Whole House Transfer Switch Guide: Complete Backup

A whole house transfer switch provides complete backup power for your entire home—no compromises on which circuits run, no load management required. When the power goes out, everything keeps working as if nothing happened.

This comprehensive guide covers everything you need to know about whole house transfer switches, from sizing and installation to the best products on the market.

What Is a Whole House Transfer Switch?

A whole house transfer switch is an automatic transfer switch (ATS) that’s rated to handle your home’s entire electrical load. Unlike partial-home solutions that only cover selected circuits, a whole house system powers everything—just like utility power.

Key Characteristics

Feature	Whole House ATS	Partial Transfer Switch
Amperage	100-400A (typically 200A)	30-60A
Circuits covered	All	6-12 selected
Generator required	16kW+ standby	3-12kW portable
Operation	Fully automatic	Manual or semi-auto
Cost	$8,000-$20,000	$500-$2,000

How It Works

1. Normal operation - Home runs on utility power through the ATS
2. Power failure detected - ATS senses loss within seconds
3. Generator starts - ATS sends start signal to standby generator
4. Transfer occurs - After generator stabilizes (~10-30 sec), ATS switches load
5. Home operates normally - All circuits powered by generator
6. Utility returns - ATS detects stable utility power
7. Re-transfer - ATS switches back to utility after brief delay
8. Generator stops - Runs for cool-down period, then shuts off

Is Whole House Backup Right for You?

Ideal Candidates

You should consider whole house backup if:

• You experience frequent power outages (more than 2-3 per year)
• Outages in your area are often extended (several hours or days)
• You work from home and need reliable power
• You have medical equipment that requires continuous power
• You have a large home with multiple HVAC zones
• You want complete peace of mind with no compromises
• You live in an area prone to severe weather (hurricanes, ice storms)
• You have a sump pump and flooding concerns
• Property value and resale are important to you

When Partial Backup May Be Better

Consider a partial system if:

• Power outages are rare and short
• Budget is a primary constraint
• You’re comfortable with essential-circuit-only backup
• Your home is smaller with minimal HVAC
• You rent or may move soon

Sizing Your Whole House System

Electrical Service Size

Your transfer switch must match your home’s electrical service:

Service Size	Common Home Type	Transfer Switch Required
100A	Small/older homes	100A ATS
150A	Medium homes	150A ATS
200A	Most modern homes	200A ATS
320A	Large luxury homes	400A ATS
400A	Estates, large properties	400A ATS

Generator Sizing

For true whole-house backup, your generator must handle your complete electrical load. Here’s a sizing guide:

Home Size	Typical Load	Recommended Generator
1,000-1,500 sq ft	10-15kW	14-16kW
1,500-2,500 sq ft	15-20kW	18-20kW
2,500-4,000 sq ft	20-30kW	22-25kW
4,000+ sq ft	30-50kW	30kW+

Load Calculation

A proper load calculation considers all electrical loads:

Load Category	Typical Watts
Central AC (3 ton)	3,500-4,000
Central AC (5 ton)	5,500-6,500
Electric furnace	10,000-15,000
Gas furnace blower	400-800
Heat pump	4,000-7,000
Electric water heater	4,500
Electric range	8,000-12,000
Electric dryer	3,000-5,000
Well pump	1,000-2,000
Sump pump	800-1,500
Refrigerator	200-400
General lighting/outlets	3,000-5,000
Pool pump	1,500-3,000
Hot tub	5,000-7,500

Note: You don’t add all loads at 100%—load diversity factors apply since not everything runs simultaneously.

Load Management Options

If your total load exceeds your generator capacity, load management helps:

Smart load shedding:

• Automatically sheds lower-priority loads during peak demand
• Allows smaller generator to handle larger home
• Reduces equipment and fuel costs

Managed loads typically include:

• Electric water heater (delayed)
• Second AC zone (alternated)
• Pool/hot tub (deferred)
• EV charger (suspended)

Whole House Transfer Switch Types

Service-Entrance Rated ATS

These install between the utility meter and your main panel, making them the main disconnect for your home.

Benefits:

• Clean installation—no separate main breaker
• Highest capacity ratings
• Designed for this purpose

Considerations:

• Requires utility coordination
• More complex installation
• Higher cost

Load-Side ATS

These install after your main panel, switching the entire load center.

Benefits:

• Doesn’t affect utility metering
• Simpler installation
• Works with existing panels

Considerations:

• May require panel modifications
• Slightly less elegant installation
• Still requires 200A+ capacity

Top Whole House Transfer Switches

Installation Process

Pre-Installation Steps

1. Site assessment - Electrician evaluates your panel, service, and generator location
2. Load calculation - Determines generator size needed
3. Permit application - Required in most jurisdictions
4. Utility notification - May need to coordinate disconnect
5. Equipment ordering - Generator and ATS ordered (2-8 week lead time)

Installation Day(s)

Day 1: Generator installation

• Concrete pad installation (or existing pad preparation)
• Generator placement and leveling
• Gas line connection (by licensed plumber)
• Battery installation

Day 2: Electrical installation

• Transfer switch mounting
• Utility disconnect coordination
• Wiring connections
• Generator-to-ATS connection
• Panel modifications if needed

Day 3: Testing and commissioning

• System testing and calibration
• Utility transfer test
• Load bank testing
• Customer training
• Inspection scheduling

Cost Breakdown

Equipment Costs

Component	Price Range
200A automatic transfer switch	$500 - $1,500
Standby generator (16-22kW)	$4,000 - $8,000
Standby generator (22kW+)	$6,000 - $15,000
Concrete pad	$200 - $500
Gas line materials	$200 - $500
Electrical materials	$300 - $800
Total Equipment	$5,200 - $16,000

Labor Costs

Service	Price Range
Electrical installation	$1,000 - $2,500
Plumbing (gas line)	$300 - $800
Concrete work	$200 - $400
Permits and inspections	$200 - $500
Total Labor	$1,700 - $4,200

Total Project Cost

System Level	Total Cost
Entry (16kW, basic install)	$8,000 - $12,000
Mid-range (20kW, typical home)	$12,000 - $16,000
Premium (22kW+, complex install)	$15,000 - $25,000
Large home (30kW+)	$20,000 - $40,000

Ongoing Costs

Maintenance

Service	Frequency	Cost
Annual maintenance	Yearly	$150 - $300
Oil change	Yearly or per hours	$50 - $100
Air filter	Yearly	$20 - $50
Spark plugs	Every 2 years	$30 - $60
Battery replacement	Every 3-5 years	$100 - $200

Fuel Costs

Generator Size	Fuel Use (full load)	Cost per Hour
16kW	2.5-3 gal/hr (propane)	$7 - $10
20kW	3-3.5 gal/hr (propane)	$8 - $12
22kW	3.5-4 gal/hr (propane)	$10 - $14

Natural gas typically costs 30-50% less than propane per hour of operation.

Generator Fuel Options

Natural Gas

Pros:

• Unlimited fuel supply (no refilling)
• Lower operating cost
• Cleaner burning
• Most convenient

Cons:

• Requires gas line connection
• May not be available in rural areas
• Supply can be interrupted in disasters

Propane (LP)

Pros:

• Available anywhere
• Stored on-site (not dependent on infrastructure)
• Long shelf life
• Works in any location

Cons:

• Requires tank (purchase or lease)
• Must monitor and refill
• Higher per-hour fuel cost
• Tank takes yard space

Dual Fuel

Some generators run on either natural gas or propane, giving you flexibility. The generator automatically switches if one source fails.

Comparing Top Brands

Generac

Market leader with largest dealer network

Pros	Cons
Most installers/dealers	Premium pricing
Excellent parts availability	Some noise complaints
Proven reliability	Proprietary components
Wide product range

Kohler

Premium quality with quieter operation

Pros	Cons
Quietest generators	Higher price point
Commercial-grade components	Fewer dealers
Excellent build quality	Longer lead times
Strong warranty

Briggs & Stratton

Value-focused with solid reliability

Pros	Cons
Lower price point	Less brand recognition
Good reliability	Smaller dealer network
Responsive support	Fewer model options
Smart features

Champion

Budget-friendly entry point

Pros	Cons
Most affordable	Less proven long-term
Good features for price	Smaller service network
Dual fuel options

Frequently Asked Questions

Frequently Asked Questions

What size generator do I need for a whole house transfer switch?

Most homes need a 16-22kW standby generator for complete whole-house coverage. A 2,000 sq ft home with central AC typically needs 18-20kW. Larger homes or those with multiple AC units may need 22kW or more.

Can a portable generator power a whole house?

Generally no. Most portable generators (3,000-12,000W) can only power essential circuits. True whole-house backup requires a 16kW+ standby generator to handle HVAC, water heaters, and all other loads simultaneously.

How much does a whole house transfer switch installation cost?

A whole house automatic transfer switch installation costs $3,000-$15,000 total, including a 200-amp service-rated ATS ($500-$1,500), standby generator ($4,000-$15,000), and professional installation ($1,500-$3,000).

Is a whole house transfer switch worth it?

Yes, if you experience frequent or extended outages, work from home, have medical equipment needs, or live in areas prone to severe weather. The investment provides peace of mind and protects against spoiled food, burst pipes, and business interruption.

Next Steps

Ready to explore whole house backup power?

1. Assess your needs - Consider outage frequency and home size
2. Calculate your budget - Plan for $10,000-$20,000 total investment
3. Get multiple quotes - Compare at least 3 installers
4. Check references - Ask for recent installation photos and reviews
5. Plan timeline - Lead times are often 4-8 weeks