Sizing on Fondsites

Watts, kWh, and Loads: The Home Energy Math That Matters

Mon, 04 May 2026 00:00:00 +0000

Most home energy confusion comes from mixing up watts and kilowatt-hours.

Watts are the speed of energy use. Kilowatt-hours are the amount of energy used over time. A 100-watt device running for 10 hours uses 1,000 watt-hours, or 1 kWh.

The formula

Use this:

watts x hours = watt-hours

Then divide by 1,000:

watt-hours / 1,000 = kWh

A 60-watt router and network setup running for 24 hours uses 1,440 Wh, or 1.44 kWh. A 1,500-watt appliance running for 20 minutes uses about 0.5 kWh. Short high-power loads and long low-power loads both matter.

Backup Power Sizing: Build the Smallest System That Solves the Outage

Mon, 04 May 2026 00:00:00 +0000

Backup power sizing is not about buying the largest device you can tolerate. It is about matching power to the outage you are actually planning for.

Start with Outage Priority List . Then size around the loads that made the cut.

Step 1: List the loads

For each load, write:

watts
hours needed
whether it has startup surge
whether it is safety-critical
whether it can be cycled or delayed

Use measured data where possible. A refrigerator is easier to plan when you know its daily kWh and surge behavior.

Inverter Sizing: Continuous Watts, Surge, 120V, 240V, and Load Reality

Mon, 04 May 2026 00:00:00 +0000

An inverter converts battery DC power into AC power your home loads can use. Sizing it badly creates a frustrating system: plenty of energy stored, but not enough power to run the loads you care about.

The two ratings

Continuous output

This is what the inverter can provide steadily. Add up the loads that may run at the same time.

Surge output

This is the short burst needed by motors, pumps, compressors, and some tools. A refrigerator, freezer, sump pump, or air conditioner may need more startup power than its running watts suggest.

Heat Pump Sizing Basics: Why Bigger Is Not Automatically Better

Mon, 04 May 2026 00:00:00 +0000

Heat pump sizing is a comfort decision, not a bragging contest.

Oversized equipment can short-cycle, miss humidity targets, create uneven comfort, and wear poorly. Undersized equipment can struggle during design conditions. The right answer comes from the home, not a rule-of-thumb guess.

What affects sizing

climate and design temperatures
insulation and air sealing
window area and shading
duct condition
ceiling height
room layout
internal loads
ventilation and humidity
backup heat strategy

This is why a proper load calculation matters.