Contributed by Gerry Wagner

My “Mini Split Design & Installation” curriculum has a section dedicated to properly sizing an inverter mini split. I stress that the days of walking into a room and making a statement such as, “this room is 3 tons all day long” need to be gone…GONE!

Those guesses…and lets be honest, that’s what they were…are not how someone who is a “professional” should conduct themselves. Some might think that those guesses were “educated guesses” but the reality is that they weren’t based in education at all.

Inverter mini splits are very forgiving in that they are not limited to a single BTU output like unitary, (ducted) systems. Inverter mini splits have the ability to modulate, or vary the BTU output based on both indoor and outdoor temperatures.

I know most of you who read this column aren’t in areas where boilers are used for residential heating but boilers are in my DNA as a result of growing up in this business in New Jersey and New York so I’m afraid I can’t help myself when making the following comparison.

Even though you’re not a boiler guy/gal, I’m sure you can appreciate that when it’s 50F degrees outside on a cool morning on the mountain on which I live in New York, that it is incredibly inefficient for my wife to fire up 100,000 BTUH boiler just to “take the chill off the house” as she says. A modulating boiler will balance the indoor and outdoor temperature to determine the most efficient BTU capacity and fire the boiler just to that limit…makes sense…right?

Well, an inverter mini split does EXACTLY the same thing in EXACTLY the same way.

Inverter mini splits have the ability to modulate…you are not locked into a singular capacity and output. Here is an example.

The GREE VIREO VIR24HP230V1B 2-ton single zone inverter mini split system in the COOL mode has the ability to modulate down to as little as 6,824 BTUH output and as high as 27,296 BTUH output…all out of one system!

This varied output could mask many sizing mistakes and miscues.

I stress in my training events that we all still need to use our professional skills so that we choose the correct system…and the correct system is the appropriately sized system.

I use the example of a living room with a 5,000 BTUH heat gain. The GREE VIREO VIR09HP230V1B has an operating range in the COOL mode of 3,100-9,600 BTUH and the GREE VIREO VIR12HP230V1B has an operating range of 3,100-13,000 BTUH in the COOL mode.

Now, many of us might say to ourselves, “lets choose the larger of the two,” (VIR12HP230V1B) because that’s what we were taught to do by a previous employer and/or its just what makes us feel more comfortable because we don’t trust our own sizing abilities.

The problem with this approach is that you have just priced yourself right out of the market because your competitor, who did a proper ACCA Manual J based heat gain/loss calculation, chose to quote the correct equipment, the VIR09HP230V1B and he is going to get the job!

Would the larger system have worked? Of course. The problem with this attitude is that you’re not going to get an opportunity to put your theory to work because you are not going to get the job!

We must always remember, we need to get the job…everything else flows from that!

About the Author

Gerry Wagner is the Vice President of HVAC Technical Training for Tradewinds Climate Systems. He has 38 years in the HVACR industry working in manufacturing, contracting and now training. You can contact Gerry by email: gwagner@twclimate.com and also please visit our website at www.twclimate.com.