Normally a Ductless heat pump heats and cools 1 area of your home so if you’re planning on conditioning multiple rooms each room will have to be sized to decide which unit to buy for each area.
So how do you size each room?
We will give you some general guidelines that you can use to help predict what size unit you will need to purchase however “ USING RULE OF THUMB TO SIZE EACH DUCTLESS HEAT PUMP IS NO REPLACEMENT FOR A PROFESSIONAL LOAD CALCULATION”. When you have a general idea of the size you need call in a licensed HVAC contractor and tell them you need a “Manual J” load calculation performed.
Before getting started you will need to know what BTU means, as you will hear it quite often when choosing the size of unit needed. BTU stands for British Thermal Unit. One BTU equals the amount of energy required to cool or heat one pound of water by 1 degree.
These are 2 steps you can use to get a general idea on the BTU size unit each area will require:
- Calculate the square footage of the area by multiplying the width by its length.
- Multiply the area by 25. The result will give you, roughly, the BTU size output needed for each area.
Here is a shortcut to size the BTU needed per square footage calculated.
*12,000 btu = 600 sq. ft
*18,000 btu = 900 sq. ft
*24,000 btu = 1200 sq. ft
*These estimates are for best case scenario being a square room w/ 8′ ceilings, no windows and in a 72-degree climate. Of course, many other factors affect the coverage area.
Remember these couple of steps only give you a general idea of the ductless heat pump size you need for each area. The MANUAL J, professional load calculation, takes in a wide range of factors to determine the correct size needed. Here are some factors that the Manual J takes into consideration:
- The square footage of the room, not counting any closets.
- The number of doors the area has.
- The number of windows the area has and if the windows are single pane glass or double pane insulated windows.
- How well the area is insulated.
- The height of the ceilings.
- The climate of the area you live in.
- How much direct sunlight and how long each area gets direct sunlight.
- Are there any additional heat sources in the room, including how many lightbulbs and their type.
- Is the room attached to the kitchen space or near the kitchen?
- How many occupants will be in each area?
- The type of flooring does each area have: hardwood or carpet?
- What temperature do you want to keep the area at during the heat of summer and the cold of winter?
So how do the above factors effect the sizing of the required unit? Here are a couple of examples:
If your ceilings are above 8’ in height you have to increase your estimated BTU by around 20%.
If the room is poorly insulated you should increase the estimated BTU by 30%.
If the climate you live in often exceeds 90 degree you will increase your estimate by 30%.
These are just a couple of examples of how the extra factors can change the unit size versus only looking at the square footage.