HVAC Problems Solved With Engineering Data, Not Opinions
Free calculators, diagnostic guides, and reference charts backed by ASHRAE standards, DOE data, and real engineering methodology.
Understanding Your HVAC System
A central HVAC system consists of indoor and outdoor components connected by refrigerant lines. The outdoor condenser unit releases heat extracted from your home, while the indoor air handler circulates conditioned air through your ductwork.
HVAC Calculators
Professional-grade calculators based on ASHRAE and ACCA methodologies. Size equipment correctly, estimate costs, and optimize efficiency.
AC Tonnage Calculator
Here's the deal: both could be right, or both could be wrong. AC tonnage depends on far more than square footage alone. Your climate zone, insulation qu...
Air Changes Per Hour Calculator (ACH Formula)
Great question. Air changes per hour (ACH) tells you how many times the entire volume of air in a room is replaced in one hour. For a dental office, you...
Bathroom Exhaust Fan CFM Calculator
No — that's way undersized. A 120 sq ft master bath with a shower and tub needs at least 100 CFM using the fixture count method (50 CFM for the shower +...
BTU vs SACC vs ASHRAE
BTU vs SACC vs ASHRAE --- Portable AC Ratings Explained
Ceiling Fan Size Guide
It absolutely matters — and you're asking the right question. The wrong ceiling fan size either wastes energy spinning uselessly or fails to move enough...
CFM Calculator
We get this kind of question all the time. Figuring out the right CFM (Cubic Feet per Minute) for your HVAC system is one of the most fundamental — and ...
CFM Duct Sizing Chart & Calculator
Complete CFM duct sizing charts for rigid and flex duct, plus a calculator for supply and return duct sizing. ACCA Manual D methodology explained with worked examples.
Furnace Sizing Calculator
We hear this all the time. Furnace sizing is one of the most misunderstood parts of buying a new heating system, and getting it wrong costs you in comfo...
HVAC Efficiency Standards
Federal minimum efficiency standards increased in 2023. Understanding SEER, EER, HSPF, and AFUE ratings helps you compare equipment and estimate operating costs.
| Rating | Applies To | 2023 Minimum | Excellent |
|---|---|---|---|
| SEER2 | Central AC & Heat Pumps | 13.4 - 14.3* | 20+ |
| EER2 | Central AC (peak cooling) | 10.6 - 11.7* | 14+ |
| HSPF2 | Heat Pump (heating) | 7.5 | 10+ |
| AFUE | Gas Furnaces | 80% | 95%+ |
| COP | Heat Pumps & Geothermal | — | 4.0+ |
*Varies by region (North vs South). Source: DOE 10 CFR 430.
Climate Zones & Equipment Sizing
Your climate zone determines heating and cooling loads, efficiency requirements, and equipment recommendations. IECC climate zones range from Zone 1 (hot) to Zone 7 (very cold).
Quick Sizing Guidelines
| Climate | Cooling Load | Heating Load |
|---|---|---|
| Hot (Zone 1-2) | 500-700 sq ft/ton | 25-35 BTU/sq ft |
| Mixed (Zone 3-4) | 550-700 sq ft/ton | 35-45 BTU/sq ft |
| Cool (Zone 5) | 600-800 sq ft/ton | 45-55 BTU/sq ft |
| Cold (Zone 6-7) | 700-1000 sq ft/ton | 50-60 BTU/sq ft |
These are rough estimates. Actual loads depend on insulation, windows, orientation, and occupancy. Use our AC tonnage calculator or heating BTU calculator for accurate sizing.
Typical HVAC Operating Costs
Operating costs vary significantly based on equipment efficiency, local energy rates, climate, and usage patterns. These estimates assume average U.S. electricity rates of $0.16/kWh and natural gas at $1.50/therm.
| Equipment Type | Typical Wattage | Cost/Hour | Cost/Month* | Calculator |
|---|---|---|---|---|
| Central AC (3-ton) | 3,000 - 3,500W | $0.48 - $0.56 | $115 - $170 | Calculate |
| Heat Pump (cooling) | 2,500 - 3,000W | $0.40 - $0.48 | $95 - $145 | Calculate |
| Heat Pump (heating) | 3,000 - 5,000W | $0.48 - $0.80 | $145 - $240 | Calculate |
| Gas Furnace (80k BTU) | 500W + gas | $0.90 - $1.20 | $135 - $180 | Calculate |
| Electric Space Heater | 1,500W | $0.24 | $86 - $115 | Calculate |
| Dehumidifier (50 pt) | 300 - 700W | $0.05 - $0.11 | $22 - $53 | Calculate |
| Ceiling Fan | 10 - 75W | $0.002 - $0.01 | $1 - $5 | Size Guide |
*Monthly estimates assume 8 hours/day operation. Actual costs vary based on local rates, runtime, and equipment efficiency. Use our calculators above for personalized estimates with your specific electricity rate.
Common HVAC Problems & Solutions
Many HVAC issues have straightforward causes. Check these common problems before calling a technician.
AC Not Cooling
- 1.Check thermostat is set to COOL and temperature is below room temp
- 2.Replace dirty air filter (restricted airflow is #1 cause)
- 3.Verify outdoor unit is running and not blocked by debris
- 4.Check circuit breakers for both indoor and outdoor units
Furnace Not Heating
- 1.Verify thermostat is set to HEAT and above room temperature
- 2.Check that gas valve is open (handle parallel to pipe)
- 3.Inspect pilot light or igniter for proper operation
- 4.Replace clogged filter causing limit switch trips
High Energy Bills
- 1.Dirty filters force system to work harder (change monthly)
- 2.Duct leaks can waste 20-30% of conditioned air
- 3.Old equipment (15+ years) may be half as efficient as new
- 4.Poor insulation increases heating/cooling loads
Uneven Temperatures
- 1.Check that all supply vents are open and unobstructed
- 2.Ensure return air grilles are not blocked by furniture
- 3.Adjust dampers to balance airflow between zones
- 4.Consider duct sealing or zoning system upgrade
AC Short Cycling
- 1.Oversized equipment reaches setpoint too quickly
- 2.Low refrigerant causes pressure switch trips
- 3.Frozen evaporator coil due to restricted airflow
- 4.Faulty thermostat or loose wiring connections
Strange Noises
- •Squealing: Belt slipping or motor bearings
- •Banging: Loose blower wheel or broken part
- •Clicking: Relay issues or failing compressor
- •Hissing: Refrigerant leak or duct leak
Browse by Topic
Comprehensive guides organized by subject area.
HVAC Calculators
Size your HVAC system with engineering-grade calculators
- AC Tonnage Calculator
- Air Changes Per Hour Calculator (ACH Formula)
- Bathroom Exhaust Fan CFM Calculator
Installation
Installation guides and best practices
- Bathroom Exhaust Fan Venting Options and Code Requirements
- Ceiling Fan Direction
- Cold Air Return Vents
Energy Costs
Calculate and reduce your HVAC energy bills
- How Many kWh Per Day Is Normal
- How Much Does It Cost To Run an Air Conditioner
- How Much Does It Cost To Run an Electric Heater
Refrigerants
PT charts, refrigerant types, and technical data
- How Much Refrigerant In AC Units By Tonnage
- Refrigerant Pressure-Temperature Charts
- Refrigerant Types, Properties, and GWP Chart
Common Refrigerants Reference
R-22 was phased out in 2020. Most new systems use R-410A, though R-32 and R-454B are emerging as lower-GWP alternatives.
| Refrigerant | Type | GWP | Status | Common In |
|---|---|---|---|---|
| R-22 (Freon) | HCFC | 1,810 | Phased Out (2020) | Pre-2010 AC units |
| R-410A (Puron) | HFC Blend | 2,088 | Current Standard | Most new AC/heat pumps |
| R-32 | HFC | 675 | Growing Adoption | Mini-splits, newer AC |
| R-454B | HFO Blend | 466 | 2025 Standard | Future residential AC |
| R-134a | HFC | 1,430 | Current | Auto AC, refrigerators |
GWP = Global Warming Potential (CO₂ = 1). Lower is better for the environment.View full refrigerant guides →
Why Use HVAC Solver?
Engineering Standards
Every calculator uses real methodology from ASHRAE, ACCA, DOE, and EPA. Formulas are cited and verifiable.
Real Data
Every table includes units. Every calculation shows its work. Reference data comes from manufacturer specs and industry standards.
No Sales Pitch
No product reviews. No sponsored content. Just technical information to help you make informed decisions.