high efficiency gas furnaces - carsondunlop.com
TRANSCRIPT
Copyright 2019 Carson, Dunlop & Associates Ltd.
HIGH EFFICIENCY
GAS FURNACES
Alan Carson
CARSON DUNLOP
March, 2019
Copyright 2019 Carson, Dunlop & Associates Ltd.
Before we start
–Want to make sure we are all
on the same page……
Copyright 2019 Carson, Dunlop & Associates Ltd.
Definition of a Home Inspection
A business with illogically high liability, slim profit
margins and limited economies of scale. An
incredibly diverse, multi-disciplined consulting
service, delivered under difficult in-field
circumstances, before a highly stressed, hostile
audience with differing interests, in an impossibly
short time frame, requiring the production of an
extraordinarily detailed technical report almost
instantly, without benefit of research facilities or
resources.
Copyright 2019 Carson, Dunlop & Associates Ltd.
GOALS
–Rules of the game
–Identify high efficiency gas
furnaces
–Understand how they work
–Understand how they fail
(Focus on upflow furnaces)
Copyright 2019 Carson, Dunlop & Associates Ltd.
OAHI STANDARD - HEATING
Inspect:
• Installed heating equipment.
• Vent systems, flues and chimneys.
• Fuel storage systems
• Distribution systems.
Copyright 2019 Carson, Dunlop & Associates Ltd.
OAHI STANDARD - HEATING
Describe:
• Energy source – natural gas
• Heating method – furnace
• Chimney or venting material – plastic
• Combustion air source – outside/basement
• Exhaust venting method – induced draft
/direct vent
Copyright 2019 Carson, Dunlop & Associates Ltd.
WE DESCRIBE
• Fuel
• Size
• Age
• Efficiency
From data plate and
Technical Reference Guide
Copyright 2019 Carson, Dunlop & Associates Ltd.
WHAT WE REPORT
• Significantly deficient or near end of
life
• Why it’s so & why it matters
• TELL THEM WHAT TO DO!!!!!
– correct or monitor
• Anything we didn’t inspect and why
Copyright 2019 Carson, Dunlop & Associates Ltd.
NEAR END OF LIFE
Need to know -
1. Life expectancy (e.g. 15 to 20 years)
2. Age?
1. Carson Dunlop’s Technical Reference
Guide
2. Manufacturer
Copyright 2019 Carson, Dunlop & Associates Ltd.
IDENTIFICATION
•How do we tell if
it’s a high
efficiency furnace?
•Just look!
Copyright 2019 Carson, Dunlop & Associates Ltd.
3.5 WAYS TO IDENTIFY
HIGH EFFICIENCY
1. Efficiency rating
• 90% + AFUE – What do letters mean?
• Check data plate - (Output/Input)
• Conventional – 80% SS: 60% Seasonal
• Mid – 80% SS: 80% Seasonal
• High – 90%+ SS: 90%+ Seasonal
Copyright 2019 Carson, Dunlop & Associates Ltd.
IDENTIFYING HIGH
EFFICIENCY FURNACES
2. “Condensing furnace”
• Exhaust gases cool and condense
• Condensate drain line
Copyright 2019 Carson, Dunlop & Associates Ltd.
IDENTIFYING HIGH
EFFICIENCY FURNACES
3. PVC/ABS vents (150°F/180°F)
– 100 to 150°F exhaust
• S636 PVC or CPVC (200°F)
– orange labels
– Since 2007
• PP (Polypropylene) – the new kid!
(230°F)
Copyright 2019 Carson, Dunlop & Associates Ltd.
IDENTIFYING HIGH
EFFICIENCY FURNACES
3.5. Sealed Combustion/Direct vent
• Use outside air
• Three advantages!
1. No depressurization/back-drafting
2. No waste of warm house air
3. No pollutants into furnace – gas, paint
remover, bleach, cleaning products, water
softener salts, etc.
Copyright 2019 Carson, Dunlop & Associates Ltd.
IDENTIFYING HIGH
EFFICIENCY FURNACES
Why 3.5?
• Direct vent - means high
efficiency
BUT….
• High efficiency - does not
necessarily mean direct vent
Copyright 2019 Carson, Dunlop & Associates Ltd.
IDENTIFYING HIGH
EFFICIENCY FURNACES
SUMMARY
1. 90%+ AFUE rating (data plate or model)
2. Condensate collection
3. PVC/ABS/S636/PP venting (low temp
plastic)
4. Sealed combustion (direct vent) – optional
Copyright 2019 Carson, Dunlop & Associates Ltd.
GETTING HIGHLY
EFFICIENT
So, how do we do it?
• Extract more heat from
combustion products
• How?
Copyright 2019 Carson, Dunlop & Associates Ltd.
GETTING HIGHLY
EFFICIENT
• Keep exhaust products in house
longer
• Expose to more house air
• More heat transfer
Longer heat exchanger surface
Multiple heat exchangers
Copyright 2019 Carson, Dunlop & Associates Ltd.
GETTING HIGHLY
EFFICIENT
• But there’s more to it…..
• Magic in condensation
• LATENT HEAT OF
VAPORIZATION
Copyright 2019 Carson, Dunlop & Associates Ltd.
GETTING HIGHLY
EFFICIENT
• Main products of combustion of
natural gas?
– Water
– Carbon dioxide
• The water (steam) is the key
Copyright 2019 Carson, Dunlop & Associates Ltd.
LATENT HEAT OF
VAPORIZATION
• Define BTU!
• Heating 1 lb. of water
• From 32°F to 212°F
– takes 180 BTUs
• From 212°F water to 212°F steam
– takes 970 BTUs!
• Condensing steam releases 970 BTUs!
Copyright 2019 Carson, Dunlop & Associates Ltd.
GETTING HIGHLY
EFFICIENT
•So, if we can get the
combustion gases to
condense……
Copyright 2019 Carson, Dunlop & Associates Ltd.
TWO ADVANTAGES
OF CONDENSING
We can get way more heat!
Plus –
Exhaust is so cool, we don’t need
chimneys!
Copyright 2019 Carson, Dunlop & Associates Ltd.
DISADVANTAGES
OF CONDENSING
But…….
Condensate rusts metal
–E.g. heat exchangers
Can we control the water?
Copyright 2019 Carson, Dunlop & Associates Ltd.
How much water does a
typical furnace produce
in a month?
Prize!
Copyright 2019 Carson, Dunlop & Associates Ltd.
a. 10 gallons
b. 25 gallons
c. 50 gallons
d. 100 gallons
e. 200 gallons
Copyright 2019 Carson, Dunlop & Associates Ltd.
CONDENSATE IS CORROSIVE
Need special heat exchangers
• Stainless steel
• Plastic coated steel
• Just the secondary HE – Why?
Copyright 2019 Carson, Dunlop & Associates Ltd.
GETTING HIGHLY
EFFICIENT
• So, we can condense the combustion
gases
• And capture way more heat
• If we collect the water properly
• And we don’t rust the heat exchanger
Copyright 2019 Carson, Dunlop & Associates Ltd.
SEQUENCE OF OPERATION
1. Thermostat call
2. 25-second purge
3. Draft checked
4. HSI warms up
(15/20 sec.)
5. Gas valve opens
6. Prove flame
(2/8 sec.)
7. Blower on 30-60 sec.
8. Firing rate & blower
rate may adjust
9. Thermostat satisfied
10. Burner off
11. 15-second purge
12. Blower off 60-240
sec. later
Copyright 2019 Carson, Dunlop & Associates Ltd.
1. CABINET
Same as any furnace:
• Rust?
• Damage?
• Out of level?
• Combustible clearances –
negligible
Copyright 2019 Carson, Dunlop & Associates Ltd.
2. COMBUSTION AIR
• Also called dilution and ventilation
air
• Inside – need lots of space
• Outside - direct vent – pretty
straightforward~ish
• Note: Many furnaces can get
combustion air from in or out
Copyright 2019 Carson, Dunlop & Associates Ltd.
3. BURNERS
• Typically in-shot/monoport
• Not ribbon
Flame should be -
• Mostly blue
• Stable
• No lift off or floating
Copyright 2019 Carson, Dunlop & Associates Ltd.
ANY PROBLEM HERE?
Photo courtesy of HVAC-Talk.com. and Kenny Hart
Copyright 2019 Carson, Dunlop & Associates Ltd.
3. BURNERS
• 1 stage, 2 stage, modulating
• Not infinitely variable
• Does house air fan speed change as firing
rate changes?
• Does induced draft fan speed change as
firing rate changes?
Copyright 2019 Carson, Dunlop & Associates Ltd.
3. BURNERS
• 1 stage, 2 stage, modulating
• Not infinitely variable
• Does house air fan speed change as
firing rate changes? YES
• Does induced draft fan speed change as
firing rate changes? YES for most
Copyright 2019 Carson, Dunlop & Associates Ltd.
3. BURNERS
Burners at top of furnace – Why?
1. Better heat transfer - Coolest
exhaust gas meets coolest
house air
2. Condensate runs down – away
from burner
Copyright 2016 Carson Dunlop and Associates Ltd.
BURNERS AT TOP
Coolest exhaust
sees coolest
house air
(upflow)
Condensate
collected at
bottom, far from
burners
Cool
House
air
flow
War
m
Copyright 2019 Carson, Dunlop & Associates Ltd.
4. IGNITION SYSTEM
No standing pilots!
Most use one of these
–Hot Surface Ignition (HSI)
• most popular
–Direct Spark Ignition (DSI)
–Intermittent Pilot (IP)
Copyright 2019 Carson, Dunlop & Associates Ltd.
4. IGNITION SYSTEM
Hot Surface Igniters (2,500°F)
–Silicon carbide
–Silicon nitride (newer/more
durable/less energy)
Copyright 2019 Carson, Dunlop & Associates Ltd.
4. IGNITION SYSTEM
• Early Hot Surface Igniters
(HSI) were troublesome
• Newer ones are more
reliable
Copyright 2019 Carson, Dunlop & Associates Ltd.
5. HEAT EXCHANGER
• May be 1, 2 or 3 heat exchangers
• Most new furnaces have two
• 1st conventional steel or aluminized
steel
• 2nd plastic coated or stainless
• Sees harsher environment –
condensate
Copyright 2019 Carson, Dunlop & Associates Ltd.
5. HEAT EXCHANGER
• What is warranty on heat
exchangers?
• Can’t see cracks or clogging
• Small heat exchangers may clog
– Construction dust!
• Carbon/soot at exhaust termination
• May see evidence of leak below
Copyright 2019 Carson, Dunlop & Associates Ltd.
SOME DO RUST!Photo courtesy of HVAC-Talk.com. and Kenny Hart
Copyright 2019 Carson, Dunlop & Associates Ltd.
SOME DRAMATICALLY!
Photo courtesy of HVAC-Talk.com. and Kenny Hart
Copyright 2019 Carson, Dunlop & Associates Ltd.
RUSTED, CRACKED
HEAT EXCHANGERPhoto courtesy of HVAC-Talk.com.
Copyright 2019 Carson, Dunlop & Associates Ltd.
Soot on
the filter
is a clue
Copyright 2019 Carson, Dunlop & Associates Ltd.
6. CONDENSATE SYSTEM
• Need to condense
exhaust gases to get
efficiency
• Latent heat of vaporization
Copyright 2019 Carson, Dunlop & Associates Ltd.
6. CONDENSATE SYSTEM
• Highest efficiency at startup!
–Don’t need long running
cycles
–Cold heat exchanger makes
for good heat transfer
Copyright 2019 Carson, Dunlop & Associates Ltd.
6. CONDENSATE
• Where do we collect it?
–2 or 3 places
• How does it flow?
–Gravity mostly
Copyright 2019 Carson, Dunlop & Associates Ltd.
6. CONDENSATE
• Can make >1 quart in 30 minutes
• Again, 200 gallons/month
Copyright 2019 Carson, Dunlop & Associates Ltd.
7. INDUCED DRAFT FAN
• No dilution air
– Use 50% less air
• Pulls Combustion air in > Burner > Heat
Exchanger
• Pushes exhaust > Vent
• Heat exchanger more restrictive
– Get more heat out of the exhaust
Copyright 2019 Carson, Dunlop & Associates Ltd.
You don’t need a picture of an
induced draft fan, do you? ½ way
Copyright 2019 Carson, Dunlop & Associates Ltd.
7. INDUCED DRAFT FAN
•Early systems not so
reliable
•Better now
Copyright 2019 Carson, Dunlop & Associates Ltd.
7. INDUCED DRAFT FAN
• Plastic housing > metal
• Listen for bearing noise – squeaking,
grinding
Copyright 2019 Carson, Dunlop & Associates Ltd.
7. INDUCED DRAFT FAN
• Listen for splashing/gurgling on start-
up
– Condensate collection problem
– Low spot in venting system
Copyright 2019 Carson, Dunlop & Associates Ltd.
8. AIR PROVING SYSTEM
• Makes sure fan is moving air
• Combustion and exhaust
• Pressure switches
–Fixed
–Differential
Copyright 2019 Carson, Dunlop & Associates Ltd.
8. AIR PROVING SYSTEM
• Not much to check
• If problems, furnace won’t run
Copyright 2019 Carson, Dunlop & Associates Ltd.
WHERE’S AIR PROVING
SWITCH?
Where’s
the air
proving
device?
Copyright 2019 Carson, Dunlop & Associates Ltd.
9. CONTROL BOARD
–Complex/expensive black box
–Solid state
–Diagnostic LEDs
–3 year warranty typical
–Poor location!!!!
–$700 to replace????????????
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• PVC or ABS typical
• S636 White – 150ºF (PVC typically)
• S636 Grey - 200ºF (CPVC typically)
• Required since 2007
• Roof or sidewall
• 2 to 4 inch diameter typical
Copyright 2019 Carson, Dunlop & Associates Ltd.
POLYPROPYLENE VENT
• S636 rated
• 230ºF rating
• 6 ft lengths
• Push-fit connectors (no adhesive)
• Light, thin wall
• Flexible available for vertical only
• Grey, white, black for outdoor pieces
Copyright 2019 Carson, Dunlop & Associates Ltd.
POLYPROPYLENE VENT
Male ends face upstream
Only approved by some furnace manufacturers
Courtesy of Centrotherm
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• May be coaxial/concentric with
combustion air intake
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Vent length
• Lots of variables
• Minimum 15 ft typical – Why?
• Minimum 12 inch offset inside
home – Why?
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Minimum 15 ft typical – Why?
• Minimum 12 inch offset inside
home – Why?
May get water at termination
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Question runs > 40 feet
• Question > 3 or 4 elbows
• Elbows add ~5 feet each
• Larger diameters = longer runs
• Vertical can be longer than
horizontal
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Slope for sidewall systems
• To outside or back to
furnace?
• How much slope?
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Slope for sidewall systems
• To outside or back to
furnace? Furnace
• How much slope? ¼ in./ft.
Copyright 2019 Carson, Dunlop & Associates Ltd.
IF VENT SLOPES
DOWN TO OUTSIDECourtesy: hankeyandbrown.com
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Termination – Roof– 18 inches above roof (12 inches above snow)
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Termination – Sidewall – see manual!• 12 inches above snow level (Not grade!)
• Not over walkway
• 4 feet from gas regulator
• 6 feet from mechanical air inlet
• 4 feet from other air inlet beside vent
• 12 inches above air inlet below vent
• 12 inches from windows or doors
• Not right under eaves/No inside corner
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Vent should be insulated in unheated space
(e.g. attic, garage, cantina/cold room)
• Direct vent system – both go thru roof or
wall (same pressure zone)
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Often close together, side by side
(e.g. 3 in. for roof, 6 in. for wall)
• Exhaust often 12 in. above inlet
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Wall termination – see manual!
• Varies by manufacturer
• Vent may have to extend out at least 12 in.
• Point straight out
Copyright 2019 Carson, Dunlop & Associates Ltd.
10. VENTING SYSTEM
• Intake should be as short as possible
• Often points down
• Inspection tip – look for carbon/soot at
vent termination
Copyright 2019 Carson, Dunlop & Associates Ltd.Photo courtesy of HVAC-Talk.com. and Kenny Hart
Keep manual handy!
Copyright 2019 Carson, Dunlop & Associates Ltd.
11. HOUSE AIR FAN
• Most are multi/variable speed
• May be ECM/Brushless DC
• More efficient – uses <1/2 the electricity
Copyright 2019 Carson, Dunlop & Associates Ltd.
11. HOUSE AIR FAN
ECM Motors
• Run cooler
• Wide operating range
• Multi-stage furnaces
– operate faster with higher firing rates
Copyright 2019 Carson, Dunlop & Associates Ltd.
11. HOUSE AIR FAN
• ECM adds to furnace cost ~ $500?
• Energy savings
• $200/year often claimed
• May be true if AC
• More if fan always on
• Some studies say buy if fan always on
• Costs are down & warranties are up
Copyright 2019 Carson, Dunlop & Associates Ltd.
11. HOUSE AIR FAN
• Adjust fan speeds to get right temperature rise
• Rise too low? Slow fan down
• Rise too high? Speed fan up
Copyright 2019 Carson, Dunlop & Associates Ltd.
Watch Temperature Rise!
Hi-efficiency replaces conventional/mid
• Ductwork may be restrictive
• Air conditioning coil restricts flow
• May be hard to get adequate airflow
• Excess temperature rise voids warranty
• Modify ductwork?
Copyright 2016 Carson Dunlop and Associates Ltd.
12. SAFETY DEVICES
1. Limit switch
2. Rollout switch
3. Air proving switch
4. Flame sensor
5. Blower door
interlock
Copyright 2019 Carson, Dunlop & Associates Ltd.
12. SAFETY DEVICES
1. Limit switch
–Shut off on high temp
–Most auto reset
–Near burner or top of heat
exchanger
–Remember Fan/Limit switches?
Copyright 2019 Carson, Dunlop & Associates Ltd.
12. SAFETY DEVICES
2. Rollout switch
(Spillage switch, heat switch)
–Detects flame coming out of the
burner instead of into the heat
exchanger
–Shuts down furnace
Copyright 2019 Carson, Dunlop & Associates Ltd.
ROLLOUT
SWITCH
Copyright 2019 Carson, Dunlop & Associates Ltd.
12. SAFETY DEVICES
3. Air proving switch
(differential pressure switch)
• Makes sure air flows from intake
right through to vent termination
Copyright 2019 Carson, Dunlop & Associates Ltd.
12. SAFETY DEVICES
4. Flame sensor/rod/electrode
• Replaces thermocouple
• Proves flame in 2 – 8 seconds
• Often dirty – white crust
• Corrosive environment
– Kitty litter!
– Paint, laundry detergent
Copyright 2019 Carson, Dunlop & Associates Ltd.
Where are they?
Roll-out Switch Igniter Flame Sensor
Copyright 2019 Carson, Dunlop & Associates Ltd.
12. SAFETY DEVICES
5. Door interlock
–Prevents furnace operating with
cover off
–Handy for us!
Copyright 2019 Carson, Dunlop & Associates Ltd.
SIMPLE APPROACH
1. Inspect first
– Rust, leaks and age (size?)
2. Then test operation
– Fire up properly?
– Leaks, splash, gurgle?
– Shut down too soon?
– Temp rise after 15 minutes?
– Airflow at supply/return grilles
3. Suggest annual maintenance program
Copyright 2019 Carson, Dunlop & Associates Ltd.
Annual Maintenance
• But it has a 10-year warranty!!!!
• Prevention better than cure
• Diagnostic visit is not warranted
• Overtime is not warranted
• Warranty void if maintenance is poor
• We always recommend a contract