How many kWh does it take to run a house during an outage?
The kilowatt-hours you need equal the power your chosen loads draw multiplied by the hours you want them to run. That is why sizing starts with a list of loads, not a guess about the whole house.
Two numbers matter. Kilowatts (kW) are how much power the house is drawing at a moment, and they decide how big the system has to be. Kilowatt-hours (kWh) are how much energy is stored, and they decide how long it lasts. A HUB20 handles 20 kW continuously on a 100 A service. A HUB40 handles 40 kW on a 200 A service. Both start with 28.8 kWh of storage.
A house running its network, lighting control, security and a few refrigerators draws a small, steady load. Add heat pumps, an induction range, a steam shower and an EV charger and the draw climbs fast, which shortens run time on the same battery. The design job is to match the system to the loads you care about.
Can I run my whole house on batteries?
You can, but it is usually not the best plan. RoseWater says this is the most common first question it hears, and it answers with another one: what problem are you solving?
- A one-second blink. Any always-online system handles it. The house never notices.
- A two-hour outage. A properly sized battery carries the important systems through it.
- A week without power once every twenty years. This is where a generator belongs, behind the battery system.
Battery-only backup sized for the third case is really a generator replacement, and it does nothing for power quality on the other 364 days. RoseWater’s Whole Home tier exists for owners who will not accept any repair or replacement, especially of built-in equipment, and it usually means multiple HUBs and a generator in one design.
What are critical or essential loads?
Critical loads are the systems whose failure would be a severe inconvenience or an expensive repair. RoseWater’s Power Plan worksheet groups a home into 21 categories and asks the owner to circle the ones that matter most.
| Tier | What it covers | Typical system |
|---|---|---|
| Essential Protection | Lifestyle-critical, microprocessor-heavy systems that should always be protected. For most homes, that means the network, home and lighting controls, security and computers | HUB20 |
| Enhanced Protection | Essential, plus microprocessor-heavy systems that are not lifestyle-critical. Owners often add kitchen appliances, entertainment and shade motors here | HUB40, ideally with a generator |
| Whole Home Protection | Everything in the home, for owners who find any repair or replacement unacceptable | Multiple HUBs, often with a generator, custom designed |
The 21 categories are home and lighting controls, entertainment, computers and servers, home healthcare, kitchen appliances, lighting fixtures, basic outlets, elevator, EV charging, HVAC motors, outdoor TV, networks, security, HVAC controls, shade motors, smart plumbing, wine and spirits room, motor loads, pool equipment, outdoor lighting and outdoor kitchen. Our Power Plan tool uses the same list.
A few items surprise people. Smart plumbing and steam systems have control boards that fail after hard shutdowns. A wine or cigar room is a collection that depends on stable refrigeration and humidity. Home healthcare equipment may be the single most important load in the house.
How long will a 28.8 kWh battery last?
A 28.8 kWh battery lasts as long as your load allows, so the honest answer is a range. RoseWater’s competitive analysis lists about 60 minutes at full rated draw on the standard battery, and run time stretches into hours as the load comes down.
That is why we never quote a run time before we see the loads. One RoseWater owner in Florida reported a nine-hour backup for refrigeration, low-voltage systems, AV and security. Another house with the same battery and a heavier list would see less. If the run time on your list falls short, there are three levers: add extended battery packs, move large motor loads to a generator, or trim the list.
Extended battery packs come in two sizes. A three-shelf pack adds 28.8 kWh and a five-shelf pack adds 40 kWh, for both the HUB20 and the HUB40.
Should HVAC and well pumps be on battery backup?
HVAC controls should be on battery, and large motors are usually better on a generator. The difference is the size of the load.
Thermostats, zone controllers and air handler boards are small electronic loads that hate interruptions, so they belong with the essential systems. Compressors, well pumps and pool pumps are motor loads. They draw much more power, and they can run for hours in a winter outage, which uses up battery capacity quickly. In a lot of New England homes, especially rural homes on a well, the plan is a battery system for the electronics and a generator behind it for heat and water in a long outage.
What RoseWater does differently
Sizing a RoseWater system covers more than run time, because a HUB does more than store energy. It is always online, so everything on it gets surge and lightning protection, voltage regulation and noise filtering every day, with no transfer time when the grid fails. The loads you put on the HUB are the loads you protect from power quality problems as well as outages.
That changes how we build the list. A theater processor might use little energy, but it is exactly the kind of equipment that dies from repeated sags. It goes on the HUB even if run time is not a concern.
How we size a system
Sizing starts with your Power Plan and ends with an engineered design. You pick the categories that matter in our Power Plan tool. We review it, visit the house, and gather the electrical single-line diagram, riser diagrams and panel schedules, which your electrician can usually provide. We register the project with RoseWater’s engineering team, size the HUB and batteries together, and coordinate the electrical tie-in with your licensed electrician. If you’d rather talk first, contact us.
