Smallest Tankless Water Heaters in 2026 (Compact Gas + Electric)

The smallest electric tankless water heater in 2026 is the Bosch Tronic 3000T at just 10.5 x 7.0 x 3.2 inches — roughly the size of a hardcover book — delivering 3.4 kW for a single handwashing sink. The smallest gas model is the Rinnai V53DeN at 20.5 x 14.0 x 8.7 inches, packing 120,000 BTU/h into a unit barely larger than a carry-on suitcase.

If you need hot water in a tight space — under a sink, inside a closet, in an RV, or mounted on a cramped utility wall — these compact models deliver surprising performance from minimal footprints.

Compact Electric Tankless Water Heaters

Electric models dominate the "smallest" category because they have no combustion chamber, no heat exchanger fins, and no venting requirements. The heating elements are compact, and the housing is essentially a small junction box.

Bosch Tronic 3000T ES2.5 — Smallest Overall

At 10.5 x 7.0 x 3.2 inches and 3.5 pounds, the Bosch Tronic is smaller than most routers. It hides under a bathroom vanity or behind a utility sink panel with room to spare. The 3.4 kW draw requires a single 20A/240V circuit — one of the few tankless units that works with standard residential wiring without dedicated heavy circuits.

The limitation is obvious: 0.6 GPM at a 35F rise serves only a single handwashing faucet. This is a purpose-built point-of-use heater for commercial restrooms, office kitchens, or adding hot water to a remote sink where running a pipe from the main heater is impractical.

Installation: Mounts with two screws. Two 3/8-inch water connections (standard compression fittings). One 20A/240V circuit with #12 AWG wire. Total install time: 1–2 hours. Total cost: $250–$400 installed.

EcoSmart ECO 11 — Best Small All-Rounder

At 11.5 x 8.0 x 3.75 inches, the ECO 11 packs 13 kW into a unit the size of a laptop bag. It delivers 2.2 GPM at 35F rise — enough for a full shower in warm climates or a bathroom sink plus handwashing in cold climates.

This is the go-to model for guest bathrooms, tiny homes, garage apartments, and under-sink installations. A single 60A/240V circuit with #6 AWG wire handles the load. Lifetime warranty on the heat exchanger.

Real-world example: A homeowner in Phoenix added the ECO 11 to a detached casita (guest house) 50 feet from the main home. Instead of running a hot water line underground ($1,200–$2,000), they installed the ECO 11 on the casita wall for $650 total. Hot water at the casita faucet and shower in under 5 seconds.

Stiebel Eltron DHC 3-2 — Smallest Footprint

The DHC 3-2 measures just 7.9 x 6.5 x 2.9 inches — the most compact tankless unit available from any manufacturer. At 3.0 kW, it is designed exclusively for single-sink handwashing. The German build quality and brass fittings justify the premium over the Bosch Tronic.

Best for: High-end commercial restrooms, dental offices, medical exam rooms, and any application where a tiny footprint and reliability are paramount.

Compact Gas Tankless Water Heaters

Gas units are inherently larger because they contain a combustion chamber, heat exchanger, exhaust fan, and gas valve. The smallest gas models are still larger than the largest electric point-of-use units. However, they deliver far more heating power.

Rinnai V53DeN — Smallest Gas With Real Power

The V53DeN squeezes 120,000 BTU into a 20.5 x 14.0 x 8.7-inch enclosure, making it the smallest gas tankless that can serve a whole home in warm climates. At 5.3 GPM (35F rise) and 34 pounds, it mounts on any load-bearing wall with standard bracket hardware.

This is a non-condensing unit (UEF 0.81), requiring Category III stainless steel venting. However, the compact size and 120,000 BTU output make it ideal for condos, small homes, and retrofit situations where cabinet space is tight. Available in both natural gas (V53DeN) and propane (V53DeP).

Real-world example: A 900 sq ft condo in Miami with one bathroom and a kitchen. The V53DeN replaced a closet-hogging 40-gallon tank, freeing 6 square feet of storage space. Groundwater at 72F means only a 48F rise — the unit delivers 4.4 GPM, running a shower and kitchen faucet simultaneously with headroom.

Takagi T-H3J — Most Compact Gas Frame

At 20.3 x 13.8 x 7.3 inches, the Takagi T-H3J has the shallowest depth of any gas tankless — only 7.3 inches from wall to front. This matters in tight utility closets and between-stud installations. At 100,000 BTU and 32 pounds, it is the lightest gas model available.

The trade-off is capacity: 4.0 GPM at 35F rise limits it to single-fixture use in moderate climates and light multi-fixture use in warm climates. Best for apartments, studios, and small homes under 1,200 sq ft.

Size Comparison: Tankless vs Tank

To appreciate the space savings, here is a direct dimensional comparison:

A compact electric point-of-use unit is 97% smaller by volume than a 50-gallon tank. Even a full-size gas tankless is 70% smaller and frees 3 square feet of floor space.

Sizing Guide for Compact Units

Small does not mean inadequate if you match the unit to your demand:

Installation Considerations for Tight Spaces

Clearance Requirements

Even compact units need minimum clearances for service access and (for gas) combustion air:

Electric POU: 1 inch clearance on all sides. No combustion air needed. Can be installed in enclosed cabinets.

Gas units: Minimum 12 inches of clearance in front for service access. 1-inch clearance on sides and top. Combustion air supply per local code (usually 1 sq in per 1,000 BTU for confined spaces). Venting must maintain minimum clearances from combustible materials.

Wall Strength

Gas tankless units (32–85 lbs) need mounting on a load-bearing wall or with toggle bolts rated for 100+ lbs. Electric POU units (3–20 lbs) can mount on drywall with standard anchors.

Vibration and Noise

Gas units vibrate slightly when the burner fires (50–65 dB). Avoid mounting on shared bedroom walls. Use rubber isolation pads between the bracket and wall to reduce transmitted vibration. Electric units are nearly silent (under 40 dB).

Real-World Small-Space Examples

Example 1: NYC Studio Apartment

Space: 450 sq ft, one bathroom, no gas. Old 30-gallon electric tank consumed the only closet. Installed EcoSmart ECO 11 (11.5 x 8 x 3.75 in) on the bathroom wall behind the door. Freed the entire closet for storage. One 60A circuit from the panel (30-foot run). Total cost: $650. Monthly savings: $8 (eliminated standby loss).

Example 2: Dental Office Restroom

Need: Hot handwashing water in a restroom 60 feet from the main heater. Cold water arrived after 20 seconds of running. Installed Stiebel Eltron DHC 3-2 (7.9 x 6.5 x 2.9 in) under the sink. Instant warm water. Single 20A circuit. Total cost: $380.

Example 3: RV Hot Water Upgrade

Setup: Class C motorhome with a failed 6-gallon propane tank heater. Replaced with Eccotemp i12-LP (17.5 x 11.5 x 4.5 in) liquid propane unit. Wall-mounted in the existing water heater compartment. Delivers 3.4 GPM — enough for a camp shower and sink simultaneously. Weight savings: 22 lbs lighter than the old tank unit.

Example 4: Garage Workshop Sink

Need: Hot water at a garage utility sink for parts cleaning. No gas in the garage. 100-foot pipe run from the house heater. Installed Rheem RTEX-08 (10 x 7.5 x 3.5 in) next to the sink. Single 40A/240V circuit. Hot water in 3 seconds. Total cost: $450.

Key Takeaways

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