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COP (coefficient of performance) measures how much heat a heat pump delivers per unit of electricity it consumes — a COP of 4.0 means 4 kWh of heat for every 1 kWh of electricity. Every heat pump's COP changes with outdoor temperature: the colder it gets outside, the harder the unit works, and the lower its COP. This chart shows real, published COP and capacity figures for every APOLLO model at four standard test conditions, so you can compare cold-weather performance before choosing a model.
All figures below come from the same manufacturer test data published on each APOLLO product page — this article just puts them side by side for easy comparison across the lineup.
Heat pump COP by outdoor temperature
COP at each outdoor temperature, standard and MAX series side by side. Higher is more efficient.
| Model | COP @ 41°F (heating) | COP @ 44°F (heating) | COP @ 10°F (heating) | COP @ 95°F (cooling) |
|---|---|---|---|---|
| APOLLO 3.5 Ton | 4.6 | 3.23 | 2.11 | 4.6 |
| APOLLO 5 Ton | 4.6 | 3.35 | 2.13 | 4.6 |
| APOLLO 6 Ton | 4.6 | 3.38 | 2.11 | 4.6 |
| APOLLO MAX 3 Ton | 4.9 | 4.0 | 3.6 | 4.1 |
| APOLLO MAX 4 Ton | 4.8 | 3.9 | 3.5 | 3.8 |
| APOLLO MAX 5 Ton | 4.8 | 3.9 | 3.6 | 2.9 |
Figures are manufacturer-published COP at each standard test condition, matching the ratings shown on each product page. Real-world COP depends on your actual outdoor temperature, supply-water temperature, and distribution type.
Capacity and output by temperature
Full capacity and input-power figures at each condition, same test points as the COP chart above.
Heating: 41°F outdoor / 59°F wet bulb / 95°F to 131°F water
| Model | Capacity | Input power | COP |
|---|---|---|---|
| APOLLO 3.5 Ton | 42 KBTU | 9.2 kW | 4.6 |
| APOLLO 5 Ton | 60 KBTU | 13 kW | 4.6 |
| APOLLO 6 Ton | 71.5 KBTU | 15.7 kW | 4.6 |
| APOLLO MAX 3 Ton | 21.5 KBTU | 4.4 kW | 4.9 |
| APOLLO MAX 4 Ton | 41.6 KBTU | 8.8 kW | 4.8 |
| APOLLO MAX 5 Ton | 63.1 KBTU | 13.2 kW | 4.8 |
Heating: 44°F outdoor / approximately 114°F water
| Model | Capacity | Input power | COP |
|---|---|---|---|
| APOLLO 3.5 Ton | 35.8 KBTU | 11 kW | 3.23 |
| APOLLO 5 Ton | 47.7 KBTU | 14.2 kW | 3.35 |
| APOLLO 6 Ton | 56.3 KBTU | 17 kW | 3.38 |
| APOLLO MAX 3 Ton | 21 KBTU | 5.3 kW | 4.0 |
| APOLLO MAX 4 Ton | 38.7 KBTU | 10 kW | 3.9 |
| APOLLO MAX 5 Ton | 60.2 KBTU | 15.4 kW | 3.9 |
Heating: 10°F outdoor / 7°F wet bulb / 97°F to 106°F water
| Model | Capacity | Input power | COP |
|---|---|---|---|
| APOLLO 3.5 Ton | 22.2 KBTU | 10.5 kW | 2.11 |
| APOLLO 5 Ton | 32.4 KBTU | 15.2 kW | 2.13 |
| APOLLO 6 Ton | 39.2 KBTU | 18.6 kW | 2.11 |
| APOLLO MAX 3 Ton | 17.4 KBTU | 4.8 kW | 3.6 |
| APOLLO MAX 4 Ton | 33.6 KBTU | 9.5 kW | 3.5 |
| APOLLO MAX 5 Ton | 51 KBTU | 14.3 kW | 3.6 |
Cooling: 95°F outdoor / 54°F to 44°F water
| Model | Capacity | Input power | COP |
|---|---|---|---|
| APOLLO 3.5 Ton | 27.3 KBTU | 6.8 kW | 4.6 |
| APOLLO 5 Ton | 42.7 KBTU | 17 kW | 4.6 |
| APOLLO 6 Ton | 51.2 KBTU | 20.4 kW | 4.6 |
| APOLLO MAX 3 Ton | 4.2–19.8 KBTU | 3.2 kW | 4.1 |
| APOLLO MAX 4 Ton | 12.4–48 KBTU | 3.9 kW | 3.8 |
| APOLLO MAX 5 Ton | 15.3–60.3 KBTU | 5.3 kW | 2.9 |
MAX-series cooling capacity is published as a range because output varies with the specific hydronic configuration — see the product page for details.
Why efficiency drops in cold weather
A heat pump moves heat rather than generating it, pulling warmth from outdoor air even when that air is cold. As outdoor temperature drops, there's less heat available to extract and the compressor has to work harder to reach the same water temperature — so COP falls even though the unit still delivers heat reliably.
This is where the two APOLLO series diverge: at 10°F outdoor, standard-series COP runs roughly 2.1, while APOLLO MAX holds around 3.5–3.6 at the same condition. MAX's EVI (enhanced vapor injection) compressor technology is built specifically for higher-temperature output and steadier cold-weather performance — so the choice between series isn't only about baseboards and radiators, it's also about how efficiently the system runs through a cold winter. See the size chart for how Standard and MAX compare on capacity by square footage.
What affects real-world efficiency
The rated COP figures above are standardized test results. Your actual running efficiency also depends on:
- Supply-water temperature: lower required water temperature (radiant floors, fan coils) runs more efficiently than higher temperature (baseboards, older radiators).
- Your climate's typical winter temperature: a home that rarely sees 10°F will spend most of its season closer to the 41°F/44°F COP, not the coldest rating.
- System sizing: an oversized or undersized unit short-cycles or runs constantly at partial load, both of which hurt real-world efficiency — see the heat pump size calculator.
- Distribution type and insulation: a well-insulated home with compatible distribution lets the heat pump run at lower, more efficient water temperatures more of the time.
Checklist before comparing efficiency between models
- Compare COP at the coldest condition your climate actually sees, not just the mildest rating.
- Check the supply-water temperature your distribution system needs — it directly affects real-world COP.
- Confirm the system is sized correctly — an oversized or undersized unit rarely hits its rated efficiency.
- Ask whether MAX's cold-weather COP advantage matters for your project, even if you don't need its higher water temperature.
Frequently asked questions
What is COP for a heat pump?
COP (coefficient of performance) is the ratio of heat delivered to electricity consumed. A COP of 4.0 means the heat pump delivers 4 kWh of heat for every 1 kWh of electricity it uses — higher COP means lower running cost for the same heat output.
Why does heat pump efficiency drop in cold weather?
A heat pump extracts heat from outdoor air. As outdoor temperature falls, there's less available heat to extract and the compressor works harder to reach the same water temperature, so COP decreases even though the unit keeps delivering heat.
Which APOLLO model is most efficient in cold climates?
At the 10°F outdoor test condition, APOLLO MAX models publish COP around 3.5–3.6, compared to roughly 2.1 for standard-series models at the same condition. MAX's EVI compressor technology is built for steadier cold-weather performance.
Does a higher COP always mean lower running costs?
Generally yes for the same heat output, but the actual savings depend on your local electricity rate, how many hours the system runs at each condition, and how well the system is sized and installed. Rated COP is a standardized comparison point, not a guaranteed bill.
What's the difference between the 41°F and 44°F heating ratings?
Both are mild-weather heating test conditions at slightly different outdoor temperatures and target water temperatures — 41°F outdoor targets water up to 131°F, while 44°F outdoor targets roughly 114°F water. They're both published so buyers can compare performance at the specific water temperature their distribution system needs.
How cold can APOLLO heat pumps operate?
APOLLO's EVI compressor technology maintains reliable operation down to -31°F, well below the 10°F rating shown in this chart. The 10°F condition is a standardized comparison point, not the unit's operating limit.
Conclusion: compare efficiency at the condition that matters to you
Every APOLLO model gets less efficient as it gets colder outside — that's true of every heat pump. What matters for your project is comparing COP at the outdoor temperature your climate actually sees, and matching the series and supply-water temperature to your distribution system.
For a model matched to your home's square footage and climate, use the heat pump size calculator, or work through the full project with System Builder.
