Air-to-water heat pumps are still rare in the US market. Air-to-air dominates because most American homes have ducted forced-air systems.
But hydronic distribution is the European default, and the engineering case for it grows stronger as we electrify heating. Lower water temperatures mean higher COPs, and radiant floors deliver comfort at temperatures that no forced-air system can match.
LG's Therma V is the most commonly specified air-to-water unit in North American Passive House and Pretty Good House projects. This review covers the R32 monobloc and split variants, real installation data, and where Therma V wins versus competing systems from NIBE, Daikin, and Bosch.
How an Air-to-Water Heat Pump Works
The Therma V outdoor unit operates the refrigerant cycle and transfers heat to a water loop. The water loop then distributes heat through radiant floors, fan coils, or low-temp radiators, and also makes domestic hot water (DHW) through an indirect tank.
This is fundamentally different from an air-to-air heat pump. Air-to-air moves refrigerant to indoor coils where a fan blows air across them. Air-to-water moves refrigerant only as far as a heat exchanger inside the outdoor cabinet (monobloc) or just inside the building (split), then distributes heat as water.
Why hydronic distribution matters
The COP of any heat pump depends heavily on the temperature lift it has to produce. A unit making 95°F water for radiant floors needs to lift heat from outdoor air (say 30°F) to 95°F — a 65°F lift.
The same unit making 130°F water for high-temp radiators or fan coils has to do an 85°F lift, and the COP drops by 30-40%.
PHIUS Passive House design standards, 2024 recommends water temperatures at or below 100°F (38°C) for hydronic distribution to maximize seasonal COP. Radiant floors operating at 85-95°F (29-35°C) are the sweet spot.
Therma V Product Lineup
LG sells three Therma V configurations in North America:
Monobloc (R32)
The complete refrigerant circuit lives outdoors. Only insulated water pipes enter the building.
Available in 7, 9, 12, 14, and 16 kW heating capacities. Single-phase 230V to 12 kW, three-phase 208/460V for 14 and 16 kW.
The monobloc approach simplifies installation because no HVAC technician with EPA refrigerant certification is needed for the indoor work. A licensed plumber and electrician can complete the install.
Split (R32)
The compressor and outdoor heat exchanger sit outside. The water heat exchanger and circulator pump live indoors.
Available in the same 7-16 kW capacities. The split design slightly improves cold-climate performance because the indoor water side doesn't need freeze protection circulators or glycol.
Hydrosplit (R290)
LG's newest configuration uses R290 (propane) refrigerant for higher temperatures and ultra-low GWP. The outdoor cycle terminates at a small refrigerant-to-water exchanger close to the wall, and water lines run inside.
R290 supports water temperatures up to 160°F (75°C), making the Hydrosplit suitable for radiator retrofits where lower-temperature systems would struggle.
Per Eurovent certification database, 2023, R290 Therma V units carry the A+++ energy label at low-temp distribution.
Performance Data
NEEP doesn't currently list air-to-water heat pumps in its cold-climate database (which is air-to-air focused). For Therma V performance data, the authoritative source is the European Keymark Heat Pump database, 2024 maintained by EU.BAC.
Published Keymark COP for the LG Therma V Monobloc 12 kW (HU121MA U33):
| Outdoor Temp / Water Temp | COP |
|---|---|
| +7°C / 35°C (radiant) | 4.45 |
| +7°C / 55°C (radiator) | 2.95 |
| -7°C / 35°C (radiant) | 2.40 |
| -7°C / 55°C (radiator) | 1.85 |
| -15°C / 35°C (radiant) | 1.80 |
The seasonal performance factor (SPF) for an average European climate using low-temp distribution comes in at 4.65 (Keymark, 2023).
Field validation
The Fraunhofer ISE Heat Pump Field Test, 2023 has measured thousands of installed heat pumps across Germany since 2010. Air-to-water units running low-temp distribution averaged a field SPF of 3.5-3.9, against lab-rated SPF of 4.5-5.0.
The ~20% real-world gap comes from defrost penalties, oversized systems running at low part-load, and DHW production at higher temperatures than space heating.
For DHW production specifically, LG Therma V units deliver COP of 2.4-2.8 when heating from cold-in (50°F) to 122°F (50°C) tank set point — competitive with dedicated heat pump water heaters like the Rheem ProTerra.
Real Installation Costs in North America
Therma V isn't a stock item at most US plumbing distributors. Pricing varies based on which regional LG HVAC distributor supplies it and whether the installer carries the LG ProDealer designation.
Recent project pricing from US installers (2024-2025):
- 9 kW monobloc, low-temp radiant, no DHW: $18,000-$22,000 installed
- 12 kW monobloc with 80-gallon indirect DHW: $24,000-$28,000 installed
- 16 kW split with buffer tank, DHW, and three zones: $28,000-$36,000 installed
The equipment cost is roughly $8,000-$14,000 of the total. The balance goes to buffer tanks, indirect water heater, manifolds, low-temp radiant or panel radiators, and labor for the hydronic distribution work.
These numbers are 50-100% higher than equivalent ducted air-to-air installations. The premium pays back through higher seasonal efficiency and a 30+ year expected service life for the hydronic distribution components.
For broader heat pump installation context, see our heat pump guide covering types, costs, and energy savings.
When Therma V Is the Right Choice
Three scenarios where air-to-water with Therma V outperforms air-to-air:
Passive House and Pretty Good House new construction
When the heating load is small (under 15,000 BTU/hr design), a radiant floor running 80-90°F handles the entire house through one slab. The Therma V can operate at peak COP almost year-round because the water temperature stays low.
The hydronic system also makes DHW from the same outdoor unit, eliminating the separate water heater. PHIUS-certified projects database, 2024 increasingly specify Therma V for this combined service capability.
Existing radiant floor retrofits
Homes built between 1990-2010 with radiant floors typically used a gas boiler delivering 120-140°F water. Replacing the boiler with a Therma V usually requires lowering the supply temp to 95-110°F, which means longer recovery times after setback but dramatically lower energy use.
Buffer tank sizing and circulator pump upgrades are usually needed. A qualified hydronic designer following ASHRAE Standard 90.1-2022, Section 6.5.4 guidance can spec the upgrades.
Multi-family and small commercial
The single outdoor unit driving multiple indoor distribution loops works well for duplexes, triplexes, and small commercial buildings. One 16 kW Therma V can serve a 4,000-6,000 sq ft well-insulated multi-family building with separate radiant zones and DHW per unit.
When Air-to-Water Doesn't Pencil
Three scenarios where air-to-air beats Therma V:
- Existing forced-air homes without hydronic infrastructure (adding radiant runs $8-15 per square foot)
- Cooling-dominated climates where condensation control on hydronic cooling adds cost and complexity
- Small budgets where the $18,000 minimum Therma V install exceeds available capital for a $8,000-$12,000 ductless alternative
Federal Tax Credits and Rebates
Air-to-water heat pumps qualify for the 25C Energy Efficient Home Improvement Credit, IRS 2024 at 30% of installed cost up to $2,000 per year, including all labor and equipment that's part of the system.
The 25D Residential Clean Energy Credit, IRS 2024 at 30% applies to ground-source heat pumps but not air-source — so Therma V uses the 25C path.
HEEHRA rebates funded by the IRA provide up to $8,000 for heat pump installations for income-qualified households, with state administration. Most states launched HEEHRA in 2024-2025, with all programs targeting full operation by mid-2026 per DOE Home Energy Rebates state launch tracker, 2025.
State rebates stack with the federal credit. Massachusetts Mass Save offers up to $10,000 for whole-home heat pump conversion. New York Clean Heat offers $1,500-$3,000 per ton of capacity for air-source heat pumps.
For a complete walkthrough of stacking incentives, see our federal energy tax credits and audit eligibility guide.
How LG Therma V Compares to NIBE and Daikin
NIBE F2120 dominates the European air-to-water market and has US distribution through Enertech Global. Daikin Altherma is the other major European player with growing US presence.
A quick lineup comparison at 12 kW nominal capacity:
| Spec | LG Therma V | NIBE F2120 | Daikin Altherma 3 H HT |
|---|---|---|---|
| Max water temp (R32) | 65°C | 65°C | 70°C |
| Rated COP (35°C/-7°C) | 2.40 | 2.55 | 2.30 |
| Seasonal COP (low-temp) | 4.65 | 4.85 | 4.50 |
| US distribution | LG ProDealer | Enertech Global | Daikin Comfort Pro |
| Typical installed cost | $24-28k | $26-32k | $25-30k |
| 10-year warranty (compressor) | Yes (registered) | Yes | Yes |
NIBE wins on raw efficiency. Therma V wins on price and distribution availability. Daikin's HT line wins for radiator retrofits needing higher water temperatures.
Pre-Installation Energy Audit Recommendations
Both BPI and Energy Star recognize air-to-water heat pumps in their cold-climate guidance. The HERS Index counts Therma V installations toward home performance scoring, and the DOE Home Energy Score weights low-temperature distribution favorably.
A Manual J load calculation is non-negotiable before specifying any air-to-water heat pump. Oversizing leads to excessive on-off cycling that destroys seasonal COP, and undersizing forces backup heat use at the worst possible time.
A BPI Building Analyst certification, 2024 or RESNET-certified auditor should also perform a blower door test to verify air sealing before final sizing. Houses with 7+ ACH50 air leakage have heating loads 20-40% higher than the building geometry alone would suggest.
If the audit reveals significant air leakage or insulation gaps, addressing those first usually downsizes the heat pump by one or two capacity steps — saving $3,000-$8,000 in equipment cost.
Frequently Asked Questions
Is LG Therma V available in the US?
Yes, but with limited distribution. LG sells Therma V through certified ProDealers, mostly in the Northeast and Pacific Northwest where hydronic systems are common. Lead times can run 8-16 weeks depending on inventory at the regional distributor. Pricing varies more than ducted equipment because installation is project-specific.
What's the difference between monobloc and split Therma V?
Monobloc keeps the entire refrigerant circuit outdoors and uses water-filled pipes to enter the building, requiring freeze protection (glycol) in cold climates. Split moves the water heat exchanger indoors, eliminating freeze concerns but requiring EPA-certified refrigerant work to commission. Monobloc is simpler and slightly cheaper to install; split offers ~5% better cold-climate efficiency.
Can Therma V do air conditioning?
Yes, but it requires a chilled water distribution system (radiant ceilings, chilled beams, or fan coils with condensate management). Standard radiant floor heating loops can be reversed for cooling only down to 65-68°F supply temp without condensation issues. Most North American Therma V installs use a separate ductless mini-split for cooling, which is simpler and cheaper.
How does Therma V handle DHW?
The Therma V outdoor unit heats an indirect water heater tank through a coil. Tank sizes range from 80 to 120 gallons depending on household demand. DHW production COP runs 2.4-2.8 because of the higher water temperature required (typically 122-130°F). LG offers a dedicated DHW priority mode that temporarily diverts all heating capacity to the indirect tank during high-demand periods.
What's the maintenance schedule for Therma V?
Annual inspection by an LG-certified installer covers refrigerant charge verification, air filter cleaning, water-side strainer cleaning, and circulator pump check. Glycol concentration in monobloc systems should be tested every 3 years. The R32 and R290 refrigerants don't need scheduled top-offs under normal operation — if charge drops, there's a leak that needs repair. Expected service life is 20-25 years for the outdoor compressor and 30+ years for the hydronic distribution.
Related Reading
- Mitsubishi Hyper Heat Cold Climate Review
- Rheem ProTerra Heat Pump Water Heater Review
- Heat Pump Guide: Types, Costs, and Energy Savings
- Best Heat Pump Brands After an Energy Audit (2026)
- Net-Zero Home Retrofits: The Complete Guide
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-- The Energy Audit Finder Team