,000 BTU/h input and a 4" vent on the atmospheric versions, so confirm the gas line and vent size before moving up from a 50 gallon.
• Measure height and diameter. Short models such as the PROG50S-40N-RH61 are about 51" tall but nearly 24" in diameter; tall 50 gallon models are about 59" tall and 21-1/2" in diameter.

Common questions

What is the difference between power vent and direct vent?

A direct vent water heater is sealed, takes combustion air from outdoors through a coaxial vent and needs no electricity. A power vent water heater uses room air and an electric blower to push exhaust through plastic pipe, which allows longer and more flexible vent runs.

Can I replace an atmospheric water heater with a power vent model?

Yes, but it is not a like-for-like swap. A power vent model needs a new plastic vent run to the outdoors, a 120 V outlet and a way to deal with the old B-vent opening. If other appliances share the old vent or chimney, it has to be re-evaluated for what remains connected. Vent sizes and length limits are in the installation manual for each model. Gas piping, venting and combustion air work must follow the installation manual and local code and, in most jurisdictions, must be done by a licensed installer.

What does the S mean in a Rheem model number such as PROG40S-38N?

It marks a short tank. A short 40 gallon model is about 50" tall, against 58" to 63" for the tall 40 gallon models, and is wider to keep the same capacity.

What is the difference between Professional Classic and Professional Classic Plus?

They are two tiers of the same Rheem gas tank range. Model numbers beginning PROG are Professional Classic; those beginning PRO+G are Professional Classic Plus. Compare the specifications and warranty terms on each product page.

Related collections

• Residential gas tank water heaters
• Rheem 40 gallon water heaters
• Rheem 50 gallon water heaters
• Water heater vent kits
• Manufactured housing water heaters
• All Rheem products