Heating and cooling power for HVAC systems is measured in BTUs, or British Thermal Units. Similar to watt and voltage measurements for electricity, the BTU is a unit for measuring the addition and subtraction of heat from a space.
The BTUs are listed with all the other technical specifics on each HVAC system you shop for. More BTUs translates to more heating and cooling power.
As you shop, you will notice that HVAC systems have a tonnage calculation as well. The tonnage is the BTU tonnage. This is shown as BTUh, which is British Thermal Unit per hour. Many people know that 2,000 pounds is also a ton. When tons are calculated for heat, one ton is equivalent to 12,000 BTU.
Residential HVAC systems typically range from 18,000 to 60,000 BTUh. A 60,000 BTUh system is also called a five-ton HVAC system. Any system over five tons is considered a commercial system.
Most commercial systems range from two tons to 30 tons. These have a completely different structure from residential systems, which are stand-alone units. The modular nature of commercial systems means that each subsystem can be modified independently. Some commercial HVAC systems can even simultaneously heat certain parts of the building and cool another.
Estimating BTUs for Your House Size
Professional estimating methods are exceptionally reliable. Asking your HVAC installer and sales team about their estimates regarding the efficiency of your ductwork, the placement of the vents, and other details will always help you get better results.
Many homeowners also rely on a professional Manual J assessment to get detailed calculations for their HVAC needs. The Manual J will include estimate factors like:
- Sun exposure
- Family size
- Square footage
- And more
Your HVAC services professional can complete a Manual J for you. You can also get one from an energy auditor. The energy auditor will inspect your home to do the Manual J.
Professionals who calculate how much heat goes in and out at certain times also use BTUs in those measurements. They may assess things like the insular value of a window, whether the sealing around windows and doors is efficient, and how well the insulation in the walls is working. These measurements will help you assess the amount of time your HVAC system runs each day as well as the BTU requirements for the AC and furnace. In the case of the AC system, the amount of heat absorbed and taken out of the house per hour is measured in BTUh.
Getting the Right Number of BTUs
Buying a system with too many or too few BTUs causes technical HVAC difficulties. You run the risk of wearing a system out early if it is too small.
A small system is likely to run all the time without achieving the heating or cooling level the home needs. An undersized AC unit will experience strain and won’t be able to get enough electricity stored inside the capacitator, wearing things out quicker. You’ll also have a lot of noise from the system’s longer run times. Undersized furnaces may turn on and off frequently without effectiveness. In some cases, they will run 24 hours a day without heating the building up.
An oversized system will use much more energy than is advisable. It will also be highly likely to turn off before the system has completed a full cycle. The early shutoff will cause the compressor in the AC unit to turn off early, resulting in high humidity. Your air conditioner will also turn on and off constantly instead of doing a thorough job of working through the air throughout the house.
In the end, this will also wear your air conditioning unit out early. It’s important to get the right size unit!
Using Kilowatts and BTUs to Estimate Potential Energy Costs
A professional can help you estimate the amount of electricity you will use with each system you look at. The BTU calculation does help you estimate the kilowatt usage. You’ll need to consider the amount of power you have flowing through your whole house and assess the breakers and circuits to find out your capacity on a new unit.
It’s not uncommon for people to add more breakers and circuits to their home as they install HVAC systems. You may even encounter some wiring that needs to be redone to keep things efficient.
Once you’ve assessed the electrical capacity, you can start with the estimated average requirement of 20 BTUs per square foot of space inside the home. This won’t do the whole calculation in detail. However, it’s a great starting point when assessing your kilowatt usage. Many people work off the local average energy costs using this number.
Things That Will Impact Your System Requirements
One of the major influences is the ceiling height. Between houses with similar or the same square footage, the one with higher ceilings will typically have higher energy bills. Houses have been built with 8-foot ceilings as a standard measure since about 1900. But many people like higher ceilings in at least one part of the home.
You will need a larger to heat and cool the house if the ceilings reach the 12-foot range.
Windows tend to expand in size as ceilings rise, which can raise the BTU requirement for your system. Windows have a large amount of variance in regard to their insulation capabilities. It’s important to look at the SEER rating on your windows as you assess your HVAC power needs.
The SEER rating will give you a good idea regarding how much heat the window lets in and out. This includes the extra heat that comes in from direct sunlight, which can be a significant source of heat in many areas. Note that the quality of the installation on each window, whether it has damage, and the sealing condition will affect the final insulation value heavily.
The insulation values for the walls and roof are also a huge factor. Many people have sections of their home that don’t heat or cool evenly, and better insulation will help even the temperature out. The ductwork and usage of things like fans inside will also be part of the energy assessment.
TR Miller Heating, Cooling & Plumbing is a third-generation family company serving the Plainfield, IL area. We repair and install HVAC units, including mini-splits, central units, boilers, radiant heating, and furnaces. We also provide UV air filter systems, filter changes, and air handlers. Our plumbing services include slab leak repair, sump pumping, burst pipe repair, gas leak detection, toilet repair, drain cleaning, water heaters, and tankless water heater installation. We received an Angie’s List Super Service Award as well as a Customer Care Excellence Award. We have also been named an American Standard Dealer of the Year. We offer straightforward pricing for all our customers, and we work on all brands. We provide emergency repair services, and we are proud to stay up to date on the most cutting-edge technology.
Call TR Miller Heating, Cooling & Plumbing today to find out how we can help you.