Water Heater Types - Gas vs Electric vs Heat Pump vs Tankless

Why this matters

The water heater replacement is the single highest-volume major plumbing job - every house gets one every 10 - 15 years. Customer cost ranges from a modest four-figure tank swap to a much larger install for tankless or heat pump, depending on type. The right answer depends on fuel availability, electrical capacity, space, hot-water demand pattern, climate, + budget - variables the customer can't navigate alone. The plumber who walks the customer through tradeoffs closes the right job + has a happy customer for 12 years; the plumber who installs whatever's on the truck creates the customer who calls a competitor at the first hot-water complaint.

Type comparison overview

Gas tank water heater (still dominant)

Gas burner heats tank from below; flue exhausts outdoors. Sizing: 40 gal (1 - 2 person), 50 gal (3 - 4), 75 gal (large family); recovery rate matters. Variants: atmospheric vent (older, natural draft, ~60% EF), power vent (induced-draft, PVC flexible venting, ~65% UEF), direct vent / sealed combustion (best for tight homes), condensing (95%+ UEF, requires condensate drain). Best for: gas available, large demand, budget-constrained. Not ideal: no gas, tight home, electrification-focused, very small household.

Electric tank water heater

Two resistance elements (upper + lower) heat tank. 30 - 80 gal residential; slower recovery than gas. Standard 4500W on 240V/30A. Smart WiFi adds remote scheduling at small premium. High-efficiency 0.95 UEF. Best for: no gas, low demand, in-place replacement. Not ideal: high demand or high-electric-rate region.

Heat pump water heater (hybrid)

Refrigeration cycle pulls heat from ambient air to tank; uses 1/3 to 1/4 electricity of resistance. UEF 3.0 - 4.0. Hybrid has resistance backup for high demand. Sizing: 50 - 80 gal (slow recovery needs larger tank). Requirements: 1,000 cu ft room or duct outside, 40 - 90°F ambient, condensate drain, 50 - 60 dB (not for bedroom adjacency), 4 - 6°F room-cooling effect. Best for: garage/basement/utility, climate-suitable, electrification + rebate eligible. Heat pump water heaters qualified for the 25C credit while it ran, at 30% up to a per-item federal cap. 25C terminated for property placed in service after December 31, 2025, so confirm the current federal status before you put a credit on a quote. State and utility rebates are a separate track, are still widely available, and in many territories are now the larger number.

Gas tankless

Water flows through heat exchanger; gas fires on demand; continuous hot water. Sizing by GPM at desired temp rise - whole-house typically 7 - 10 GPM, two-shower simultaneous 10+. Non-condensing 80 - 85% EF needs Category III stainless venting; condensing 92 - 98% EF uses PVC (the 2025 standard). Requirements: 3/4" or 1" gas line + adequate pressure, intake/exhaust 1" - 4", 120V dedicated outlet, annual descale (voids warranty if skipped). Best for: gas available, endless-hot-water customer, small finished space, peak demand low. Not ideal: simultaneous high demand, undersized gas line.

Electric tankless

Resistance heats on demand. Do the load math before you say a word about price, because it is the deal-breaker on most houses. Amps = kW × 1000 / 240. An 18 kW unit draws 75 A. A 27 kW draws about 113 A. A 36 kW draws 150 A, and that is before the 25 percent continuous-load adder. That is why whole-house electric tankless is never "two circuits": depending on the model it lands on two, three, or four dedicated 40 - 60 A circuits, plus a service and panel that can carry the whole block at once. Count the circuits off the unit's own spec sheet, not off a rule of thumb. Most existing homes cannot support it without a service upgrade. Point-of-use (2 - 12 kW) common for under-sink + supplemental. Best for: vacation home/cabin without gas, point-of-use boost. Not ideal: whole-house in typical home, high-electric region.

Solar + indirect (niche)

Solar thermal: roof panels heat antifreeze loop to tank; the highest install cost of any option here, best suited to sun-rich climates with high water bills. Indirect: hot water from boiler through coil in storage tank; common in radiant homes; a more modest install cost than solar thermal.

Right-fit decision framework

Customer says → Recommendation

• "Gas water heater died, just want it replaced fast" → Gas tank, condensing if gas line sized
• "We're electrifying the house, removed gas service" → Heat pump
• "Small basement unfinished space, never run out of hot water" → Gas tankless if gas available; heat pump if not
• "Tiny utility closet, no room for tank" → Tankless (gas or electric POU)
• "I want lowest operating cost regardless of upfront" → Heat pump
• "I want simplest install, lowest upfront" → Standard tank (gas or electric per available fuel)
• "Vacation home unused 9 months" → Standard tank with vacation timer
• "Lots of bathrooms, simultaneous showers, family of 6" → 75 - 80 gal gas tank OR multiple tankless OR mid-tank with hybrid heat pump
• "Old house, hot water at fixtures takes 30 sec" → Recirculation pump add to any system

Install considerations

All types:

• Code-required expansion tank (most jurisdictions, on closed systems)
• T+P relief valve must discharge to safe location
• Drain pan with discharge for leaks (above-finished-floor installs)
• Service shutoffs on inlet + outlet
• Dielectric unions if mixed metals
• Combustion air for gas (varies by jurisdiction)
• Earthquake straps in CA + similar zones

Tankless-specific:

• Gas line sizing verification (often must upsize)
• Venting (sealed combustion direct-vent ideal)
• Annual descale service

Heat pump specific:

• Condensate drain (gravity or condensate pump)
• Room volume verification (1,000+ cu ft OR duct to outdoors)
• Vibration isolation
• Sound consideration

Service intervals

• Standard tank: anode rod inspection at 5 yr, replace at 8 yr; sediment flush annually; T+P test annually
• Tankless: annual descale (white vinegar OR commercial descaler); filter cleanup; combustion analysis on gas; venting inspection
• Heat pump: filter cleaning quarterly; condensate drain clearing; refrigerant level check (rare); compressor noise monitor

References

• Energy Star Water Heater database
• IRA tax credit eligibility (current year)
• AHRI water heater performance directory
• DOE Federal Minimum Efficiency Standards
• Manuall internal: Tankless Water Heater Annual Service, Install Tankless Water Heater, Water Heater Annual Service