Ductwork Sizing Computation For Your HVAC: All You Need to Know

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Updated on Oct 23, 2023
5 min read
Ductwork Sizing Computation For Your HVAC: All You Need to Know

‍The power of an HVAC system may be directly proportional to its size but that does not mean that you will benefit from buying an over-sized HVAC system for your home. HVAC systems need to be adequately sized, depending on the size and area of your house. A unit that is too small for your home will have to run continuously in order to provide you the required amount of conditioned air.

This will cause unnecessary wear and tear of the components. A unit too large will keep switching Off and On, putting a load on the compressor and other parts. You will also end up spending too much on your energy bills.

a. Importance of duct size

It is not only the size of the HVAC unit that matters but also the size of your ductwork. The wrong sized ducts will cause similar problems like those caused by the wrong sized unit, eventually putting too much pressure on your unit.

Duct sizing depends on multiple factors like size of your home, air flow velocity, friction loss and static pressure of the HVAC system.

b. Square footage of your home

The size of your duct work depends not just on the size of your entire house but also on the size of each individual room. Thus, one needs to gauge the square footage of the entire house as well as that of all the different rooms in order to decide duct work sizing.Calculating the square footage of your whole house could be complicated so it is best left to an HVAC expert.

c. Cubic Feet Per Minute (CFM)

Cubic Feet Per Minute determines the velocity of air required to heat or cool each room of your house. The air velocity or air flow is directly proportional to the size of the duct work. Hence it is imperative to find the CFM of each room before deciding the size of ducts to be installed.CFM calculation requires the size of your HVAC unit in tons to be multiplied by 400 (the average output of an HVAC unit). The total must then be divided by the square footage of your house.

d. Friction loss rate of ducts

The air flow from your system also depends on the rate of friction loss of ducts. By checking this rate, contractors can understand the static pressure for your HVAC unit, throughout the length of the ductwork.

Friction loss rate in turn, depends on multiple factors like the length of each duct, the number of coils, filters, dampers, grills and registers and also the number of turns in the ductwork.

Although online friction loss calculators are available, getting to this number is a complicated process and professional contractors are best equipped to calculate this.

e. Calculators for HVAC duct sizing

The right sized HVAC unit and ducts are responsible for comfortable indoor environments.

HVAC professionals make use of elaborate tools and calculators to gauge house and duct size, giving you accurate numbers. This is safer than home owners calculating everything by themselves. Plus – not everyone is that exceptional at math!

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