Where can I place my heat pump's outdoor unit, and what noise, permit, and HOA rules apply?

What the rule says

There is no single national rule for where an outdoor heat pump unit may go or
how loud it may be. The rules come from four places, all local: the zoning
code (setbacks, height, and screening for outdoor equipment), the noise
ordinance (decibel limits and measurement methods), the mechanical and
electrical permit requirements, and — in HOA or condominium communities — the
governing documents and architectural review. The ENERGY STAR air-source
heat pump reference
explains how heat pumps work, ducted versus mini-split systems, and proper
sizing (a contractor should verify system size with a "Manual J" calculation),
but ENERGY STAR certifies efficiency, not placement or noise; those are decided
by local rules.

The verified examples below show how concrete these local rules are. The City
of Portland Residential Mechanical Permits page
requires a mechanical permit for work on heating or cooling systems, including
HVAC systems, furnaces, heat pumps, air conditioning condensing units, and
mini-split systems, and adds that a mechanical permit is still required even if
a building permit is not. It also states that outdoor mechanical equipment —
including outdoor air conditioner units and heat pumps — is not allowed in the
required front zoning setback, is allowed within a side or rear setback in
most residential zones, and, if within a setback, cannot be more than five
feet high and must be hidden from neighbors using walls, fences, or
vegetation.

On the noise side, the New York City DEP exterior HVAC noise-control guidance
sheet
states that NYC Noise Control Code section 24-227 sets the following limits:
42 dBA Lmax (slow) for a single air-circulating device and 45 dBA Lmax
(slow) for the cumulative noise level of multiple air-circulating devices,
both measured within the receiving property at a distance of three feet from
the open portion of a window. Enforcement of the Noise Code is shared by the
Department of Environmental Protection and the NYPD, and complaints are filed
through 311, per the NYC Noise Code page
and the DEP's summary guide to the Noise Code.

Which authority controls

Each layer of authority operates independently, and none of the sources
reviewed here waives another:

• Zoning codes control where the unit sits on the lot — Portland's
  front-setback prohibition and five-foot/screening rule for units within a
  setback are an example, not a national standard.
• Noise ordinances control how loud the unit may be at a neighbor's
  property. New York City's 42/45 dBA limits at three feet from an open window
  illustrate how specific these can be; other cities use different limits,
  distances, and measurement scales (dB versus dB(A)).
• Mechanical and electrical permits apply independently of zoning and
  noise rules. The City of San Diego Mechanical Permit page
  states that no part of heating, ventilating, air conditioning, or
  refrigeration systems shall be installed, altered, replaced, or repaired
  unless a mechanical permit has been obtained, and offers a Simple "No-Plan"
  mechanical permit for minor installations — including installations of
  forced-air or A/C units and replacement of furnaces — on non-historic
  properties, with a plan-required path for other work. Portland separately
  notes that you will need to apply for an electrical permit for most
  mechanical equipment projects.
• Association governing documents control appearance and placement in
  HOA, condominium, and co-op settings through architectural review. None of
  the sources reviewed here overrides them. The official sources reviewed for New York did not identify a specific statewide protection. Local law,
  governing documents, contracts, and general property law may still affect
  the result.

What may still be required or restricted

• Manufacturer clearances and installer requirements. The ENERGY STAR
  reference directs buyers to have a contractor size the system (Manual J) and
  confirm the right unit for the climate; the outdoor unit's required
  clearances to walls, walkways, and property lines come from the
  manufacturer's installation instructions and the installer's design, and
  local codes may adopt or enforce them.
• Screening and aesthetics. Portland's within-setback screening rule
  (walls, fences, or vegetation) reflects a common local expectation; HOA or
  condominium appearance rules can be similar or stricter.
• Historic and designated properties. San Diego's no-plan mechanical
  permit path is limited to non-historic or potentially designated properties;
  historic districts typically add their own review layers.
• Common areas and shared property. In condominiums and co-ops, outdoor
  units on common walls, roofs, or shared yards are controlled by the
  association's rules and the unit's location relative to other owners'
  interests.
• Documentation and measurement methods. Where noise is at issue, the
  measuring method matters: NYC's limit is measured at the neighbor's open
  window, and Portland's noise-documentation guide
  explains that smartphone readings are educational only and are not used for
  official purposes — a certified and calibrated sound level meter is the
  official instrument.

Facts that could change the answer

• The city and its code values. NYC's 42/45 dBA limits, Portland's
  five-foot/screening rule, and San Diego's permit tiers are local rules with
  different numbers and structures; another city's noise ordinance, setback
  table, or permit path will differ.
• The property type. Detached homes, HOA-controlled homes, townhomes, and
  condominiums are governed differently; common-area or shared-wall
  installations add association rules.
• The exact equipment. A single outdoor unit, multiple units (NYC's 45 dBA
  cumulative limit), a mini-split, or a ducted system can land in different
  categories under local rules.
• Code changes in progress. Portland's noise program notes a Noise Control
  Code amendment project; limits can change, so check the current text.
• The measurement context. Background (ambient) noise, distance, and
  whether the reading uses dB or dB(A) can change whether a unit is compliant,
  as the NYC summary guide's discussion of sound measurement explains.

Practical decision path

1. Read the local zoning code for the lot and confirm where outdoor mechanical
   equipment is and is not allowed (setbacks, height, screening).
2. Read the local noise ordinance and note the exact limit, measurement
   distance, and scale (dB vs dB(A), Lmax window) that apply to HVAC equipment.
3. Ask the building department which permits apply — in the cities reviewed, a
   mechanical permit is required for heat pump and mini-split work, and an
   electrical permit is usually needed too.
4. If the property is in an association, review the governing documents and
   submit the architectural application before installing; keep the written
   decision.
5. Get the manufacturer's published sound rating for the unit and choose a
   location that respects the local limits — NYC's guidance recommends
   selecting equipment with lower noise ratings and avoiding placement near
   noise-sensitive receptors.
6. If noise becomes a dispute, document it per the local method (for example,
   Portland's 15-day log with dBA/LAmax readings, or NYC's 311 complaint
   process) before spending money on fixes.

Before work begins, obtain the written requirement from the local building, electrical, zoning, fire, or utility office and keep the record.

Records to keep

Keep the zoning research for the lot, the noise ordinance text with its
measurement method, the mechanical and electrical permit applications and
approvals, the manufacturer's sound rating and installer specifications, the
association governing documents and written approval or denial, and any noise
documentation you create — dates and times, patterns, dBA/LAmax readings, the
meter or app used, and complaint reference numbers. These are the records a
code official, association, or court will use to test the installation against
the applicable rules.

When professional advice may help

Placement and noise disputes combine zoning, Building code, noise-ordinance,
and association-law questions. Consider asking the local building department
about the permit path and setback rules before designing the installation; an
acoustical consultant, as NYC's guidance recommends, where compliance with a
decibel limit is disputed; and an attorney familiar with the property's state
and local law before starting work over an objection or pursuing an
enforcement claim.