How to size a window or through-wall air conditioner
There are six types of air conditioners: window, through-wall, portable, PTAC, split units and central air. The last three are installed by HVAC contractors, so let's focus on the two most common: window and through-wall units.
An A/C's job is to cool the room and reduce humidity. A unit that's too large cools fast but doesn't pull out enough moisture, leaving you cold, clammy and paying more than you should.
Step 1: Measure the opening and the room
Note the width and height of your window or wall opening (and the sleeve depth for through-wall units). Then multiply the room's length × width to get square feet.
Step 2: Find your BTUs
Room size (sq ft)
BTUs needed
100–150
5,000–6,000
150–250
6,000–7,000
250–300
7,000–8,000
300–350
8,000–9,000
350–400
9,000–10,000
400–450
10,000–12,000
450–500
12,000–14,000
500–550
14,000–15,000
550–600
15,000–16,000
600–650
16,000–17,000
650–700
17,000–18,000
Room size (sq ft)
BTUs needed
700–750
18,000–19,000
750–800
19,000–20,000
800–850
20,000–21,000
850–900
21,000–22,000
900–950
22,000–23,000
950–1,000
23,000–24,000
1,000–1,200
24,000–26,000
1,200–1,500
26,000–28,000
1,500–2,000
28,000–30,000
2,000–2,500
30,000–34,000
Step 3: Adjust for the room
−10%if the room is shaded
+10%if the room is very sunny
+4,000BTUs if it's in a kitchen
+600BTUs per person beyond two
Step 4: Check your circuit (this is the deciding factor)
Know your circuit's voltage (120V or 240V) and amperage (15A, 20A or 30A).
Circuit
Shared with other outlets/lights (50%)
Dedicated circuit (80%)
15 amp
7.5 A max
12 A max
20 amp
10 A max
16 A max
30 amp
15 A max
24 A max
Need a dedicated circuit for your A/C? That's a quick, common job. Request an estimate.
Guide 02
Choosing the right ceiling fan
Before you fall in love with a fan at the store, gather some information: Does the room have a fan-rated box? How high is the ceiling? What's the square footage? Is there a wall switch? What is the room used for?
Is your box rated for a fan?
A standard ceiling box supports a light fixture up to 50 lbs using its "ears." A fan-rated box adds threaded studs that support fixtures up to 150 lbs or fans up to 70 lbs. Fans are never hung from the ears: the weight and spin will loosen the screws over time. The only way to know which box you have is to partially remove the existing fixture and look.
Ceiling height
You need at least 7 feet from the floor to the lowest point of the fan. Ceilings 8 feet or lower call for a low-profile "hugger" fan; high ceilings need a downrod.
Blade span by room size
Room size
Blade span
Typical rooms
Up to 5′ × 5′
24″–36″
Bathrooms, walk-in closets, small kitchens, hallways
Up to 10′ × 10′
42″–48″
Guest rooms, kids' rooms, small offices
Up to 15′ × 15′
50″–55″
Living rooms, dens, medium offices
20′ × 20′ and up
56″+
Large rooms with 10′+ ceilings (two smaller fans often work better)
Controls & features
Two-wire switch? A remote is your best option. With three wires, you can control the fan and light separately from the wall.
Dimming: never put a standard dimmer on a two-wire fan circuit. It dims the motor too, causing a hum (that's the motor hurting).
Light kits & remotes: not every model can add them later, so decide before you buy.
Reversing motor: push air down in summer, pull it up in winter (for 8–10′ ceilings).
Guide 03
Your home's electrical service, explained
Your service is measured in amps and volts and is sized by your home's square footage, number of floors, basement and attic use, kitchen, heating and cooling, all governed by the National Electrical Code and local amendments. Common residential sizes are 60, 100 and 200 amps.
The eight parts of your service
01Utility conductors (overhead or underground)
02Your service conductors
03Conduit or cable
04Meter and meter socket
05Water main or ground rods
06Main disconnect or breaker
07Service panel (load center)
08Circuit breakers or fuses
Breakers protect property, not people
Standard breakers guard against overloads and short circuits. They won't reliably protect you from a ground fault. That's why these matter:
GFCI senses an imbalance as small as a few milliamps and protects people from shock.
AFCI detects dangerous arcing to protect equipment and property from fire.
The 80% rule: to avoid wearing out a breaker, continuous loads should use no more than 80% of its rating.
No main disconnect anywhere on your service? That usually means it's old. A service evaluation will tell you exactly where you stand.
Have an electrical issue others couldn't find?
Call Vincent directly. You'll talk to the licensed master electrician who'll actually do the work, not a dispatcher.
