What size furnace do I need?

A quick estimate by area and climate zone. A Manual J load calculation is best before buying.

House length (ft)House width (ft)Climate zoneFurnace efficiency

Furnace input size

78,000 BTU

Heat the house needs74,000 BTU

Area2,000 sq ft

How to measure

Measure the house's length and width, and pick your climate zone.

Tips from the field

Houston and most of the Gulf Coast are in climate zone 2.
Furnaces are sold by input BTU. Efficiency tells you how much of that reaches the house.

What you'll need

Gas furnaceFurnace filtersSmart thermostat

Common questions

What climate zone is Houston?

Zone 2, a hot and humid climate.

What does 95% efficiency mean?

95% of the fuel's heat reaches the house, and 5% goes out the flue.

What is a Manual J?

A full load calculation a contractor uses to size heating and cooling accurately.

Add this calculator to your websiteFree

Contractors, bloggers, and real estate agents can put this calculator on their own site for free. Copy the code below and paste it into any page.

<iframe id="hc-furnace-size-calculator" src="https://housecalcs.com/embed/furnace-size-calculator" title="Furnace size calculator" width="100%" height="640" style="border:0;max-width:640px" loading="lazy"></iframe>
<p style="font:14px sans-serif">Free <a href="https://housecalcs.com/tools/furnace-size-calculator">furnace size calculator</a> from HouseCalcs</p>
<script>window.addEventListener("message",function(e){if(e.origin==="https://housecalcs.com"&&e.data&&e.data.hcSlug==="furnace-size-calculator"){var f=document.getElementById("hc-furnace-size-calculator");if(f)f.style.height=e.data.hcHeight+"px"}});</script>

More for heating, cooling, and water

AC size calculator

What size air conditioner do I need?

Room air flow (CFM) calculator

How big an exhaust fan do I need?

Water heater size calculator

What size water heater do I need?

Printed from housecalcs.com/tools/furnace-size-calculator