HVAC Install - Trust But Verify

Quality HVAC System Installation

Trust But Verify

Quality HVAC System Installation

The goal for a Heating, Ventilation and Air Conditioning (HVAC) system is to provide proper air

flow, heating, and cooling to each room

Instructor

Barbara Collins

ERH West

Building Performance Consultant Certified NAHB Green Building Verifier Certified RESNET HERS Rater Energy Star Homes Partner Certified Environments for Living Verifier

Class Objectives

Understand HVAC system air leakage testing requirements in the 2009 IECC

Recognize the benefits of sealing ducts for savings, system performance and indoor air quality

Understand how ducts are tested for leakage Identify resources for local building departments Identify the best techniques to seal duct systems; what

inspectors should see on inspections Understand the IECC requirements for sizing of HVAC

equipment

Current Code Requirements

Must comply with all aspects of UL181 standards

Fittings, joints & seams of duct system shall be made substantially air tight by means of tapes, mastics, gasketing or other means.

Ducts - IECC

Insulation (Prescriptive) Ducts outside the building

envelope: R-8

All other ducts: R-6

Sealing (Mandatory) Joints and seams shall comply with IRC,

Section M1601.4.1

Building framing cavities shall not be used as supply ducts

2009 IECC Duct Tightness Tests

All ducts, air handlers, filter boxes and building cavities used as ducts shall be sealed (Section 403.2.2)

Duct tightness shall be verified by testing

Only Exception: Duct tightness test is not required if the air handler and all ducts are located within conditioned space

Mandatory Requirements

SEAL DUCTS,

SAVE ENERGYSealing ducts is a cost-effective

energy efficiency practice that gives a high return on investment

HVAC System

Poor design and installation increases energy costs 10 –30%

Sizing Design Installation

Home Energy Use

Residential energy use 22% of U.S. total 25% of carbon emissions in U.S. Heating & cooling is 40 – 60 % of home

energy use

Why seal ducts

Leaks waste energy and money Average system leakage

New construction 20% Existing homes 30%

Duct sealing reduces heating and cooling energy losses and saves money

Other Problems

Duct leakage reduces air flow, conditioned air isn’t delivered to rooms which can cause wide temperature swings between rooms

IAQ issues with return leaks drawing in air from attics, garages, crawlspaces

Pressure differentials can cause excess building air leakage and back drafting

Duct Tightness Tests

Post construction tests Option 1

Leakage to outdoors: ≤8 cfm/per 100 ft2 of conditioned floor area

OR Option 2

Total leakage: ≤12 cfm/per 100 ft2 of conditioned floor area


Duct Tightness Tests

Rough-in test Options Option 1

Total leakage ≤6 cfm/per 100 ft2 of conditioned floor area

OR Option 2

If air handler not installed at time of test total air leakage ≤4 cfm/per 100 ft2


Exceptions: Duct tightness test is not required if the air handler and all ducts are located within conditioned space

Thermal Boundary is also used to define whether testing is required.

Insulation installed on underside of roof sheathing, AHU and ducts in attic, can be considered within thermal boundary

Ventilation

Outdoor air intakes and exhausts shall have automatic or gravity dampers that close when the ventilation system is not operating


Test Protocol

Pressurize the HVAC system, measure CFM of air required to reach pressure

Test at a pressure differential of 0.1 in w.g. (25Pa) across entire system, including manufacturer’s air handler enclosure

Test Equipment

Testing at rough-in

Testing Post Construction

Testing leakage to outside

Mastic Sealant

Non-toxic – Low VOCGreen credits

Recommended Set time = 20 hours

More on Mastic

High strength adhesive compound Usually applied by trowel, brush, caulking gun

or hand 3 types- water-based; solvent-based; and

two-component curing systems Water-based is the safest and easiest to use

It performs as well and in some cases better than the other 2

VOCs in mastics

Volatile organic compounds In water-based mastics, the only volatile

compound is water which is inorganic VOCs are infinitesimally small (not

recordable) Water-based mastics pose a low health risk

compared to solvent-based and two-component mastics

Safer for the user, better IAQ, greener

How to apply mastic

Step 1 - Clean Duct Surface Wipe dust oil and grease from the duct surface

Step 2 - Apply the mastic

Gaps less than 1/4″, load brush with mastic and coat entire joint with a continuous strip

Use brush end to work mastic into joint Spread mastic at least one inch on each side

of the joint. The mastic should be thick enough to hide the

metal surface of the duct.

Mesh for Gaps

If gap is larger than 1/4 inch use fiberglass mesh too

If mesh is sticky on one side, cut enough to cover joint, press in place, then completely cover it with mastic.

If mesh does not have a sticky side, apply a thin layer of mastic, press mesh into the mastic, then apply a finish layer of mastic.

AIRTIGHT DUCT SYSTEM

Boots and Cans Seal seams with

mastic

Thin mastic will crackMake seal permanent Plug Don’t PaintThick as a Nickel = .077 in1/16 inch = .0625 in

FLEX DUCT TO METAL

Flexible Ducts Seal inner sleeve & outer

sleeve

Plastic strap holds the inner liner firmly to the duct or fitting.

Mastic seals liner to connection and covers the end of the liner

Use draw band to hold outer sleeve (vapor barrier)

Vapor barrier should be complete. All holes, rips, and seams must be sealed with mastic or approved tape


Metal Ducts and Plenums, Duct Board Boxes

Openings greater than 1/4 inch should be sealed with mastic and mesh

Openings less than 1/4 inch should be sealed with mastic

Special attention to collar connections to duct-board and/or sheet metal; seal around the connection with mastic

Ts Ys & Ls

Use mesh tape to strengthen the joint where ducts of different shapes meet.

Seal all seams, even manufactured ones.

Seal Gores

Sealant applied, still leaks

FABRICATION & INSTALLATION GUIDELINES

The air handler box should be air-tight

AHUs & Plenums

Fill all openings for wiring, plumbing and refrigerant lines.

Seal all seams in the air handler and plenums.

Tape around access panels, so they can be opened for service.

Air Handler Leaks

Mechanical Systems & Equipment

AIRTIGHT HVAC SYSTEM

Air handlers on platforms May be located in a closet indoors Framers must be told not to put plywood top

on before walls are sheetrocked (or duct board) to underside of platform floor

All wall surfaces must be sheetrocked next to and in platform

Seal all joints

Boots

Seal all joints, including manufactured seams.

The transition between the duct and boot may require mesh tape.


All Duct Types

Register boxes should be sealed to the drywall or floor with caulking or mastic

SHEET METAL CONNECTIONS

Start the inner fitting into the outer fitting Apply a 2” wide band of mastic to the exposed part of

the inner fitting Fully seat the joint and mechanically fasten with

sheet metal screws or rivets Apply a 2.5” wide band of mastic to the outside of the

joint covering the screws or rivets and joint gap Allow at least 12 hours drying time before starting

system Temperature and humidity conditions can vary,

longer dry times may be required

Locating ducts within thermal boundary Within thermal boundary means within

insulated space and within the air barrier boundary.

Attics and crawlspaces can be but are usually not conditioned space

Critical that space is truly indoors and sealed from unconditioned areas

Multi-level dwellings more easily accommodate ducts in conditioned space

Ducts in Unconditioned Space

Usually ducts are located in attics and crawlspaces

Big temperature differences increase conduction losses and loads Long duct runs in attics lose 15%+ of cooling

capacity before end Convection losses by leakage

Benefits of locating ducts in conditioned space Ducts can be smaller May have shorter runs reduce pressure drop

and improve efficiency Can reduce HVAC system costs by reducing

loads Improve comfort No Testing in 09 IECC

EXISTING HOMES

In existing homes, not unusual to find disconnected duct components, takeoffs loose from ducts or ducts disconnected from register boots

Tools & MaterialsHead lamp, hat with light, or flashlightA work board to span joists in attics Gallon pail and 2-3 caulk tubes of masticCaulk Gun, mastic brush, fin and plenum brushRoll of mesh2-3 pairs of latex gloves 2-3 cloths, can of coil and fin cleaner to wipe joints clean before applying mastic and clean upUtility knife and telescoping mirrorPliers, screw driver and tin snips

For Sealing Existing Systems

Sealing Priorities

1. Disconnected components

2. Connections between the air handling unit and the plenums

3. All seams in the air handling units and plenums, takeoffs, boots, and other connections, especially site-built items.

EXISTING HOMES

Leaks connected to the outdoors are more important than leaks inside home’s thermal envelope

Holes near the air handler are more important than distant holes with relatively low pressures

Supply system leaks waste more energy than return system leaks

Furnaces

Remove tie holding duct to connection

Roll back insulation and outer cover

Seal inner core with mastic and band

Roll insulation down and vapor barrier/outer cover

Put band and seal with mastic

Wrap Ducts with insulation Insulation may be installed over wet mastic

but do not move the ducts too much or mastic seal could be damaged.

All duct support work should be done before applying mastic

Wait 2 -4 hours and water based mastic will be dry to the touch

Oversizing

What do you get when you combine cognitive bias with inaccurate information?

Oversizing

Old Rules of Thumb One Size Fits All

US Department of Energy Most systems are oversized, increasing

installation cost for every house

Oversizing

Sizing example

2000 SF House with standard metal windows w/ .75 U-Value and .88 SHGC and 20% duct leakage

Calculated Sensible cooling load = 58880 Btu

Equipment Sizing

Load calculations determine the proper capacity (size) of equipment

Goal is big enough to ensure comfort but no bigger

Calculations with ACCA Manual J protocol or other approved methods


Oversizing

Sizing example Same 2000 SF house with Low-E windows

and tight duct system @ 5% leakage Sensible cooling load = 43877 Btu Average of 1-2” decrease in duct diameter

sizes

Oversizing

Installation cost is higher Operating cost over life of equipment is

higher Can cause comfort problems Improvements in building envelope reduce

loads

Right Sizing

Costs less to install – saves builder money Costs less to operate - not starting and

stopping all the time Short cycling can cause bigger swings in

supply air, less comfort Better humidity control

DESIGN HVAC SYSTEM

Loads and CFM Calculation ACCA Manual J Load Calculation or

equivalent required Calculate heat loss and heat gain for each

room

Total room loads to determine system requirements.

Manual J –Load Calc

The local climate – ASHRAE 30 year average Size, shape, and orientation of the house Insulation levels Window area, location, and type Air infiltration rates Number of occupants Types and efficiencies of lights and major home

appliances (which give off heat)

ACCA - Air Conditioning Contractors of America www.acca.org

“It’s tough to make predictions, especially about the future.”

- Yogi Berra

U.S. Dept of Energy

30/30 Vision

2012 IECC 30% More Stringent 2006 IECC

More verification testing

A Quality HVAC System

Be properly sized to provide correct air flow, and meet room-by-room calculated heating and cooling loads.

Have sealed ductwork that will provide proper air flow.

Be installed with a return system designed to provide correct return air flow.

Have balanced air flows between supply and return systems to maintain neutral pressure in the home.

Be properly charged with refrigerant

Verifying Charge

Ductwork

Single most important energy measure for most homes- low hanging fruit

Locating inside conditioned space is optimal

Seal joints with mastic not duct tape

Equipment Size

Oversizing is common and expensive – upfront and during life

Sizing properly can reduce cost and help pay for increased cost of other efficiency features

Learn from the mistakes of others. You can't possibly live long enough to make them all yourself

--Sam Levinson

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HVAC Install - Trust But Verify

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