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 ObjectivesUnderstand HVAC system air leakage testingrequirements in the 2009 IECCRecognize the benefits of sealing ducts for savings,system performance and indoor air qualityUnderstand how ducts are tested for leakageIdentify resources for local building departmentsIdentify the best techniques to seal duct systems; whatinspectors should see on inspectionsUnderstand the IECC requirements for sizing of HVACequipment
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 Mandatory RequirementsAll ducts, air handlers, filter boxes and buildingcavities used as ducts shall be sealed (Section403.2.2)Duct tightness shall be verified by testing Only Exception: Duct tightness test is notrequired if the air handler and all ducts arelocated within conditioned space
SEAL DUCTS,SAVE ENERGYSealing ducts is a cost-effectiveenergy efficiency practice that givesa 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 Mandatory RequirementsPost construction testsOption 1 Leakage to outdoors: ≤8 cfm/per 100 ft2 of conditioned floor area OROption 2 Total leakage: ≤12 cfm/per 100 ft2 of conditioned floor area
Duct Tightness Tests Mandatory Requirements 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 Mandatory Requirements 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
Mastic Sealant Non-toxic – Low VOC Green 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 SYSTEMBoots and Cans Seal seams with mastic Thin mastic will crack Make seal permanent Plug Don’t Paint Thick as a Nickel = .077 in 1/16 inch = .0625 in
FLEX DUCT TO METAL Flexible DuctsSeal 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 Vapor barrier should be complete. barrier) All holes, rips, and seams must be sealed with mastic or approved tape
AIRTIGHT DUCT SYSTEMMetal 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.
AIRTIGHT HVAC SYSTEMAir 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.
AIRTIGHT DUCT SYSTEMAll Duct TypesRegister boxes should be sealed to the drywall or floor with caulking or mastic
AIRTIGHT DUCT SYSTEMAll Duct TypesRegister 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 thermalboundary 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 inconditioned 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
For Sealing Existing Systems Tools & Materials Head lamp, hat with light, or flashlight A work board to span joists in attics Gallon pail and 2-3 caulk tubes of mastic Caulk Gun, mastic brush, fin and plenum brush Roll of mesh 2-3 pairs of latex gloves 2-3 cloths, can of coil and fin cleaner to wipe jointsclean before applying mastic and clean up Utility knife and telescoping mirror Pliers, screw driver and tin snips
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 ductto connectionRoll back insulation andouter coverSeal inner core withmastic and bandRoll insulation downand vapor barrier/outercoverPut band and seal withmastic
Wrap Ducts with insulationInsulation may be installed over wet masticbut do not move the ducts too much or masticseal could be damaged.All duct support work should be done beforeapplying masticWait 2 -4 hours and water based mastic willbe dry to the touch
OversizingWhat 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 Mandatory Requirements 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 SYSTEMLoads 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 Vision2012 IECC 30% More Stringent 2006 IECCMore 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