Episode Summary
Executive Summary: David Roberts interviews Harvest CEO Jane Melia about a heat-pump-based home heating system that uses a hot-water thermal battery to shift electricity use to cheaper, cleaner times. Harvest integrates a CO2 heat pump water heater, a storage tank, and smart controls to decarbonize HVAC and hot water while reducing grid strain, costs, and emissions.
Main Topics: Harvest’s business and deployment stage (Priority: 5/5): Melia explains Harvest is no longer a concept: it is operating in several hundred homes, with strong customer satisfaction and a growing contractor network, mostly in California but expanding to other U.S. regions and Canada. How the thermal-battery HVAC system works (Priority: 5/5): The system replaces a gas furnace with an air handler and replaces a conventional water heater with a large hot-water tank plus a CO2 heat pump water heater outdoors, all coordinated by a Harvest pod that manages timing, temperature, and flow. Load shifting, grid value, and the duck curve (Priority: 5/5): Harvest’s central idea is to run heat pumps when electricity is cheapest and cleanest, store heat in water, and use it later for space heating and hot water, helping avoid peak demand and peaker plant use. Efficiency gains and cold-climate performance (Priority: 4/5): Beyond time-of-use arbitrage, Harvest says much of the savings come from running heat pumps at warmer times of day when they are more efficient. Melia argues the approach still works in colder climates, including cold-climate operation down to minus 25. Installation model and contractor ecosystem (Priority: 4/5): Harvest does not install systems itself; it relies on trained third-party contractors with plumbing/electrical licenses. The company emphasizes standard HVAC components, documentation, and contractor training as the scaling path. Economics, incentives, and scaling strategy (Priority: 5/5): Melia argues upfront costs are competitive after incentives, especially due to a 30% tax credit, and that long-term value comes from lower bills, avoided equipment replacement, and expanding grid flexibility markets and virtual power plant potential. Future applications and market expansion (Priority: 3/5): The conversation covers new homes, multifamily possibilities, demand-response readiness, and potential integration with larger coordinated systems, though Harvest is currently focused on single-family and small multifamily homes.
Key Arguments: Heat pumps alone can increase grid stress if everyone electrifies without storage; thermal batteries let buildings decarbonize without creating new peaks. Harvest’s tank-based thermal storage is cheaper, more durable, and simpler than adding lithium-ion batteries for thermal loads. A major share of savings comes from efficiency gains, not just time-of-use arbitrage, because the system can run heat pumps when outdoor conditions are more favorable. The system can cut emissions by shifting demand away from high-carbon peak periods and can save customers money even without ideal rate structures. By using off-the-shelf tanks and existing HVAC components, Harvest can deliver a practical retrofit solution rather than waiting for custom hardware to mature. The pod provides the intelligence layer, continuously estimating tank state, household demand, and weather to ensure comfort while optimizing energy use. Demand response and eventually VPP aggregation could add further value because each pod is already built to respond to external signals.
Data Points: Homes served: several hundred homes - Harvest is already deployed in real customers’ homes, not just in pilots. Net promoter score: close to 90% - Melia cites customer satisfaction as evidence the system works well. Geographic footprint: California, Oregon, New Mexico, Edmonton (Alberta), and planned Northeast/cold states - Current and expanding deployment regions. Tank size: 119 gallons - Standard tank used in most Harvest homes. Tank dimensions: 28 inches in diameter, about 5 feet tall - Physical size of the 119-gallon storage tank. Equivalent hot-water capacity: about 240 gallons of a regular water heater - Higher storage temperature increases effective energy density. Storage temperature: 150°F - Harvest heats stored water hotter than typical heat pump water heaters. Typical heat-pump-water-heater storage temperature: about 120°F - Used as a comparison point in the discussion. Thermal storage energy shifted: about 14 kWh - Comparable to a Tesla Powerwall in shifted thermal energy. Winter charging frequency: twice in 24 hours - Melia describes typical winter operation. Forced-air home share: about 60% to 80% - Estimate of homes suitable for ducted-system integration. Radiant-floor home share: about 5% to 10% - Another compatible home type, especially in newer homes. Refrigerant GWP (R410A): about 2000 - Used to compare climate impact of common refrigerants. Refrigerant GWP (R32): around 650 - Compared as a better but still higher-GWP option than CO2. Refrigerant GWP (CO2): 1 - Harvest’s preferred heat-pump water-heater refrigerant. Operating temperature range: down to minus 25 - Cold-climate capability of the CO2 heat pump water heater. Tax credit: 30% (Section 25D) - Harvest says the full installed system qualifies for a federal tax credit. Incremental cost vs HVAC-only heat pump: less than $1,000 more in the Bay Area - Melia claims a full Harvest system can be near parity after incentives. Home emissions share: 10% of U.S. emissions - Melia attributes this to home heating and hot water. Efficiency-driven savings share: about half - Melia says roughly half the savings come from running at more efficient times. Demand-response readiness standard: CTA 2045 / eco-port on every pod - Hardware is already prepared for external control signals. Contractor network: over 30 trained contractors - Harvest relies on trained third-party installers. Customer load-shift potential: about 90% of full heating load - Melia contrasts Harvest with smart thermostats that shift only 5% to 10%.
Pivotal Quotes: "Combine a high-performance heat pump water heater with some thermal storage and some really, really good controls." — David Roberts: Roberts summarizes Harvest’s core technical strategy after Melia explains the system. "We're able to shift basically 90% of your full heating load to whenever makes sense with zero negative impact." — Jane Melia: Melia argues the system scales because it shifts most thermal demand without hurting comfort. "Use your electrochemical batteries for your electric load, thermal storage for your thermal load." — Jane Melia: Melia’s central design philosophy for matching storage type to end use.
Implications: Harvest suggests building electrification can be cheaper and grid-friendlier if heat pumps are paired with thermal storage and smart controls. If scaled, this model could reduce emissions, avoid peak grid stress, and make thermal batteries a standard part of home energy systems.