A cold morning, a simple goal: steady heat without drama
Picture this: it’s 6 a.m., the street is frosted, and your old system kicks on, growls, and still can’t catch up. That’s the problem CO₂ (R-744) heat pumps were built to solve. They’re a different breed of cold-climate heat pump engineered to keep delivering heat when the temperature really drops. In this guide, we’ll walk you through what makes them tick, where they shine, and how to plan a real-world install without guesswork. We’ll keep the jargon light, but share the field notes pros use every day. If you want help sizing or planning, our Design Center is ready when you are. No fluff, just clear steps to warmer mornings.
What makes CO₂ (R-744) different and why that matters in cold air
Most heat pumps condense refrigerants at a fixed temperature. CO₂ runs a transcritical cycle above its critical point, using a gas cooler instead of a traditional condenser. That sounds fancy, but here’s the takeaway: instead of dumping heat at just one temperature, a CO₂ system can reject heat across a range, which helps it stay efficient when outdoor air is brutally cold. In plain talk, it can “lift” the temperature more easily from a very cold source to a comfortable indoor level. That’s why these units are gaining attention in northern homes and tough commercial jobs. Want to compare options while you research? Browse our air handlers key pieces in any clean, high-performing install.
Proof in the snow: real cold-weather performance
Next-gen CO₂ heat pumps have posted strong numbers in cold-climate field work. In recent trials, heating COPs landed around 1.6–2.7 below 30°F, and a median COP near 1.9 at 0–5°F. Several prototypes also held 100% of nominal heating capacity at 5°F, which cuts your reliance on electric strips or a backup furnace. Many systems continue working around -13°F (-25°C) and keep producing meaningful heat.
Why you care: steadier indoor temps, less backup heat, and fewer surprises on severe nights.
Tips from the field
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Check design heat loss at your local “1% winter design temp.” If the load is tight, consider a small buffer tank to smooth defrost events.
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Ducting matters. Restrictive returns can make any heat pump look bad in the cold.
The transcritical cycle in plain English
Think of the cycle in two zones: below the critical point, the CO₂ evaporates and picks up heat; above it, the refrigerant is “supercritical” and sheds that heat in a gas cooler across a temperature glide. That glide is the secret it lets the system match different water or air temperatures more efficiently. CO₂ is especially good at high temperature lift, like making hot domestic water from chilly inlet water. That’s why you’ll see it in heat-pump water heaters and combined space-heat/DHW packs.
Tips
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Target realistic water temps. Many homes run great with 110–130°F hydronic supply when the building shell is decent.
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Use outdoor reset. Let supply temps float down on mild days; you’ll feel the comfort and see the savings.
How CO₂ squeezes out even more efficiency
Three upgrades we like to see:
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Optimized gas-cooler pressure: Unlike standard systems, transcritical CO₂ lets the controller tune pressure for current conditions. That dynamic control is a quiet efficiency win.
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Ejectors/internal heat exchangers: These recover expansion energy and reduce compressor work lab work shows double-digit COP gains in the right conditions.
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Mechanical subcooling on HPWHs: Cold-weather water heating gets a boost—studies show ~44–57% higher COPh at low ambient temps.
Tips
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Commissioning is everything. Verify pressure targets, superheat, and pump flows.
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Mind pump curves. Oversized circulators waste power; ECM pumps dial in flow without noise.
2025 refrigerant rules: why CO₂ is a future-proof pick
Starting January 1, 2025, U.S. rules restrict refrigerants with GWP > 700 in many new HVAC applications. That nudges the market away from legacy blends like R-410A and toward low-GWP options. CO₂ (R-744) has a GWP of 1—as future-proof as it gets. In some homes, R-32 equipment is also a smart, available path right now, especially when you want a straightforward air-source system with proven parts and pricing. We stock a full range of R-32 heat pump systems to compare while CO₂ residential offerings expand.
Tip
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Planning a phased upgrade? Start with tight ducts and a right-sized air handler; refrigerant choice gets easier when the shell and airflow are dialed in.
One system, many jobs: heat, cool, and hot water
Next-gen CO₂ platforms are shifting from “a heater” to whole-home energy hubs. They can heat, cool, and make domestic hot water even simultaneously thanks to smart valving and controls. Variable-speed compressors plus predictive optimization help the unit adapt to weather swings. Some designs add thermal storage (a tank or phase-change module) so the system can pre-charge during off-peak times and coast through high-price hours.
Tips
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If you need hot water + space heat together, ask about priority logic and tank sizing.
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Zoning: Keep zones reasonable in size; tiny zones can short-cycle even smart equipment.
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Looking at ductless? See ductless mini-splits for flexible layouts.
Where you’ll see CO₂ today (and why that helps homeowners)
CO₂ is already working hard in industrial process heat (breweries, food plants, pharma), district energy, and large buildings like hospitals and hotels. Why mention that? Because tech that runs 24/7 in tough places tends to mature fast better controls, stronger heat exchangers, and clearer service procedures. That reliability and know-how trickles down to homes. If your project blurs the line between residential and light commercial say, a big hydronic retrofit or accessory dwelling with shared DHW CO₂’s temperature lift and simultaneous loads can be a fit.
Tip
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For mixed-use or multifamily, ask about central plant + distribution options. We can help compare against packaged units or multi-split layouts.
Bills and carbon: running the numbers simply
A typical high-capacity CO₂ system can deliver large volumes of hot water (think ~20,000 liters/day in commercial setups) while trimming energy by hundreds of kWh per day versus electric resistance in the right application. For homes, translate that to lower winter kWh and smaller backup heat runtime. Studies show paybacks under ~7.5 years and annual cost cuts up to ~14.5%, depending on local rates, envelope quality, and water-heating loads. The climate side is straightforward: GWP 1 refrigerant and fewer backup heat hours mean less carbon over the life of the system.
Tips
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Model first. Use your utility rates and design temp.
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Tame DHW loads. Low-flow fixtures and smart recirculation make any heat pump look like a hero.
Choosing your 2025 path: CO₂ vs. R-32 vs. dual fuel
Here’s a simple way to decide:
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CO₂ (R-744): Best when you need high temperature lift, strong DHW, and serious cold-climate performance. Great for hydronic retrofits aiming for lower supply temps.
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R-32 air-source heat pumps: Broad availability, solid efficiencies, and familiar installs. Explore R-32 systems for flexible budgets.
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Dual fuel: If your design temp is extremely low or you prefer staged risk, pair a heat pump with a high-efficiency furnace.
Tip
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Keep backup heat simple and controlled by outdoor temperature lockouts. It should assist, not steal hours from your heat pump.
Installation notes from real jobs (save these)
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Airflow first. Static pressure kills performance. Measure it.
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Hydronics: Pipe size and delta-T matter; use balancing valves.
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Defrost strategy: Make sure condensate has a path and won’t re-freeze on the pad.
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Controls: Enable outdoor reset and DHW priority if available.
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Acoustics: Flexible connectors and isolators make neighbors happy.
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Materials: Confirm line-set size/length and insulation thickness for your run.
Browse help articles. We stock accessories to tidy up the last 10% that makes systems quiet and efficient.
