In these tankless water heater for basement reviews we score four models, two indoor gas units and two electric units, on how well they fit a basement: vent and drain needs, efficiency, flow to upstairs bathrooms and resilience in a cool, sometimes damp space.
All four were scored on the same criteria using manufacturer specifications and owner feedback. For our shortlist see the best tankless water heater for basement guide; our Editorial Policy explains how we work. Gas units require licensed installation and CO alarms.
Top 3 Basement Tankless Heaters From Our Reviews
Rheem RTGH-90DVLN-3 9.0 GPM Condensing Natural Gas Tankless (Indoor)
- Condensing
- 9.0 GPM
- Freeze protection
Eemax HA036240 36kW 240V Electric Tankless Water Heater
- 36kW
- No vent
- Compact
Rheem RTG-70DVLN-3 7.0 GPM Natural Gas Tankless (Indoor)
- 1/2″ gas line
- 7.0 GPM
- Direct vent
As an Amazon Associate we earn from qualifying purchases.
How We Scored Basement Tankless Heaters
| Criterion | Weight | What we look at |
|---|---|---|
| Basement fit | 30% | Venting, condensate, footprint |
| Flow to the house | 25% | GPM for upstairs fixtures |
| Efficiency | 20% | UEF or thermal efficiency |
| Resilience | 15% | Freeze protection, build |
| Install demands | 10% | Gas line or breakers |
| Water heater | Score | Best for |
|---|---|---|
| Rheem RTGH 9.0 GPM | 9.0/10 | Most basement installs |
| Eemax HA036240 | 8.5/10 | Electric homes, no vent |
| Rheem RTG 7.0 GPM NG | 8.3/10 | Simple gas retrofit |
| MIZUDO EQUIK 24 | 8.0/10 | Tight finished basements |
Basement Tankless Heaters Compared
| # | Product | Key Features | |
|---|---|---|---|
| 1 |  Rheem RTGH-90DVLN-3 9.0 GPM Condensing Natural Gas Tankless (Indoor) |
| Check Latest Price |
| 2 |  Eemax HA036240 36kW 240V Electric Tankless Water Heater |
| Check Latest Price |
| 3 |  Rheem RTG-70DVLN-3 7.0 GPM Natural Gas Tankless (Indoor) |
| Check Latest Price |
| 4 |  MIZUDO EQUIK 24 24kW 240V Electric Tankless Water Heater |
| Check Latest Price |
As an Amazon Associate we earn from qualifying purchases.
1. Rheem RTGH-90DVLN-3 9.0 GPM Condensing Natural Gas Tankless (Indoor)
Highest Overall Score: 9.0/10
- Condensing, UEF 0.93
- 9.0 GPM for 3–4 showers
- Built-in freeze protection
- Ultra-low NOx, direct vent
- Digital control ±1°F
- Condensate drain needed
- Natural gas only
- Fuel: natural gas
- Flow: 9.0 GPM
- Model: RTGH-90DVLN-3
The RTGH 9.0 scored highest for combining high efficiency with whole-house flow.
Freeze protection matters in unheated basements.
Who the Rheem RTGH 9.0 GPM fits best
Most basement installs.
Who should skip the Rheem RTGH 9.0 GPM
Propane homes.
As an Amazon Associate we earn from qualifying purchases.
2. Eemax HA036240 36kW 240V Electric Tankless Water Heater
Best Electric: 8.5/10
- 36kW output
- No venting or condensate
- Compact wall mount
- Made in the USA (per listing)
- Very high amp draw
- Limited listing detail
- Power: 36kW, 240V
- Model: HA036240
- Install: hardwired
Eemax’s 36kW unit is a strong electric pick where a vent route is hard to find.
Check panel capacity with an electrician.
Who the Eemax HA036240 fits best
Basements without vent paths.
Who should skip the Eemax HA036240
Smaller panels.
As an Amazon Associate we earn from qualifying purchases.
3. Rheem RTG-70DVLN-3 7.0 GPM Natural Gas Tankless (Indoor)
Easiest Gas Retrofit: 8.3/10
- 7.0 GPM, 160,000 BTU
- 1/2″ gas line compatibility (per Rheem)
- Hot-start programming
- Universal venting compatibility
- Non-condensing, UEF 0.82
- 2–3 showers
- Fuel: natural gas
- Flow: 7.0 GPM
- Model: RTG-70DVLN-3
The RTG 7.0 often works with existing gas lines, which can simplify a tank replacement.
It suits mid-size homes.
Who the Rheem RTG 7.0 GPM NG fits best
Tank replacements on smaller gas lines.
Who should skip the Rheem RTG 7.0 GPM NG
Large households.
As an Amazon Associate we earn from qualifying purchases.
4. MIZUDO EQUIK 24 24kW 240V Electric Tankless Water Heater
Best Slim Electric: 8.0/10
- 24kW, slim 3.58″ depth
- Filter, template and mounting hardware included
- 98% heating efficiency (per maker)
- Flow figure is at a small 27°F rise
- Newer brand
- Power: 24kW, 240V
- Model: EQUIK 24
- Size: 17.05 x 12.91 x 3.58 in
MIZUDO’s slim unit fits between studs or in a finished basement closet.
Real flow drops with cold groundwater.
Who the MIZUDO EQUIK 24 fits best
Tight finished basements.
Who should skip the MIZUDO EQUIK 24
Cold northern homes.
As an Amazon Associate we earn from qualifying purchases.
Basement Tips
- Mount units off the floor in flood-prone basements.
- Use a condensate pump if there is no floor drain.
- Insulate hot lines to upper floors.
- Keep CO alarms working near gas appliances.
Frequently Asked Questions
Which basement tankless heater scored highest?
The Rheem RTGH 9.0 GPM scored 9.0/10.
Do basement units need freeze protection?
It helps in unheated basements.
Is electric easier in a basement?
It avoids venting but needs strong electrical service.
Can I reuse my tank’s vent?
Usually not; tankless units need their specified venting.
Final Verdict: Tankless Water Heater for Basement Reviews
The Rheem RTGH 9.0 GPM is the best basement tankless heater we scored. The Eemax HA036240 is the best electric model, and the Rheem RTG 7.0 GPM is the easiest gas retrofit.
Overall: Rheem RTGH-90DVLN-3 9.0 GPM Condensing Natural Gas Tankless (Indoor) Check Latest Price
Electric: Eemax HA036240 36kW 240V Electric Tankless Water Heater Check Latest Price
Gas retrofit: Rheem RTG-70DVLN-3 7.0 GPM Natural Gas Tankless (Indoor) Check Latest Price
Choose the vent and drain plan first, then the heater.
Looking for something else? Browse all of our Water Heaters guides and the wider Heating & Cooling section.
As an Amazon Associate we earn from qualifying purchases.
Write Your Review
No reviews yet. Be the first to share your experience!