Two completely different machines that solve the same problem. A gas tankless can run a four-bathroom home in Minnesota. An electric tankless can fit in a closet in Phoenix and skip the venting bill entirely. The right call depends on your existing utilities, your climate, your hot-water demand, and how complex you want the install to be.
Below: a head-to-head comparison of the Rheem RTG/RTGH (gas) and RTEX (electric) lineups, with the cost math that decides it.
Choose gas (RTG or RTGH) if you have an existing gas line, need to serve 3+ bathrooms, live in a cold climate, or want the lowest possible operating cost in most US markets. Choose electric (RTEX) if you don't have gas service, have only 1–2 bathrooms in a warm climate, want a simpler install with no venting, or are doing a point-of-use install (single bathroom, ADU, garage). Gas wins on capacity; electric wins on install simplicity and footprint.
Maximum flow rate at 70°F temperature rise (typical mid-latitude US winter)
The pattern is clear: at any meaningful temperature rise, gas wins decisively on capacity. Even the biggest electric model (RTEX-36, 36kW) tops out around the same flow as a mid-tier gas unit (RTG-84). For cold-climate whole-home use beyond 2 bathrooms, gas is essentially the only realistic option.
The full comparison, head to head.
Natural gas or propane · 140k–199k BTU
240V whole-home · 18kW–36kW
The unit cost is the easy number to look up. The install cost is where homeowners get surprised, and it swings sharply based on what's already in place at your house.
A gas tankless needs three things: a properly sized gas line (typically 3/4" or 1" depending on run length, often larger than what an old 40-gallon tank used), an exhaust vent (metal Category 3 or PVC depending on type), and a 120V outlet for the controls. If you're replacing an existing gas tank in the same location, costs are minimal. If you're moving the unit or upgrading the gas line, costs climb fast.
Electric tankless looks deceptively simple — no gas, no vent — but the electrical demand is significant. The RTEX-24 (24kW) needs two 60A breakers and #6 AWG wire. The RTEX-36 (36kW) needs three 50A breakers and 4 AWG wire. For most older homes with 100A or 150A service panels, this means a service upgrade to 200A or higher, which can run $1,500–$3,500 on its own.
| Install Scenario | Gas (Typical) | Electric (Typical) |
|---|---|---|
| Unit cost | $800 – $1,700 | $420 – $825 |
| Like-for-like swap (existing setup adequate) | $500 – $900 labor | $300 – $600 labor |
| Vent installation | $150 – $800 | $0 |
| Gas line upgrade (if needed) | $300 – $1,500 | N/A |
| Electrical panel upgrade (if needed) | N/A | $1,500 – $3,500 |
| Dedicated breakers + heavy wire | $50 – $150 | $300 – $700 |
| Total install (best case) | ~$1,500 – $2,500 | ~$1,000 – $1,500 |
| Total install (worst case) | ~$3,500 – $5,000 | ~$5,000 – $7,000 |
Notice the spread. Electric is cheaper in the best case (no panel upgrade needed), but more expensive in the worst case (panel upgrade required). Gas is more consistent — it costs more on the low end but is less likely to surprise you on the high end.
For a typical American household using about 64 therms / 4,500 kWh worth of hot water annually, here's the rough math at average US energy prices.
| Fuel Type | Avg US Rate | Annual Cost | 10-Year Cost |
|---|---|---|---|
| Natural gas (non-condensing 0.81 UEF) | $1.50/therm | ~$120 | ~$1,200 |
| Natural gas (condensing 0.93 UEF) | $1.50/therm | ~$105 | ~$1,050 |
| Propane (condensing) | $2.50/gal | ~$220 | ~$2,200 |
| Electric (national average) | $0.16/kWh | ~$280 | ~$2,800 |
| Electric (low-rate states: ID, WA, LA) | $0.10/kWh | ~$175 | ~$1,750 |
| Electric (high-rate: CA, MA, HI) | $0.30+/kWh | ~$525+ | ~$5,250+ |
Natural gas is essentially always the cheapest fuel for water heating in the US. The picture flips toward electric only when you're comparing electric to propane in low-electric-rate states. In California or Hawaii — where electricity is expensive and natural gas access varies — running the math for your specific utility rates is critical, not optional.
Estimates are for a typical 4-person household. Your usage will vary. Check your last 12 months of utility bills for your actual consumption.
Six common situations with our honest take.
Above two bathrooms, electric simply can't keep up with simultaneous demand at any meaningful temperature rise. Gas is the only option that delivers consistent flow during peak morning hours.
40°F inlet water temperatures kill electric performance. The RTEX-36 that delivers 4.4 GPM at 70°F rise drops to 3.7 GPM at 80°F rise — not enough for two simultaneous showers. Gas handles cold inlet temps far better.
You already have the gas line, the venting pathway is in place, and a gas tankless is the most direct upgrade path. Skip the headache of a service panel upgrade — you'll save $1,500+ vs. converting to electric.
If running a new gas line costs $2,000+ and you only need to serve a couple of bathrooms in a moderate climate, electric is the simpler call. RTEX-24 or RTEX-27 handles most situations with no venting bills.
Single bathroom served by a single unit. Electric mounts in a closet, no venting through exterior wall, no gas plumbing, simpler permit. The RTEX-18 was designed for exactly this.
Phoenix, Las Vegas, Florida — high inlet water temps + modern 200A+ service panels make electric viable for whole-home use without expensive electrical upgrades.
The gas vs. electric decision is one of the fewer black-and-white calls in tankless. Tell us what you have (existing fuel, panel size, bathroom count, climate) and we'll point you at the right unit. Call 877-881-2742 — RheemTanklessOnline.com is operated by LCP Supply alongside our flagship plumbing wholesaler PlumbersCrib.com, with every order fulfilled by an authorized Rheem dealer with full manufacturer warranty support.