How do you work out the right size for a ducted system?
Start with the floor area of every room you want cooled. Multiply by about 150 W per square metre. That gives the heat load if every room ran flat out.
Then size the system at about 70% of that total. Zones are never all running at full load at once, so sizing to 100% gives you a bigger, dearer unit than you need. An oversized ducted system also tends to short cycle, which wastes power and cools less evenly. Only count the rooms that will actually be zoned. Bathrooms, laundries and garages usually are not.
Is a 12.5 kW or 14 kW ducted system enough for my home?
Here is the sum for 120 m2 of zoned rooms. 120 x 150 W is 18 kW. Take 70% and you land at about 12.6 kW. That is why a 12.5 kW system suits five zones, such as four bedrooms plus an open kitchen, living and dining area.
For 130 m2 the sum is 19.5 kW, and 70% of that is about 13.7 kW. A 14 kW system suits six zones, which is the same layout plus a media room or similar.
What size split system do I need, and can one unit cool several rooms?
A single split system cools the room it is in. It will not cool the rooms behind closed doors, no matter how big the unit is. A large split in an open plan living area is a good fit. It is a poor way to cool three bedrooms down a hallway.
For one room or one open space, match the unit to the floor area, then allow for glass, insulation and how much afternoon sun the room gets. Bedrooms are usually small, so they need far less capacity than a living area. Buying a bigger unit than the room needs will not make it cool faster in any way you will enjoy, and it can leave the air feeling clammy.
Does the return air grille affect the capacity I need?
Yes. A ducted system can only deliver its rated capacity if it can pull enough air back in. An undersized return grille makes the system noisy and less effective.
As a rule of thumb, 10 to 14 kW ducted takes a 900 x 500 return grille. At 16 kW and above, it takes a 900 x 550. Ask about the return air when you compare quotes. It is easy to overlook and it matters.
How does Delta Temp size a system for a Sunshine Coast home?
For ducted, we do a free site inspection first. We measure the zoned rooms and check insulation, glass, ceiling height and orientation. Then we apply the 150 W per square metre and 70% method above and adjust for what we find. The quote is fixed after the inspection, and the cost depends mainly on system size, number of zones, brand and how hard the ductwork is to install.
We install Fujitsu and Hisense, and zone control can include AirTouch 5. Installations carry a 10 year workmanship warranty. It covers defects in our installation work only, not equipment faults, fair wear and tear or lack of servicing. Manufacturer warranties are 5 years for Fujitsu and 7 years for Hisense, parts and labour. Full terms are at deltatemp.com.au/warranty/. We are QBCC licensed and ARC authorised, and we service the Sunshine Coast from Caboolture to Noosa. Finance is available through humm, subject to approval by humm.
