Everyone wants their new home to be comfortable, healthy and energy-efficient. Professional builders satisfy these expectations with high insulation levels, careful air sealing and optimized heating and cooling systems. In fact, few homeowners realize that with today's construction methods, their health and comfort depend more than ever on the mechanical equipment. For this issue, the focus is on forced air systems. In an upcoming edition, radiant systems will be explored and compared.
The most important pieces of equipment are the furnace and air conditioner. Unlike on a tropical island, where mild temperatures allow windows to be open much of the year, physical comfort in our mountain environment depends on having a furnace and air conditioner of the right size.
In the past, mechanical contractors used rule-of-thumb guidelines to match the equipment to the house. A lot of contractors still do this. For example, a guideline might be 30 BTUs of heating capacity per square foot of living space, or one ton of cooling per 500 square feet. The rule wasn't very precise, but a drafty old home would lose much of the conditioned air to the outside anyway, so imprecision was no big deal.
Today's efficient new homes leak less air and thus need less heating or cooling capacity, so rule-of-thumb sizing will likely give you a bigger furnace or air conditioner than you need.
But isn't bigger better? Not in this case--in fact, it's just the opposite.
An oversized furnace can actually make an efficient home less comfortable by excessively heating some rooms before the warmed air can reach the thermostat. An oversized air conditioner can cool things down so fast that it shuts off before the equipment has time to dry the air to a comfortable level, leaving the house feeling cold and clammy. No one will be happy, except perhaps the mold and mildew growing in the bathroom or behind the refrigerator, or the dust mites and other allergens that breed faster at higher humidity. That's bad news for anyone who breathes.
Good mechanical contractors eliminate these problems by using only the most accurate sizing protocols. The most common of these, Manual J from the Air Conditioning Contractors of America, figures the exact amount of heating and cooling needed by considering all of the home's features: air leakage rates, insulation levels, the type and square-footage of roofing and siding, the model and orientation of each window, the dimensions of soffit overhangs, and other data.
In the past, these measurements and calculations took a lot of time, but today's mechanical contractors have the advantage of sophisticated software. Such programs eliminate much of the work by, for instance, automatically calculating the solar gain and average seasonal temperatures using data from Google maps, the local building code, and other online databases. The builder and mechanical contractor can then revise the numbers and make any adjustments needed to account for the home's unique features.
These software programs also help the contractor size the home's ductwork and choose registers that distribute just the right amount of air to each room without noise or drafts.
Accurate sizing is one reason that professional builders work only with top-notch mechanical contractors. In fact, the mechanical contractor is a crucial team member--a trusted advisor who understands that energy-efficient construction is an opportunity to use measured data to optimize comfort and health.
Brink Custom Homes
P.O. Box 1902
Tahoe City, CA 96145
(530) 583-2005 – phone
(530) 583-4405 – fax