In HVAC, there are established recommendations of how many CFM per BTU of heating and cooling a unit should have. In most cases, we use CFM per ton. However, you can simply convert tons to BTUs to get an idea of how many CFM per BTU is adequate.
Based on this, we can convert BTU to CFM as well as CFM to BTU. Further on, you will find these two charts:
- BTU To CFM Chart. This 1st chart will tell you how many CFMs you need to adequately propagate 5000 BTU to 100,000 BTU of heating or cooling output through your home.
- CFM To BTU Chart. This 2nd chart will tell you how many BTUs of heating or cooling you can propagate through your home if your HVAC system can generate anywhere from 100 CFM to 4000 CFM or airflow.
Here are the two metrics we are dealing with:
- CFM or Cubic Feet per Minute is a measure of airflow. HVAC units like furnaces and air conditioners can produce anywhere from 100 CFM to over 4000 CFM airflow.
- BTU or British Thermal Unit is a measure of heating or cooling output. Smaller window and portable AC units can produce as little as 5000 BTU and 6000 BTU, respectively. Bigger AC units can produce well over 80,000 BTU of cooling output and big furnaces can easily produce over 100,000 BTU.
There are two HVAC rules of thumb we can use to figure out how many CFM per BTU we need:
- For 1 ton of heating/cooling, we need about 400 CFM of airflow. You can read more about CFM per ton metrics here.
- 1 ton of heating/cooling is equal to 12,000 BTU. You can read more about the ton to BTU conversion in HVAC here.
The primary reason for figuring out how many CFM you need is to get homogeneous heating or cooling output without localized hot spots.
Namely, we need 400 CFM of airflow per ton. 1 ton is equal to 12,000 BTU. That means that, in order to get the CFM per BTU, we have to divide the
CFM Per BTU = (400 CFM/Ton) / (12,000 BTU/Ton) = 0.033 CFM Per BTU
Basically, we need 0.033 CFM per BTU of heating or cooling. That is equal to 1/30 CFM per BTU.
In short, 30 BTU of heating and cooling is produced with 1 CFM of airflow; this is the BTU per CFM relationship.
Based on this CFM per BTU conversion, we can check how many CFM do differently sized HVAC units (furnaces, AC units) require:
BTU To CFM Chart
In this 1st chart, we can have a look at HVAC units with different BTU outputs and see how many CFM of airflow do they roughly need to bring that heating/cooling into our home:
|HVAC BTU Output:||Required CFMs (Airflow):|
|5000 BTU Unit||167 CFM|
|6000 BTU Unit||200 CFM|
|7000 BTU Unit||233 CFM|
|8000 BTU Unit||267 CFM|
|9000 BTU Unit||300 CFM|
|10,000 BTU Unit||333 CFM|
|11,000 BTU Unit||367 CFM|
|12,000 BTU Unit||400 CFM|
|14,000 BTU Unit||467 CFM|
|15,000 BTU Unit||500 CFM|
|18,000 BTU Unit||600 CFM|
|24,000 BTU Unit||800 CFM|
|30,000 BTU Unit||1000 CFM|
|36,000 BTU Unit||1200 CFM|
|42,000 BTU Unit||1400 CFM|
|48,000 BTU Unit||1600 CFM|
|54,000 BTU Unit||1800 CFM|
|60,000 BTU Unit||2000 CFM|
|100,000 BTU Unit||3333 CFM|
As you can see, you will need about 1000 CFM of airflow to propagate 30,000 BTU of heating or cooling output through your home.
Let’s have a look at the CFM to BTU chart as well:
CFM To BTU Chart
In this 2nd chart, we can have a look at HVAC units that produce different airflow (CFMs) and how much BTU heating or cooling output you will likely see these units producing:
|CFMs Produced (Airflow):||Estimated BTU Output:|
|100 CFM||3000 BTU|
|200 CFM||6000 BTU|
|300 CFM||9000 BTU|
|400 CFM||12,000 BTU|
|500 CFM||15,000 BTU|
|600 CFM||18,000 BTU|
|700 CFM||21,000 BTU|
|800 CFM||24,000 BTU|
|900 CFM||27,000 BTU|
|1000 CFM||30,000 BTU|
|1200 CFM||36,000 BTU|
|1400 CFM||42,000 BTU|
|1600 CFM||48,000 BTU|
|1800 CFM||54,000 BTU|
|2000 CFM||60,000 BTU|
|2500 CFM||75,000 BTU|
|3000 CFM||90,000 BTU|
|3500 CFM||105,000 BTU|
|4000 CFM||120,000 BTU|
Example: With 500 CFM airflow, your HVAC unit will be able to adequately propagate 15,000 BTU of heating or cooling output throughout your home.
With these two conversions and charts, you can now quite easily convert BTUs to CFMs and CFMs to BTUs. If you need any help with the conversion, you can use the comment section below and we will try to help you out.