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Get to Know LEED®: Efficient Heating and Air Conditioning Equipment is not Enough! Get the Ducts Done Right.

If you’re considering new heating or air conditioning equipment to improve your home’s
energy efficiency and thermal comfort, you’re taking a step in the right direction. But
unless you get the heating and cooling distribution - meaning the ducts through
which your cool and/or warm air travels - done right, you’re leaving money on the table,
so to speak.

The LEED® for Homes green building program awards a project up to three points for
measures aimed at optimizing the distribution of heating and cooling. And there’s a good
reason to do so. According to the LEED for Homes Reference Guide,

“In typical new homes, duct leakage may account for 15% to 25% of total
heating and cooling energy use. Leaky supply ducts running through
unconditioned spaces may dump conditioned air outside or draw
unconditioned outside air into the home…Reducing the duct leakage rate
saves energy, but more importantly, properly designed and sealed duct
systems deliver air more effectively within the home. Unevenly hot or
cold rooms are often caused by leaky ducts.”

So what is Sunset Green Home doing to ensure occupant comfort and earn points toward
LEED certification? We’re following the LEED for Homes green building program’s
guidelines for duct design and installation.

First, Sunset Green Home is minimizing the number and size of duct runs by installing
Mitsubishi Electric’s Multi-Zone Hyper Heat mini split system for heating and cooling. The
system has a single outside air source heat pump (compressor) connected to five air
handlers, each of which is attached to short duct runs that serve the rooms in the
house. By contrast, duct work for a conventional forced air system might have large
ducts running throughout the home from a single heat or cool air source – making
efficiency losses from the duct work more likely.

Air handler in the background with short duct runs to serve the bedrooms below.

Air handler in the background with short duct runs to serve the bedrooms below.

Second, Sunset Green Home has used industry-approved software to calculate the amount
of air required for each room based on such factors as the size of the room, the number
and size of its windows, and which direction it faces. The ducts have been designed
(sized) to deliver exactly what each room needs based on its unique conditions.

Short duct run sized for required air flow.

Short duct run sized for required air flow.

Third, Flanders Heating & Air Conditioning, Sunset Green Home’s HVAC contractor, has
followed the LEED for Homes program’s guidelines for locating the air handlers and
short ducts runs that will serve each room. Air handlers have been placed inside the
conditioned envelope of the house. Three air handlers are in the attic of the house (which
is insulated at the rafters, and therefore part of the home’s conditioned envelope) and two
are located in closets on the first floor of the home.

Air handler and ducts located in the conditioned attic space.

Air handler and ducts located in the conditioned attic space.

Lastly, Flanders has followed the LEED for Home’s guidelines for duct sealing and
insulation.

  • Sheet metal ducts will have their joints and seams sealed
  • Insulation seams will be sealed with foil tape or duct butter
  • Sheet metal supply ducts will be wrapped with R-6 foil faced fiberglass insulation
  • When installation is complete, all ducts will be sealed to prevent construction dust and debris from entering
Air handler with insulated ducts.

Air handler with insulated ducts.

Flanders is also installing acoustical lining in all sheet metal return ducts. While not
critical to the system's energy efficiency, acoustical lining contributes to occupant
comfort by ensuring that the system operates quietly.

Getting the ductwork right can contribute to a high performing heating and cooling
system. If you're considering installing a new system or upgrading your existing HVAC
system, be sure to discuss the distribution system with your contractor. Limit air leakage
to outside of the conditioned envelope of your home by optimally sealing, insulating and
locating your ductwork.

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