Generator for Central AC: Tonnage and Wattage Guide

The central AC question in Texas

In a Texas summer, a central air conditioner is often the largest appliance a backup power unit would be asked to run, and in a Texas winter the same home might be asking about heating instead. The shopping question is which appliances you plan to power, and that mix changes with the season.

A central AC unit carries its own label with two terms a generator shopper will encounter: tonnage and SEER. Tonnage describes the cooling capacity of the air conditioner. SEER describes how efficiently it turns electricity into cooling. Neither number is printed on a generator listing; generator listings use watts. Understanding how the two sets of words relate is the first step before you choose between a portable and a standby unit.

Tonnage and SEER as listing terms

Tonnage is a measure of cooling capacity. A higher tonnage means the unit can remove heat from a larger space, and a lower tonnage means less. SEER, short for seasonal energy efficiency ratio, compares the cooling output a unit produces with the electricity it draws. A unit with a higher SEER delivers more cooling per watt, which is why efficiency is part of the backup power conversation.

Neither tonnage nor SEER is converted into watts on this site. The figures belong on the AC unit's nameplate and in its manual, and you can write them down before you talk to a generator maker or a licensed electrician. The AC maker's page is the place that states how much power the unit draws under starting and running conditions.

Reading watts on a generator listing

Generator listings typically show two watt figures. Starting watts is the higher figure, and running watts is the steady figure the unit supplies while it runs. Many listing titles place the starting figure first, because a central AC's compressor motor draws a brief surge of power when it starts. The difference between the two figures is explained in a separate article.

A listing may state a single watt figure, and that figure is often the starting one. To read the running watts, open the maker's page for the generator model. Some listings also carry words such as electric start, dual fuel, RV ready, and a carbon monoxide sensor and shutoff. For the carbon monoxide sensor and shutoff words, follow the maker's manual and read the CPSC and CDC carbon monoxide pages in the sources below.

Who decides whether a unit fits your AC

How many watts a central AC needs depends on the tonnage, the SEER, the age of the unit, the voltage in your area and how the compressor cycles. No listing on this site states a number that answers whether a given unit will run your central AC, and no listing here should be read as one. The generator maker and a licensed electrician are the people who answer that question.

If the goal is a whole house, the connection between the generator and the home's wiring is also their question. A licensed electrician, the generator maker and the local permit office decide how a unit connects to a home. The word "transfer switch" appears on standby listings as a term for that connection. The whole-house guide shows the types of listings to compare.

Shopping for a Texas home

Before summer, the backup question is air conditioning. A home that wants its central AC running through a summer outage is usually looking at an installed standby unit, because a standby unit is sized and connected by an installer. A portable unit is a separate tier and serves a smaller set of loads. The summer guide lists portable and inverter models, and the whole-house guide lists standby models.

A rural home on a well adds a well pump to the same shopping question, and the combined load belongs on the maker's page and with an electrician. The rural guide is the place to start for that situation.

If the plan is essentials only and the central AC waits for the grid, a mid-size portable unit may be the right tier. The essentials guide compares those listings. Fuel is a separate question: a home on a propane tank may prefer a dual-fuel listing, and the dual-fuel guide and the propane versus gasoline article explain the listing words.

Preparing before the season

Texas prepares for both cold and heat, and the Texas Division of Emergency Management, Texas Ready, and the National Weather Service cold and heat safety pages list what a household should plan and stock before winter storms and summer heat. Those pages are the public starting point for deciding what backup power should cover.

A pre-season checklist for the generator itself, as the maker's manual describes it, includes reading the hour meter, checking oil as the manual specifies and following the maker's storage instructions between seasons. The maintenance article covers that checklist in general terms.

What to pick for your situation

Questions

What does tonnage mean on a central air conditioner?

Tonnage is the cooling capacity of the unit. A higher number means the unit can remove heat from a larger space, and a lower number means less. The exact tonnage is on the AC unit's nameplate and in its manual.

What does SEER stand for?

SEER is the seasonal energy efficiency ratio. It compares the cooling a unit produces with the electricity it draws. A higher number means more cooling per watt, which makes efficiency part of the backup power conversation.

Which watts figure matters for a central AC?

Both starting and running watts matter. Starting watts covers the brief surge when the compressor starts, and running watts is the steady figure. The generator maker's page states both; a listing may show only the starting figure.

Can this site tell me what size generator runs my central AC?

No. This site explains listing terms and does not size a home. The generator maker and a licensed electrician answer whether a unit matches your AC, based on the AC's tonnage, SEER and the unit's stated watts.

Do I need a standby generator to run central AC?

A standby unit is the whole-house tier and is connected by a licensed electrician. A portable unit is a different tier and serves a smaller set of loads. Read the whole-house guide and the portable guides to compare the two shopping paths.

Where do I find the tonnage and SEER of my AC?

On the air conditioner's own nameplate and in its manual. Write the figures down before you talk to a generator maker or a licensed electrician.