HVAC Sizing Guide

HVAC Sizing Guide

The Why and How of Sizing HVAC Equipment

Chris, the eComfort Product Expert
By 
Product Expert

If you’re always either too hot or too cold at home, you may have had the wrong-sized heating or cooling system installed. But it doesn’t have to be that way.

 

There are two main rules to knowing how to size a furnace, boiler, or air conditioner:

  1. Don’t do it yourself (unless you’re a trained pro)
  2. Make sure the trained pro you hire isn’t just guessing

Keep reading to learn what it takes to properly size your heating and cooling system. If you want a rough idea now, go straight to our HVAC sizing calculator.

Whole-House AC and Furnace Sizing

Plumber SizingHeating and cooling equipment sizing for an entire home is best done using a professional Manual J Calculation. This official calculation is put out by the Air Conditioning Contractors of America (ACCA).

An ACCA Manual J Calculation is the only trusted way to get the right-sized heating and cooling equipment for your home.

 

Any AC or furnace size calculator you find online won’t give you anything more than a guess of your home’s heating and cooling load.

 

Interestingly, that’s the same thing some contractors do. They use rules of thumb based on your home’s square footage to pick equipment that they think will work. Oftentimes, to cover themselves, they’ll oversize the equipment, which wastes energy and money down the road.

 

To maximize your comfort, we'll provide you a custom load calculation based on Manual J principles for a small fee. You can call us at 866-554-4328, or, to save time, you can pre-fill our professional sizing worksheet and send it back. If you end up buying from us, you’ll get your sizing fee reimbursed.

 

Although we still recommend having your professional installer perform a full Manual J before installation, our professional sizing will give you the closest you can get without spending tons of money.

 

There are four main factors a Manual J Load Calculation considers that many rules of thumb and cheap calculators don’t:

  1. The Local Climate: A building located in a hot and humid climate will require a larger air conditioner than an identical building located in an area with cool, dry summers. Similarly, a building in South Dakota will require a larger furnace or boiler than an identical building in South Carolina since the winters are colder in South Dakota.

  2. setting thermostatDesired Temperature: How warm or cool do you want it inside your home? As the difference between the outdoor and indoor temperature increases, there will be more heat transfer through the walls of the building, as nature always seeks equilibrium. Therefore, you need even more energy than you might think to heat a building to 75° F compared to heating it to 68° F on the same day.

  3. Building Envelope: The term “building envelope” refers to how well your home is insulated from outdoor air. This includes not only the pink stuff inside your walls, but also how energy efficient your windows and doors are. The tighter your building envelope, the less hot or cold air you will lose to the outdoors.

  4. Exterior Surfaces: Different rooms in your home will change temperature differently depending on how many exterior walls they have. For example, an interior bathroom without any exterior walls will lose less heat than a living room surrounded by three exterior walls and a ceiling.

“Rule of Thumb” guesses don’t take all these variables into account. That’s why, when it comes to furnace and AC sizing for you whole house, go with a Manual J Calculation.

 

Single-Room HVAC Calculator

If you don’t want a central heating or cooling system and are instead installing a mini split or PTAC unit, the calculation becomes much simpler. Essentially, you are now sizing for either a single-room, or multiple rooms separately. Our calculator below can help with that.

 

Use that calculator only as a guide, though. For best comfort results, you should still get a Manual J Load Calculation done, even if just for a single-room. Although you’re less likely to get a single-room application “wrong,” it can happen, so why not protect yourself?

 

Step 1. Basic Info
Step 2. Room Info
Step 3. Construction
Step 4. Results
Total Load Calculations
Start Over
Cooling Load:
Heating Load:
Basic Room & Home Information
Room Size:
Zip Code:
Room Type:
Building Age:
Download As PDF
Print
* For more accurate load calculations, you can edit the detailed information below.
Skip To Results
Tell Us About Your Home
Fill out all of the fields provided to calculate your heating and cooling loads. We'll use that information to help you find the right mini split system for your home.
Select the approximate age range of your home. We will use this to make an estimate of the quality of insulation of your home.
Because different types of rooms are used differently, they have different heating and cooling needs.
Calculate Load Estimates
Temperature Information
High: 90°F | Low: 10°F
Outdoor Design Temp. determined by ZIP Code.
Next: To Wall Details
Wall Details
Select 'Yes' if this wall separates the space being conditioned from the outdoors or an unconditioned space like a garage. Otherwise, if this wall is adjacent to another conditioned space, select 'No'.
Enter the width of the wall. If only a portion of the wall is "Exposed", enter this width.
Select 'Yes' if this wall separates the space being conditioned from the outdoors or an unconditioned space like a garage. Otherwise, if this wall is adjacent to another conditioned space, select 'No'.
Enter the width of the wall. If only a portion of the wall is "Exposed", enter this width.
Select 'Yes' if this wall separates the space being conditioned from the outdoors or an unconditioned space like a garage. Otherwise, if this wall is adjacent to another conditioned space, select 'No'.
Enter the width of the wall. If only a portion of the wall is "Exposed", enter this width.
Select 'Yes' if this wall separates the space being conditioned from the outdoors or an unconditioned space like a garage. Otherwise, if this wall is adjacent to another conditioned space, select 'No'.
Enter the width of the wall. If only a portion of the wall is "Exposed", enter this width.
Window Details
North
We assume Windows are 3'x4'. If your windows are larger or smaller, please adjust accordingly.
We assume French Doors are 3'x7'. Each half of a double door should be counted separately.
We assume Sliding Doors are 6'x7'. If your doors are larger or smaller, please adjust accordingly.
East
We assume Windows are 3'x4'. If your windows are larger or smaller, please adjust accordingly.
We assume French Doors are 3'x7'. Each half of a double door should be counted separately.
We assume Sliding Doors are 6'x7'. If your doors are larger or smaller, please adjust accordingly.
South
We assume Windows are 3'x4'. If your windows are larger or smaller, please adjust accordingly.
We assume French Doors are 3'x7'. Each half of a double door should be counted separately.
We assume Sliding Doors are 6'x7'. If your doors are larger or smaller, please adjust accordingly.
West
We assume Windows are 3'x4'. If your windows are larger or smaller, please adjust accordingly.
We assume French Doors are 3'x7'. Each half of a double door should be counted separately.
We assume Sliding Doors are 6'x7'. If your doors are larger or smaller, please adjust accordingly.
Garage Door Details
Each single garage door should be counted as 1 and each double garage door should be counted as 2.
Next: To Ceiling Details
Ceiling Details
Select 'Yes' if the ceiling separates your space from the outdoors, an attic, or any other unconditioned space. Otherwise, if there is another conditioned room above your space, select 'No'.
Enter the height of your ceiling. If you have a sloped, vaulted, or any other type of non-flat ceiling, enter the approximate average ceiling height.
Next: To Floor Details
Floor Details
Select 'Yes' if the floor separates your space from the outdoors, an unconditioned crawlspace or basment, or is a slab on grade. Otherwise, if your space is over a conditioned room, select 'No'.
Continue to Construction
Wall & Window Details
Garage Door Details
Ceiling Details
Floor Details
Previous
Submit & View Results
Basic Room & Home
Room Type
Room Size
ZIP Code
Building Age
Temperature
Edit
Avg. Outdoor Temp. High
°F
Avg. Outdoor Temp. Low
°F
Desired Indoor Cooling
°F
Desired Indoor Heating
°F
Walls
Edit
Wall Type
Wall Insulation Quality
North Wall Exposed Area
East Wall Exposed Area
South Wall Exposed Area
West Wall Exposed Area
Garage Door
Edit
# of Garage Doors
Garage Door Insulation Quality
Windows
Edit
Window Type
North Wall
East Wall
South Wall
West Wall
Ceiling
Edit
Ceiling Exposed
Ceiling Insulation Quality
Ceiling Type
Floor
Edit
Floor Exposed
Floor Insulation Quality
Floor Type
Load Results (BTU/hr)
Cooling load
Wall
Window
Ceiling
Floor
Bay
Infiltration
Internal
MRA ?
Moisture Removal Allowance: It is typical for roughly 30% of your air conditioner's capacity to be used to reduce the humidity in your home.
Total
Heating load
Wall
Window
Ceiling
Floor
Bay
Infiltration
Total
Print
Shop Mini Splits
Disclaimer: This sizing tool, although based on a version of the ACCA Manual J, is for informational use and is intended only as a guide to assist with finding the best product for your needs. Since the calculations are based on the information provided, Power Equipment Direct, Inc. assumes no responsibility for inaccuracies resulting from improperly sized equipment. For a complete, professional sizing estimate, please call us at
866-554-HEAT (4328).
+
Email My Results
Enter your email address to receive your mini split sizing results directly in your inbox.
Thank you! We will send your results shortly.
+
If you choose to start over, all of your entered information will be lost. Do you wish to continue?

 

Size Matters

Say goodbye to chills during winter and sweating during summer while saving energy and money on your heating and cooling equipment. Proper HVAC sizing using a J Load Calculation is the only surefire way to do it. Call us at (866) 554-4328 with questions.

arrow NEXT: Get a Heat Loss Calculation

Chris, the eComfort Product Expert
By 
Product Expert
Was this article helpful?