HVAC Isn't Just Square Footage

You'll sometimes hear rules of thumb such as 500 or 600 square feet per ton of air conditioning.

Those can be useful for rough conversations, but they aren't how a properly designed HVAC system should ultimately be sized.

A professional load calculation considers insulation, windows, orientation, air leakage, ceiling heights, climate and other characteristics of the actual house.

That's especially important in a custom home.

One System With Dampers vs. Multiple Systems

One way of controlling different areas of a house is a zoned system using dampers.

Motorized dampers direct conditioned air toward different zones depending on which thermostat is calling for heating or cooling.

There are applications where that works well.

I actually have zoning downstairs in my own home. My first floor is large enough that separating the bedroom area from the main living area gives us additional comfort at night.

But there's an important distinction: those spaces are still within essentially the same first-floor environment.

Upstairs and downstairs can behave very differently.

That's why, depending on the house, separate equipment serving different floors can sometimes provide better control than asking one system to satisfy two very different environments.

Lowest Initial Price Isn't Always the Best HVAC Design

This becomes particularly important when builders are competing for a project.

HVAC equipment is expensive. Reducing the amount of equipment can make a construction proposal look more attractive.

But I don't think the conversation should stop at:

“What's the least amount of equipment we can install?”

The better question is:

“What system is going to make this particular house comfortable?”

Those aren't always the same answer.

A homeowner may live with the HVAC decisions we make during construction for the next 15 or 20 years.

Saving money initially isn't much consolation if you're lying in bed every summer wondering why the upstairs won't cool properly.

In custom construction, comfort should be designed into the house—not addressed after the homeowner moves in.