The Whole-House Electrification Sequence
Why this matters
A house comes off gas one appliance at a time, usually in the order things break, and usually through whichever trade the customer happened to call. That order is the most expensive one available. The EV charger that went in first eats the electrical headroom the heat pump needed. The furnace that came out before the water heater leaves a small appliance alone in a big chimney. The heat pump sized before anyone sealed the attic is a size too big for the house it ends up in. None of those are installation mistakes. They are sequencing mistakes, and every trade that touches the house can either prevent them or cause them.
This card owns the order. The component cards (panel upgrades, heat pump water heaters, induction, EV chargers, cold-weather heat pump operation) own how each piece is done.
The order, and the one reason behind each position
- Envelope and air sealing. Everything downstream is sized to the heat loss, and this is the only step that shrinks it.
- Water heating. Moderate load, often the first gas appliance to fail, and frequently doable without touching the service.
- Space heating and cooling. The largest load that cannot be shifted in time, sized to the house step 1 left behind.
- Cooking. Big nameplate, small energy, and it runs in short bursts that a load calculation counts generously.
- Drying. Small, flexible, and now available at 120 volts.
- Vehicle charging. The largest continuous load, and the only one that can be told when to run.
The governing principle: fixed, weather-driven loads get sized first against the smallest house you can make, and flexible loads go last, onto whatever capacity is measured to remain. The gas service itself closes only after the last gas appliance is gone.
Why the envelope goes first even though nobody calls for it
Heat loss sets three numbers at once: the heat pump's capacity at the design temperature, the size of any resistance backup, and the amps that backup draws on the coldest night of the year. Cut the heat loss and all three fall together.
Resistance backup is where this lands on the electrical service. Electric resistance heat draws about 4.2 amps per kilowatt at 240 volts. A house that needs 10 kilowatts of strip heat to cover its coldest hours is putting roughly 42 amps on the service in exactly the hour when everything else is also running. A house that air sealing and attic insulation brought down far enough to need 5 kilowatts is putting about 21 amps there. That 21-amp difference is often the difference between a service that holds and one that has to be replaced.
The second effect is equipment size. A heat pump selected against the pre-retrofit load will be oversized after the retrofit, and an oversized heat pump short-cycles in mild weather and dehumidifies poorly in summer. See related: The Cycling That Wastes What the Capacity Gained.
The honest limit: envelope work does not always pencil. A tight, well-insulated house built in the last twenty years has little to gain, and a balloon-framed house with plaster walls can cost more to seal than the smaller heat pump saves. "Envelope first" means assess the envelope first: a blower door number and an attic look before anyone selects equipment. It does not mean every house gets insulation before it gets a heat pump.
Why water heating usually comes second
Three reasons, in descending order of how often they decide it.
It fails first. A tank water heater has a shorter life than a furnace, so the water heater is often the first gas appliance due for replacement. A plan that has already decided "heat pump water heater" turns that emergency into the first step instead of a like-for-like gas swap that resets the clock by a decade.
It may not need the service. A 120-volt plug-in heat pump water heater can run on an ordinary circuit. See related: Plug-In 120-Volt Heat Pump Water Heaters.
It is the easier half of the venting problem. When a gas water heater and a gas furnace share a chimney, removing the water heater leaves the furnace, the larger appliance, alone in a flue it already dominated. That still has to be checked against the venting tables, but it is the milder case. Removing the furnace first is the classic failure: the small water heater is left alone in a chimney sized for both. See related: What Removing a Gas Appliance Does to the Ones Left.
So when the order runs the other way, because the furnace died first, the venting fix for the water heater belongs in the heat pump job, not in a later visit.
Why space heating comes third and not first
It is the biggest decision and it should be made against the smallest house, which means after step 1. It also needs the measured electrical picture, which is easier to read once the water heater has changed.
In practice the trigger is often the air conditioner, not the furnace. When a central AC fails in a house with a working gas furnace, the plan's move is a heat pump in the AC's place, sized for the post-envelope load, running with the existing furnace as backup until the furnace fails. That is dual fuel, and it lets the space-heating step happen in two halves without a second coil change. See related: Backup Heat: Dual Fuel or Resistance.
Why cooking and drying sit in the middle
An induction range has a large nameplate rating and uses little energy. Under the standard dwelling calculation, a single household range up to 12 kilowatts is counted at 8 kilowatts (NEC 220.55, Column C, as adopted by your jurisdiction), which is about 33 amps at 240 volts on paper for an appliance that, in use, mostly runs one or two zones for twenty minutes. That gap between counted and used is why measured load matters so much at this step. See related: Measuring Existing Load Before You Sell a Service Upgrade. Induction conversion itself: see related: Induction Cooking Conversion Reference.
A heat pump dryer is a small load and some run at 120 volts. It goes late because it is easy, and because closing the old dryer vent is a step the house needs regardless. See related: How to Install a Heat Pump Dryer and Close the Old Vent.
Why the car goes last
An EV charger is a continuous load. A charger set to deliver 48 amps occupies 48 amps of the service for hours, every night. Installed first, it is counted at its full setting and every later load lands on a service with little left.
Installed last, it can be fitted to whatever measured capacity remains. Two tools make that possible: a lower charger setting (most chargers can be set below their maximum) and load management, where a device or an energy management system cuts the charger back when the house load rises. Under the NEC, a load controlled by a listed energy management system can be counted at the system's setpoint rather than at full nameplate (Article 750 and 220.70 in the 2023 edition, as adopted by your jurisdiction). See related: Alternatives to a Service Upgrade.
The exception is the customer who already has the car. Then the charger cannot wait. Install it on load management from the start, at a setting the later steps can live with, and write that setting into the plan so the next trade knows it exists.
Worked example: two orders, one house
A 1,700 square foot 1960s ranch. 100 amp service at 240 volts. Gas furnace and gas tank water heater sharing a masonry chimney, gas range, gas dryer, central AC. The owner wants to be off gas and plans to buy an EV next year. The values below are illustrative, chosen to show the mechanism; a real job uses its own measured numbers.
Order A, the order the phone rings in. The owner calls an electrician first for the EV charger. It goes in at 48 amps continuous, the charger's top setting. The next summer the AC fails; the HVAC contractor sizes a heat pump against the house as it stands and pairs it with 10 kilowatts of strip heat, about 42 amps. Then the water heater fails, and a plumber installs a 240-volt heat pump water heater on a 30 amp circuit. By the time the range comes up, the service cannot carry the heat strips, the charger and the water heater together, and the electrician quotes a service upgrade. The owner now believes electrification requires a new service, and in this order it did.
Order B, the sequence. A blower door test and an attic look come first. Air sealing and added attic insulation cut the design heat loss by roughly a fifth. The water heater is due, so it is replaced with a 120-volt plug-in unit on an existing circuit, after confirming the household's draw suits its recovery, and the furnace, now alone in the chimney, gets its venting check and a CO test on that visit. When the AC fails, the heat pump is sized to the smaller post-retrofit load, one nominal size smaller than Order A's, with 5 kilowatts of backup: 10,000 watts minus 5,000 watts is 5,000 watts, about 21 amps less than Order A on the coldest night. The furnace's removal triggers a venting check on what remains, and since the water heater is already electric, nothing gas is left on the chimney. Induction and the dryer follow. The charger goes in last, on load management, against a load study taken after the heat pump was running.
Whether Order B avoids the upgrade depends on the measurement at the end, and sometimes it does not. What it guarantees is that if an upgrade is needed, it is sized once, against known loads, instead of being discovered at step four.
ORDER B PLAN CARD - 1960s ranch, 100 A
STEP WHAT TRIGGER SERVICE
1 blower door, air seal, now none
attic insulation
2 120 V plug-in HPWH tank due existing ckt
furnace vent check, CO same visit
3 heat pump + 5 kW backup AC fails new 240 V ckt
furnace out, cap chimney same visit
4 induction range owner's choice measure first
5 HP dryer, cap old vent dryer fails 120 or 240 V
6 EV charger, load mgmt car arrives after load
study
7 gas meter removed last gas gone utility
What changes the order
- No air conditioning and a failing furnace. Space heating moves to the front because the house cannot wait. Do the envelope assessment on the same visit and size against what it finds.
- A house already tight. The blower door number says the envelope step has little left in it. Skip to step 2.
- The car is already in the driveway. Charger now, on load management, as above.
- A program requires an assessment or a specific order. Some incentive programs require an energy assessment before equipment. Program rules are the Rebates group's subject; check them before the first step, not after.
- Gas kept on purpose. A customer who wants to keep a gas range or fireplace changes what "last" means, and the fixed monthly gas charge stays. See related: Keeping Gas for One Appliance.
How to tell the sequence is being followed
On any visit to a house mid-conversion, three questions show whether a plan exists: Is there a written plan with the remaining steps? Was the last load added against a measured number or a guess? After the last gas appliance came out, did anyone check what was left on the vent? A house that answers no to all three is being converted by whoever called last, and the next trade through the door is the one who will find out.
References
- NFPA 70, National Electrical Code, Article 220 (220.55 range demand, 220.70 and Article 750 energy management, in the 2023 edition), as adopted by your jurisdiction
- See related: Electrical Panel Upgrades for Electrification Reference
- See related: Measuring Existing Load Before You Sell a Service Upgrade
- See related: What Removing a Gas Appliance Does to the Ones Left
- See related: Heat Pump Cold-Weather Operation Reference