Heat PumpsHeat Pump System
Atomi Smart AT2239 CA Heat Pump System
Certified ratings, sizing notes, operating tips and maintenance for this 12,000 Btu/h split-system heat pump combination.
- SEER223.9
- HSPF28.3
- Cooling12,000 Btu/h
About this heat pump system
This page documents the split-system heat pump system made up of the Atomi Smart AT2239 CA outdoor unit — AHRI certificate null.
As a matched system it is rated at 23.9 SEER2, 13.1 EER2 and 8.3 HSPF2, delivering 12,000 Btu/h of cooling (about 1 tons) and 12,749 Btu/h of heating at 47 °F.
Its inverter-driven, continuously variable compressor ramps capacity up and down to match the load, which gives steadier temperatures, better dehumidification and the highest part-load efficiency.
Specifications
| Brand | Atomi Smart |
|---|---|
| Outdoor unit model | AT2239 CA |
| SEER2 | 23.9 |
| EER2 | 13.1 |
| HSPF2 | 8.3 |
| Cooling capacity | 12,000 Btu/h |
| Heating capacity at 47 °F | 12,749 Btu/h |
| Heating capacity at 17 °F | 6,722 Btu/h |
| Compressor staging | Continuously variable |
| Refrigerant | R-32 (GWP:675 | Lower GWP) |
| ENERGY STAR cold climate | No |
| Meets peak cooling (EER2) requirement | Yes |
| Connected capability | No |
| ENERGY STAR Most Efficient | No |
How it compares with other AT2239 CA matches
The AT2239 CA has 1 certified matches. The matches with the closest efficiency are listed below.
Safety information
- Installation, refrigerant charging and electrical connection must be performed by a licensed HVAC contractor in accordance with local codes and the manufacturer's installation instructions. Many jurisdictions require a permit and inspection.
- Turn off power at the outdoor disconnect and at the main panel before opening any service panel. Capacitors can hold a dangerous charge after power is removed.
- Keep children and pets away from the outdoor unit; never insert objects through the fan guard.
- Do not operate the system with panels or the fan guard removed.
- If a gas furnace provides backup heat, make sure carbon monoxide alarms are installed on every level of the home and near sleeping areas.
Installation and sizing
Proper installation matters more than any rating on the label: field studies show that incorrect charge, poor airflow and leaky ducts can cut real-world efficiency by 30% or more. Use the checklist below when reviewing quotes for the Atomi Smart AT2239 CA.
- Load calculation
Insist on a room-by-room heat-loss and heat-gain calculation (ACCA Manual J) before choosing a size. Oversized heat pumps short-cycle, dehumidify poorly and wear out sooner; rule-of-thumb sizing by square footage is unreliable.
- Verify the matched system
Confirm the outdoor unit, indoor coil or air handler (and furnace, if any) match an AHRI certificate. Mismatched components can lower efficiency well below the published ratings and may void rebates.
- Outdoor unit placement
Set the condenser on a level pad raised above expected snow depth, with at least 12–24 in. of clearance around the coil and 5 ft above the fan. Avoid spots under roof drip lines where ice can fall onto the unit.
- Ductwork and airflow
Have the contractor measure static pressure and set blower airflow (typically 350–450 CFM per ton). Leaky or undersized ducts are the most common reason a new system underperforms.
- Line set and charge
The refrigerant line set should be pressure-tested, evacuated to 500 microns or lower and charged by weight and verified by subcooling or superheat as the manufacturer specifies.
- Commissioning
Ask for a commissioning report showing airflow, refrigerant charge readings, thermostat configuration (including auxiliary-heat lockout) and a test of defrost operation.
Using your heat pump
Thermostat settings
Pick a comfortable setpoint and leave it. Heat pumps are most efficient when they hold a steady temperature; deep night setbacks in heating mode can trigger expensive auxiliary (strip) heat during recovery. If you use setbacks, limit them to 2–3 °F or use a thermostat with adaptive recovery designed for heat pumps.
Heating mode and defrost
In cold, damp weather frost builds up on the outdoor coil. The unit periodically reverses into a defrost cycle for a few minutes — you may see steam rising from the outdoor unit and hear a whoosh when the reversing valve shifts. This is normal.
Heating output drops as outdoor temperature falls. Below the system's balance point a backup heat source (electric strips or a furnace) supplements the heat pump; your installer should set the thermostat so backup heat runs only when needed.
Cooling and dehumidification
In cooling mode the inverter compressor runs for long periods at low speed, which removes humidity steadily. Long run times are normal and efficient — they are not a sign of a problem.
Care and maintenance
| When | What to do |
|---|---|
| Every 1–3 months | Check the air filter and replace it when dirty (1 in. filters usually monthly to quarterly; 4–5 in. media filters every 6–12 months). |
| Monthly in season | Keep 2 ft clear around the outdoor unit: remove leaves, grass clippings, snow and ice. Never cover the unit while it is in use. |
| Each spring | Gently hose the outdoor coil from the inside out with power off; straighten bent fins with a fin comb. |
| Each fall | Confirm the condensate drain is clear and the outdoor unit is level and not sinking into the ground. |
| Every year | Schedule professional maintenance: electrical connections, capacitor test, refrigerant charge check, coil cleaning, blower and drain service, and a defrost test. |
Troubleshooting
| Problem | Possible cause | What to try |
|---|---|---|
| No heating or cooling | Thermostat in wrong mode; tripped breaker or blown fuse; outdoor disconnect off. | Check mode and setpoint; reset the breaker once; confirm both indoor and outdoor disconnects are on. If it trips again, call a technician. |
| Steam from the outdoor unit in winter | Normal defrost cycle. | No action needed; defrost typically lasts 2–10 minutes. |
| Outdoor unit covered in ice | Defrost control or sensor fault; low refrigerant; blocked airflow; gutter dripping on unit. | Clear snow and debris; redirect dripping water. If the coil stays encased in ice for hours, switch to emergency heat and call for service. |
| Air from vents feels lukewarm in heating | Heat pumps deliver air around 90–100 °F, cooler than a furnace. | Normal. Check that the house is reaching setpoint rather than judging by air temperature. |
| High electric bills in winter | Auxiliary strip heat running too often; deep setbacks; dirty filter. | Reduce setbacks; ask your contractor to set an aux-heat lockout; replace the filter. |
| Short cycling | Oversized system; thermostat near a supply register; refrigerant or control issue. | Relocate the thermostat if needed; have the contractor verify sizing and charge. |
| Water dripping indoors | Clogged condensate drain or pump; dirty coil; frozen evaporator. | Turn the system off and clear the drain line; if ice is visible on the coil, check the filter and airflow before restarting. |
| Unusual noises (grinding, squealing) | Fan motor bearings; debris in the fan; loose panel. | Turn the system off and call a technician — continued operation can damage the compressor or motor. |
Energy use and running costs
Assuming 1,000 full-load cooling hours per year (typical of a moderate U.S. climate), this system would use roughly 502 kWh for cooling — about $85.36 at $0.17/kWh.
For heating, 1,500 full-load hours at 8.3 HSPF2 works out to about 2,318 kWh, or $394 per year, excluding any auxiliary heat. The same heat from an 80% AFUE gas furnace would cost about $359 at $1.50/therm.
Your actual cost depends on climate, home insulation, thermostat habits and local utility rates. Use these figures to compare models rather than as a bill forecast.
Frequently asked questions
What is the SEER2 rating of AHRI null?
This Atomi Smart AT2239 CA system is rated at 23.9 SEER2, 13.1 EER2 and 8.3 HSPF2.
How many tons is this Atomi Smart heat pump system?
Its rated cooling capacity is 12,000 Btu/h, which is about 1 tons (12,000 Btu/h per ton).
What refrigerant does this system use?
R-32 (GWP:675 | Lower GWP).
Can I use a different indoor unit with this outdoor unit?
Yes, but the ratings on this page apply only to this exact AHRI-certified combination. The AT2239 CA has other certified matches listed on its main page, each with its own ratings.
Sources and disclaimer
Specifications on this page come from the ENERGY STAR certified heat pumps dataset published by the U.S. Environmental Protection Agency (record certified December 2, 2024), retrieved October 7, 2026. Ratings apply only to this exact combination of components; confirm the match with the manufacturer before purchase.
The setup, operating, maintenance and troubleshooting guidance is written by ManualHarbor's editors for this specific product type and configuration. It is an independent guide — not a reproduction of the manufacturer's manual — and ManualHarbor is not affiliated with Atomi Smart. Always follow the safety instructions, installation requirements and warranty terms supplied with your unit, and contact Atomi Smart or an authorized service provider for warranty repairs and replacement parts.
Running-cost figures use assumed U.S. average utility prices and are estimates for comparison only. See our editorial methodology for details.
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