MEP Design for a Medical Office Build-Out: From a Small Suite to a Surgical Floor

Two medical offices, two very different jobs

"Medical office" covers a wide range. At one end is a practice of a few exam rooms and offices on an upper floor of a shopping street; at the other is an outpatient facility with operating rooms, recovery beds and medical gas. The MEP design for both has to give every room the right air, water and power, but the size of the job depends almost entirely on what the practice does in its rooms.

This guide uses two projects we designed in Queens, New York. The Astoria medical office is about 770 ft² on the second floor of an existing building. The Forest Hills outpatient facility is a new building of seven levels, with six operating rooms below the street.

How the two compare

Start with what happens in each room

A practice of exam rooms, consulting rooms and offices is close to an ordinary office in MEP terms: the main job is comfort, fresh air and a thermostat in each room. Procedures change that. Sedation and surgery bring medical gas, higher outdoor-air rates, pressure monitoring, humidity control and support rooms for sterilization and soiled materials, and each of those adds equipment, shafts and power. Before any sizing, we confirm:

• Which rooms are for consultation and examination, and which are for procedures
• Whether sedation or anesthesia is used, and so whether medical gas is needed
• Imaging, sterilization or laboratory equipment, with its cut sheets
• How many rooms need their own temperature control
• Opening hours, so the system schedule matches the practice
• What the landlord allows on the roof, in the shafts and on the facade

HVAC: a thermostat in every room

Patients undress in exam rooms, staff work at desks next door, and reception fills and empties through the day. Medical offices therefore need room-by-room control even when the suite is small. The two projects solved it in different ways.

Fresh air and exhaust

A small suite can often take its outdoor air through the wall. In Astoria, a 36 × 18 in. louvre feeds a mixing box with motorized dampers (300 to 1,250 cfm of outdoor air), a matching relief louvre with a barometric damper lets the same air leave, the toilets have 75 cfm exhaust fans interlocked with the lights, and a duct smoke detector stops the unit.

A building that sits mostly below the street cannot. In Forest Hills, six 7-ton and one 16-ton gas-fired rooftop units with hot-gas reheat and economizers carry the outdoor air for the clinical floors, with MERV 7 pre-filters and MERV 13 final filters, and three wheel-type energy-recovery ventilators pre-condition the outdoor air for the rest of the building. The outdoor air and exhaust were scheduled room by room, and the totals show where the demand is:

Procedure rooms: air changes, pressure and humidity

Once surgery is involved, the ventilation follows the healthcare criteria for surgical spaces rather than office rates. In Forest Hills, each of the six operating rooms (410 to 594 ft²) gets four air changes of outdoor air per hour, about 250 to 360 cfm each, through MERV 13 filtration. Pressure sensors and monitors watch the operating rooms and the spaces around them, and two electric-steam humidifiers of 12 lb/hr each hold 50% relative humidity at 68°F.

The 3,620 ft² pre- and post-operative area gets two air changes of outdoor air per hour, about 1,090 cfm, and the soiled workroom, sterilization and decontamination rooms have their own exhaust. That is why one level, the surgical suite, takes more than half of the building's outdoor air.

Medical gas

Medical gas is the item that most separates a procedure practice from an ordinary office. In Forest Hills, a dedicated riser serves the operating suite: a gas manifold fed from oxygen, nitrous oxide and medical-air supply tanks, an anesthesia scavenger and a vacuum machine, with exhaust vents routed outside. Every operating room has ceiling and wall outlets for oxygen, nitrous oxide, medical vacuum and waste anesthetic gas disposal, and the 13 pre- and post-operative beds have oxygen and vacuum.

The compressor, vacuum and gas-tank rooms were laid out with the mechanical and plumbing plans, because they need ventilation, drains and power of their own. For a dental practice, where vacuum, compressed air and nitrous oxide reach every chair, see our dental clinic MEP guide.

Plumbing when the clinic is below the street

On an upper floor the plumbing for a medical office is usually limited to new fixtures and the condensate from the cooling units. In Astoria, the fan coil has a 3/4 in. condensate drain trapped to a code-approved receptor, with a secondary drain pan under the unit.

Below the street sewer, everything has to be pumped. Forest Hills has a triplex variable-speed booster set (65 gpm at 145 ft of head) with an 86-gallon diaphragm tank, two 100-gallon gas-fired water heaters with a recirculation pump and thermostatic mixing valves at the fixtures, a duplex sewage ejector of 300 gpm at 25 ft for the waste from the lower levels, and sump pumps for the elevator pits and the garage drains, all with high-level alarms. Floor drains have electronic trap primers so their seals do not dry out.

Power for every piece of equipment

Even when the electrical design is by others, the mechanical and plumbing equipment has to be scheduled with its voltage, phase, minimum circuit ampacity and overcurrent protection, so the electrical contractor can size the feeders, disconnects and starters. Some of the connections we scheduled:

Fire protection

In an existing sprinklered building, new partitions usually mean the sprinkler layout has to be revised so every new room is covered. In a new building, the question is whether the city water supply can reach the top of the system. In Forest Hills, the hydrant flow test gave 50 psi static and 48 psi at 500 gpm, while the sprinklers and hose stream need 520 gpm at 60.3 psi, so a fire pump with a jockey pump makes up the difference. The building has a 6-inch combined sprinkler and standpipe riser, a second standpipe, dry-pipe zones for unheated areas and two fire department connections on the street.

Energy code and DOB filing

Both projects were filed with the NYC Department of Buildings together with an energy-code document. For the Astoria alteration, the COMcheck report shows the 40 kBtu/h split system at 13.0 SEER against the 13.0 required under the 2020 NYStretch Energy Code, filed with six mechanical sheets and two energy sheets in September 2024. For Forest Hills, the COMcheck analysis covers mechanical and service water heating under the 2020 NYC Energy Conservation Code (the water heaters are 97% efficient against 80% required), and we also prepared the backflow prevention applications for the fire and domestic water services and the revised mechanical, plumbing and sprinkler sets for filing in June 2024.

For when COMcheck is enough and when a full energy model is needed, see COMcheck vs ASHRAE 90.1 Appendix G.

What to send

To scope the MEP design for a medical office build-out, we need:

• The architect's floor plans, or the lease plan if the layout is not drawn yet
• A list of the rooms and what happens in each one
• Cut sheets for imaging, sterilization and other equipment
• Whether sedation, anesthesia or medical gas is planned
• The landlord's rules for roof equipment, shafts, louvres and penetrations
• What the building already has: sprinklers, the electrical service, and the gas and water supply

Our medical office work

We design medical offices and outpatient facilities in New York from a single trade to the full MEP and fire protection set, with the HVAC load calculation, energy compliance and DOB filing sets. See MEP engineering in New York, or send your plans for a free project review.