There is no single "best" gas water heater. The best one for your home is the one that matches your venting, your gas supply, your hot water demand and the space you have. A top-rated model with the wrong vent type can cost more to install than the heater itself. This guide shows you how to compare gas tank water heaters on the specs that matter, in the order a plumber would check them.
1. Start with the vent type
Venting decides which models can go in your home without major changes. It is the first filter, before price or brand. Residential gas tanks use five main vent types:
| Vent type | How it works | Best fit |
|---|---|---|
| Atmospheric | Exhaust rises by natural draft through a draft hood into a B-vent or chimney. | Direct replacement where an existing vertical flue is in good condition. No electricity needed for venting. |
| Powered damper | Atmospheric venting with a damper that closes the flue between burner cycles. | Same flue as atmospheric, with less standby heat loss up the chimney. |
| Power vent | A blower pushes exhaust through plastic pipe, often out a side wall. | No chimney nearby, or the flue is shared or unusable. Needs a 120V outlet. |
| Direct vent | A sealed system that draws combustion air from outside and vents by natural draft through a wall. | Tight spaces and closets, with no electricity needed for venting. Vent terminal location is limited. |
| Power direct vent | A blower plus sealed combustion, with intake and exhaust both piped outside. | Longer vent runs and sealed installations. Needs a 120V outlet. |
If you are replacing an existing heater, the simplest path is almost always the same vent type you have now.
2. Match the fuel: natural gas or propane
Natural gas and propane models are built differently: the gas valve, orifice and burner are specific to the fuel. Buy the version that matches your supply. Some models can be field-converted with a manufacturer kit, but many cannot. Check the rating plate and model number. In Rheem's naming, an "N" usually means natural gas and a "P" means propane (for example, PROG50-36N and PROG50-36P).
3. Size by first-hour rating, not just gallons
The first-hour rating (FHR) is how much hot water the heater can deliver in one busy hour. It is printed on the EnergyGuide label. Two 50-gallon tanks can have different FHRs because their burners are different sizes. Add up your busiest hour (about 10 gallons per shower, plus any dishwasher or laundry), and choose a model whose FHR meets or slightly exceeds it. For help with the numbers, see What Size Water Heater Do I Need?
4. Compare BTU input and recovery
BTU/h input is the size of the burner. A higher input reheats water faster, which raises the first-hour rating without a bigger tank. As an example, residential 50-gallon gas models in our catalog range from about 33,000 BTU/h up to 100,000 BTU/h. Before choosing a high-input model, confirm with your installer that your gas line and meter can supply it.
5. Check efficiency (UEF)
Uniform Energy Factor (UEF) is the federal efficiency rating for water heaters. Higher is better. Compare UEF only between heaters in the same usage bin (low, medium or high), which is listed on the EnergyGuide label next to the rating. Standard atmospheric tanks sit at the low end of the range. Powered damper, power vent and condensing designs can rate higher. The label also shows an estimated yearly operating cost, which is a quick way to compare two models.
6. Look at features that matter over the long run
- Warranty length. Tank and parts warranties vary by product line. For example, the Ruud Professional models we list carry an 8-year warranty. Read the manufacturer's terms; warranties usually require professional installation and proper maintenance.
- Leak detection. Some lines include a leak sensor or automatic shutoff. Our water heater shut-off valves and leak protection can add this to any heater.
- Installed top T&P valve. Some models ship with the relief valve on top, which can simplify replacing a heater that had its valve in that position.
- Height. Short and tall versions of the same capacity help with low ceilings or narrow closets.
- Low NOx. Some air districts, mainly in California, require ultra-low NOx burners. Check local rules before ordering.
7. Budget for the whole installation
The heater is only part of the job. You may also need a new gas flex connector, water connectors, a drain pan, an expansion tank, seismic straps or vent parts to meet current code. Plan for them together. See our water heater gas supplies and water heater connectors.
A quick comparison checklist
- Same vent type as the existing heater, or a planned vent change.
- Correct fuel: natural gas or propane.
- First-hour rating that meets your busiest hour.
- BTU input your gas line can supply.
- Best UEF you can afford within the right usage bin.
- Dimensions and clearances that fit the space.
- Warranty terms and the features you want.
Compare models side by side in our residential gas tank water heaters collection. It includes Rheem Professional Classic, Classic Plus and Prestige lines plus Ruud Professional models, in natural gas and propane.
Safety note: Installing a gas water heater involves gas piping, combustion air, venting and a T&P relief valve. Mistakes can cause gas leaks, carbon monoxide or scalding. Have a licensed plumber or gas fitter install it, and pull a permit where your local code requires one.
Frequently asked questions
What is the most important spec when comparing gas water heaters?
Vent type comes first, because it decides what can be installed without major work. After that, compare first-hour rating, BTU input and UEF.
Is a power vent water heater better than atmospheric?
Not by default. A power vent is useful when there is no usable chimney, or when you want to vent out a side wall. It needs electricity and has a blower that makes some noise. If your flue works, atmospheric or powered damper is often the simpler replacement.
Can I use a natural gas water heater with propane?
Only if the manufacturer offers an approved conversion kit for that exact model and it is installed by a qualified technician. Otherwise, buy the propane version.
Does a higher BTU water heater use more gas?
It burns gas faster while it is running, but it runs for a shorter time to heat the same water. Total gas use depends mostly on how much hot water you use and the heater's efficiency (UEF).