Question 1

What is a BTU and how do I size an air conditioner or furnace?

Accepted Answer

BTU (British Thermal Unit) is the measure of heat energy. One BTU raises one pound of water one degree Fahrenheit. Air conditioning capacity is measured in BTU per hour (BTU/h); a 12,000 BTU/h air conditioner removes 12,000 BTU of heat per hour. To size an HVAC system, calculate the building's heating and cooling load using a manual J calculation: square footage × heating/cooling load factor (varies by climate zone, insulation, window area, etc.). A 2,000 sq ft house in a cold climate might need 80,000 BTU heating and 24,000 BTU cooling. Oversizing wastes energy and money; undersizing leaves the building uncomfortable and turns on emergency heat (expensive).

Question 2

What is the refrigeration cycle and how does it cool air?

Accepted Answer

The refrigeration cycle is a closed loop: (1) the compressor pressurizes refrigerant gas, heating it, (2) the condenser coil releases heat to outdoor air, liquefying the refrigerant, (3) the expansion valve throttles the liquid, dropping its pressure and temperature, and (4) the evaporator coil absorbs heat from indoor air, boiling the refrigerant back to gas. The cycle repeats continuously. This process moves heat from inside to outside, cooling the building. The amount of heat moved depends on the refrigerant flow rate and temperature difference. Understanding this cycle helps you troubleshoot low cooling (low charge, high head pressure, low evaporator temperature) and energy efficiency (high compressor discharge temperature signals inefficiency).

Question 3

How do I evacuate and charge a refrigeration system?

Accepted Answer

Evacuation (removing air and moisture) is required before first charge and after any service that opens the system. Use a vacuum pump rated for low micron (preferably 100 microns or below) and run it for 15-30 minutes, monitoring pressure with a manifold gauge set. Once evacuated to the target, isolate the pump and wait 5 minutes; if pressure holds, the system is dry. To charge, connect the refrigerant cylinder (with the gauge set) to the low side of the system, crack the valve to pressurize the gauge lines, then open the isolation valve on the system. Vapor charge (from the top of the can) fills until the target pressure is reached; liquid charge (from the bottom) is faster but risks compressor damage if done incorrectly. Document all charges and keep recovery logs per EPA regulations.

Question 4

What is the difference between static return air path and ductwork design?

Accepted Answer

Return air (air drawn back from the conditioned space to the furnace or air handler) must have a low-pressure path back to the equipment. If return air ducts are oversized or restrictive, the static pressure builds, reducing airflow and efficiency. Proper return air design uses larger ducts (lower velocity) or multiple return paths. A common mistake is installing a single small return-air duct on a two-story house; upstairs becomes pressurized and downstairs becomes negative, causing drafts and poor comfort. Return air should be sized for 0.05 to 0.10 inches of water column static pressure; anything higher indicates undersized ducts.

Question 5

What are the EPA Section 608 requirements for refrigerant handling?

Accepted Answer

The EPA (Environmental Protection Agency) requires anyone who handles refrigerants to be certified. Section 608 Certification levels are: (1) Type A: small appliances (less than 5 pounds charge), (2) Type B: high-pressure systems (air conditioning, heat pumps), (3) Type C: low-pressure systems (centrifugal chillers), (4) Core: general knowledge (required for all). Certification requires passing a test (proctored or online). You must recover and recycle refrigerant (cannot vent it); violating this law incurs fines up to $37,500 per violation. Maintain logs of all refrigerant recovered and its disposal.

Question 6

How do I balance an air conditioning or forced-air heating system?

Accepted Answer

Balancing ensures each room or zone receives its intended airflow. After installation, measure the static pressure drop across the furnace and ductwork using a manometer (or digital static gauge). If total static is too high, the furnace blower is working too hard and airflow is low. Reduce ductwork resistance by opening dampers, enlarging ducts, or reducing duct length. Next, measure airflow at key vents and dampers using a flow hood or anemometer. Adjust dampers in branches to balance flow: high-flow areas get damped more, low-flow areas get opened. Document final flow rates in each room for future reference and adjustment.

Question 7

What is the difference between forced-air, hydronic, and radiant heating?

Accepted Answer

Forced-air heating uses a furnace to heat air, which is then blown through ducts to vents in each room. It is fast (reaches comfortable temperatures quickly) but prone to temperature swings and noise. Hydronic heating uses a boiler to heat water, which is pumped through pipes to radiators or baseboard convectors. It is even, quiet, and efficient but slower to respond. Radiant heating warms surfaces (floors, walls, ceilings) via hot water tubes or electric cables; the warm surface radiates heat to the room, providing comfort without blowing air. Radiant is the most efficient and comfortable but most expensive to install. Each system has trade-offs in cost, comfort, efficiency, and maintenance.

Region	Junior	Mid	Senior
USA	$32k	$58k	$85k
UK	£21k	£39k	£58k
EU	€24k	€44k	€66k
CANADA	C$40k	C$68k	C$100k

Region	Junior	Mid	Senior
USA	$32k	$58k	$85k
UK	£21k	£39k	£58k
EU	€24k	€44k	€66k
CANADA	C$40k	C$68k	C$100k

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