When it comes to heating and cooling your home, one of the most important factors to consider is the size of the space you need to heat and cool. The size of the space, measured in square feet, will determine how many British Thermal Units (BTUs) your HVAC system will need to provide adequate temperature control.
What is a BTU?
BTU stands for British Thermal Unit and it is a standard measurement used to determine the heating and cooling power of HVAC systems. A BTU is defined as the amount of energy needed to heat or cool one pound of water by one degree Fahrenheit. So a BTU essentially represents the amount of energy needed to change the temperature of a given amount of matter by one degree.
When it comes to HVAC systems, the number of BTUs the system provides indicates its heating and cooling capacity. The higher the BTU rating, the more powerful the system is. BTU requirements depend on the size of the space you need to heat or cool. A larger space will need a system with a higher BTU output to provide enough heating and cooling.
How Many BTUs Are Needed Per Square Foot?
As a general rule of thumb, you will need around 30 BTUs per hour for every square foot of living space in your home. This means a 700 square foot home would need an HVAC system with around 21,000 BTUs (700 sq ft x 30 BTUs) to sufficiently heat and cool the space.
However, this is just a rough estimate and your actual BTU requirements may be higher or lower depending on several factors:
- Climate – Homes in very hot or cold climates need more BTUs to cope with extreme temps.
- Insulation – Well insulated homes require less BTUs to maintain temperature.
- Windows – More/larger windows mean more heat gain/loss requiring more BTUs.
- Room height – Rooms with high ceilings need more BTUs than lower ceiling rooms.
- Sun exposure – Rooms facing south/west need more AC BTUs in summer.
- Occupants – More occupants mean more body heat requiring more heating/cooling BTUs.
Because of factors like these, it’s best to have an HVAC specialist do a thorough calculation of your home’s exact BTU needs. But for a 700 sq ft home, you can expect your unit will need around 20,000 – 24,000 BTUs to sufficiently heat and cool the space.
BTU Recommendations By Room
You can also estimate your home’s BTU needs by calculating the requirements of each room. Here are some general BTU recommendations per square footage for different rooms:
| Room | BTUs Per Square Foot |
|---|---|
| Living room | 30-40 |
| Kitchen | 30-40 |
| Bedroom | 18-30 |
| Bathroom | 18-30 |
| Dining room | 30-40 |
| Office | 18-30 |
So for example, if your living room is 300 square feet, you would need around 9,000 – 12,000 BTUs (300 sq ft x 30-40 BTUs) just for that room. Add up the requirements for each room to get a whole home estimate.
Factors That Increase BTU Needs
There are some specific factors that can increase the BTU requirements in certain rooms above the averages listed above. These include:
- Kitchens – 30-40 BTUs per square foot is for a kitchen with typical appliances. With extra appliances like double ovens, cooktops, etc you may need 40-60 BTUs per square foot.
- Family Rooms – Family rooms with big screen TVs, lots of gaming consoles, and many occupants may need 35-45 BTUs per square foot.
- Home Offices – Home offices with lots of computers, equipment, and/or poor insulation may need 35-45 BTUs per square foot.
- Bonus Rooms – Bonus rooms above a garage can require 50+ BTUs per square foot due to poor insulation.
Any room that has a lot of windows, poor insulation, and/or heat generating electronics or appliances will have higher BTU needs. This should be accounted for in your calculations.
Special Factors For Large, Open Floor Plans
Homes with large, open floor plans over 700 sq ft have some special calculations to determine total BTUs:
- For open kitchen/living/dining combo rooms over 700 sq ft, allow 40-60 BTUs per square foot.
- For very large great rooms (over 1000 sq ft) with cathedral ceilings over 15 feet tall, allow for 50-70 BTUs per square foot.
- For big open areas, increase your total BTUs by 10% for proper air circulation.
The reason these big spaces need more BTUs is because the heat/cool air needs to travel farther distances and requires greater blower fan power for proper circulation. To ensure your large open floor plan stays comfortable, plan for added BTUs.
Adjusting BTUs For Extreme Temperatures
If you live in an area with extreme summertime heat or wintertime cold, you may need to increase your HVAC system’s BTU rating:
- For areas with highs over 100°F, increase BTUs by 10-15%.
- For areas where lows reach below 0°F, increase BTUs by 10-15%.
This added capacity compensates for the extra cooling or heating needed during temperature extremes. Most HVAC contractors will make these adjustments automatically based on your local climate.
Types of BTU Systems
In addition to BTU output, you also need to consider what type of HVAC system you need for your home. The main types include:
- Furnace – Fueled by gas, oil or electricity to provide forced-air heating. Requires ductwork and between 45,000-90,000 total BTUs for average homes.
- Air Conditioner – Powered by electricity to provide forced-air cooling. Available in window units or central systems. Requires similar BTUs as furnace.
- Heat Pump – Provides both heating and cooling from one electric-powered unit. Can also extract heat from outdoor air. Requires 45,000-60,000 total BTUs.
- Boiler – Uses oil or gas to heat water and provides hydronic heating. Ideal for radiators. Sizing depends on radiator output BTUs.
Work with an HVAC pro to select the right system type and BTUs for your home’s needs. Also make sure your ductwork can handle the adequate airflow.
How Much Does BTU Output Affect HVAC Costs?
The greater your HVAC system’s BTU output, the higher both your equipment and operating costs will be. Key cost factors include:
- Higher BTU equipment has larger components that cost more.
- Installation is more labor intensive for larger, higher BTU systems, adding cost.
- Energy consumption increases with more BTU output, raising utility bills.
- Maintenance is more frequent and parts/labor are more pricey for bigger systems.
Of course, you need ample BTU output to keep your home comfortable. Focus on being energy efficient to offset costs. Get a system sized just right for your actual heating/cooling needs.
Average Installation Cost By System BTUs
| System BTUs | Average Installation Cost |
|---|---|
| 20,000 BTU | $2,500 – $4,500 |
| 30,000 BTU | $3,000 – $5,500 |
| 45,000 BTU | $4,000 – $6,500 |
| 60,000 BTU | $5,000 – $7,500 |
| 90,000 BTU | $7,000 – $10,000 |
Average Operating Cost By System BTUs
| System BTUs | Avg. Yearly Operating Cost |
|---|---|
| 20,000 BTU | $320 – $520 |
| 30,000 BTU | $400 – $640 |
| 45,000 BTU | $550 – $880 |
| 60,000 BTU | $700 – $1,120 |
| 90,000 BTU | $1,000 – $1,600 |
As you can see, both equipment and operating costs rise significantly with higher BTU systems. An accurate assessment of your home’s BTU needs can prevent overspending.
Tips For Getting The Right BTU System Size
Here are some tips to make sure your HVAC system is properly sized in BTUs:
- Have a professional do a Manual J calculation to determine your exact BTU requirements
- Calculate BTUs room-by-room then add for the total home needs
- Recalculate BTUs if finishing unfinished rooms or remodeling
- Choose variable speed (modulating) equipment for better efficiency
- Install proper insulation, air sealing, windows, etc. to prevent excessive heat loss/gain
- Locate unit centrally for optimal air distribution to all rooms
- Make sure ductwork is properly sized for BTU capacity
- Choose the highest efficiency system you can afford (SEER and AFUE ratings)
- Schedule regular maintenance to keep system operating at peak efficiency
Taking steps like these will help ensure your system provides the right amount of heating and cooling BTUs without waste.
Conclusion
When trying to determine the right HVAC system BTUs for a 700 square foot home, the typical recommendation is around 20,000 – 24,000 total BTUs. This equals roughly 30 BTUs per square foot. However, factors like room dimensions, layout, insulation, and your local climate can alter the precise BTU requirements. To properly size an HVAC system, it’s best to have an expert perform a detailed calculation of your home’s needs. This will account for all relevant variables and ensure your system has just the right amount of BTU capacity to provide optimal heating and cooling with efficiency.
