Mecklenburg County Engineering & Building Standards
Mechanical Q & A 2000
Attention: 4 Denotes a new question!
General:
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August 2000
(Q) Should an inspector fail the residential HVAC mechanical contractor’s
inspection, for missing equipment or defects in the installation of a
secondary gas appliance installed by others (i.e. gas logs, gas grills, gas
lights, etc)?
(A) NO! Each contractor must stand on his own with respect to
inspection requests, inspections and there associated results.
(Exception; an inspector may elect to hold up the HVAC contractor’s
inspection on Jobs missing secondary permits).
(Q) What is the definition of a “Sleeping Room”?
(A) SEE INTERPRETATION (Dec, 1999)
(Q) Are installers/contractors allowed to cut wood framing when installing
or replacing HVAC systems?
(A) Yes! Provided that proper heading off of cut members/timbers is
properly completed. The mechanical inspector may require framing
to be inspected (permit) by the building inspector.
Are contractors required to run load calculations on the
installation/replacement of HVAC equipment?
(A) Yes! Load calculations are always required!
(Q) When should seismic concerns be addressed, in the field with a
contractor or during the design phase with the engineer?
(A) Seismic design is the responsibility of an engineer and shall be
submitted with the construction documents during plan submittal.
(Q) Is a contractor required to install the thermostat and all the register
the final mechanical inspection (residential)?
(A) The mechanical contractor is responsible for the installation of
the thermostat and registers. The contractor may elect to install the
thermostat at start-up to circumvent construction damage. The
registers are typically not installed until after all floor coverings are
installed. Due to construction schedules, these items may be
installed after the final mechanical inspection.
Mecklenburg County Engineering & Building Standards
Mechanical Q & A 2000
Equipment
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(Q) Is the bottom of a furnace required to be blanked off (sealed) when
utilizing side or rear returns?
(A) YES! Volume III section 605 and Volume VII section 1901 require
that duct systems be sealed and many manufacturers note the
blanking off or sealing of the bottom of equipment in their
installation instructions.
(Q) Can the primary drain of equipment installed in a crawl space, exit the
foundation “below exterior grade” and tie into a dry well or French drain?
(A) NO! The condensate drain must exit the foundation above grade
prior to connection to a French drain or dry well.
(Q) Can an approved gas decorative appliance (gas logs) be installed
under stairs in a residence/
(A) Yes! Gas appliance may be installed under stairs in a residence
provided that the walls/stairs are covered with 5/8” thick drywall and
sealed (mudded)
(Q) Is PVC cleaner required on condensate piping?
(A) Yes!
(Q) May wood be used to support the air handler when installed inside a
pan?
(A) DOI states that it is acceptable provided the equipment is
approved for zero clearance and the contractor uses treated wood.
(Q) May a manufacturer of a listed product, alter their installation
instructions by issuing a letter from their design engineer?
(A) No! A letter altering installation instructions of listed products
must come from the listing agency.
(Q) Is it permissible to install a float switch in addition to the installation of
a secondary condensate drain?
(A) Yes!
(Q) May an inspector disallow the use of a safety pan float switch in
instances where a conventional condensate drain could have been
installed?
(A) No! The contractor has the right to install whichever he/she may
choose.
Mecklenburg County Engineering & Building Standards
Mechanical Q & A 2000
Gas Piping:
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(Q) May an appliances 2 psi regulator (between the appliance and its gas
cock) be installed on the rough inspection?
(A) Yes!
(Q) What is the proper way to test a new set of gas logs installed on its
own 2 psi pipe system?
(A) Install a test gauge (30 lb max) on the end of the 2 psi system at
the meter location and pressure test back to the appliance. Placing
the 2 psi regulator under test is prohibited. A spool piece IS
REQUIRED to take its place.
(Q) Does the Code allow the use of flex gas pipe connectors on outside
appliances like a gas pack?
(A) Yes! Provided they are approved for exterior installations.
(Q)
Where is the correct place to install an appliance drip leg
(Furnace/Water heater)?
(A) Manufacturer’s installation instructions usually require the
sediment trap to be installed between the appliance and the 100%
cutoff.
(Q) What is the definition of conspicuous place as it is referenced in the
Code for condensate disposal?
(A) DOI States that it would be a place where you would not normally
see water discharging (i.e., eves, over doors or windows etc) It can
not discharge in the same location as the primary condensate drain.
(Q) Is the use of steel gas piping for protection allowed on CSST flexible
gas piping systems?
(A) No! Not at the present time.
(Q) Is the use of aluminum flexible conduit allowed in CSST gas pipe
systems?
(A) No! All CSST manufacturers require that “steel” flexible conduit
be used where referenced in their respective installation
instructions.
(Q) What type of protection is required on copper/CSST piping installed
outside a structure?
(A) Copper and CSST gas piping installed outside must be protected
with a PVC sleeve (schedule 40 min.) from a point 3 inches below
grade to a point 36 inches above grade. (per DOI letter)
Mecklenburg County Engineering & Building Standards
Mechanical Q & A 2000
Duct Systems:
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(Q) Are the inside seams of boots required to be sealed with mastic?
(A) NO! ALL seams in duct systems are required to be sealed but
nothing requires a boots seams to be sealed on the inside. The
contractor/installer may elect to seal the outside seams instead. The
downside is that an inspector reserves the right to spot check the
boot seams to assure they are sealed and this would require the
partial removal of the insulation.
It would then be the
contractors/installers responsibility to re-wrap the boot.
(Q) May the installation of polyethylene plastic to cover the exposed earth,
reduce the 4” duct clearance requirement of the Mechanical Code?
(A) NO! A minimu of 4” is required.
(Q) May 1.5” plastic web strap be used to support flex or fibrous duct?
(A) Yes! Note: (DOI is currently looking at the flame spread rating
and its applicability)
( Q) Is a sleeve required to join separate pieces of flex duct together?
(A) Yes! The Air Diffusion Council (ADC) requires that a joining
sleeve be used to connect separate pieces of flex duct. The liner is
required to be secured with 2 wraps of UL181 tape and then a
panduit strap is applied to the joint. The insulation wrap is secured
in place with either 2 wraps of UL181 tape or a panduit strap or both.
(Q) Does the Code allow flex duct to sag between hanger/supports?
(A) Yes! The flex duct may sag a maximum of ½ inch per foot
maximum.
(Q) May a contractor install/cut in a starting collar to a factory formed
radius fitting?
(A) No! SMACNA requirements would not allow the installation of
collars into a radius fitting.
(Q) When installing flex duct runs, what must the installer due with the
excessive flex?
(A) Excessive flex must be removed from each duct run. Flex runs
are required to be as direct as possible and ONLY the amount of flex
to complete the run and its required radiuses is to be installed.
May a single 16” flex duct be used for the supply or return on a 3 ton
(36,000 BTU) piece of equipment?
(A) No! Volume VII (1902.2 & 1903.1) requires the total unobstructed
area of a return or supply air ducts or openings to a central A/C unit
and/or heat pump shall be accordance with manufacturers
installation instructions, BUT NOT LESS THAN 6 INCHES FOR EACH
1,000 Btu/h NOMINAL COOLING.
(Q) How often must a boot be secured?
(A) The boot must be secured to the structure on at least two
opposing sides. A manufactured system is approved for use with
ceiling grids.
Mecklenburg County Engineering & Building Standards
Mechanical Q & A 2000
Duct Systems:
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(Q) Can white vinyl flex plastic pipe be used on bathroom exhaust fans?
(A) No! Work performed under volume III would require exhaust
duct to meet the requirements of chapter six (6) of volume III which
would require UL 181 flex duct or metal piping of a nonabsorbent,
moisture/corrosion resistant nature.
Note: Volume VII currently does not have a restriction on white vinyl
plastic pipe.
11) 4 (Q) May floor joists be panned and used as a return plenum?
(A) Yes! Provided they meet the requirements set forth in 1901.1.1
section 6. (i.e. isolation from structure utilizing tight fitting stops and
2” nominal (1.5” actual) wood.)
Mecklenburg County Engineering & Building Standards
Mechanical Q & A 2000
Venting:
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(Q) What is minimum clearance for B-Vent from combustible materials?
(A) The minimum clearance from combustible material (ie, wood,
shingles, drywall, etc) is 1”.