HVAC Duct Openings in Concrete: A Planning Guide

The short answer is: HVAC openings should be marked from the approved duct drawing, scanned for rebar and services, and then cut with a diamond core bit for round ducts and pipes or a wall or floor saw for rectangular ducts. Cutting with a breaker leaves ragged edges, cracks the surrounding plaster and makes the duct harder to seal, which shows up later as air leakage, condensation stains and noise.

Office fit-outs along Golf Course Road and Cyber City, new clinics, restaurants and even large homes now install ducted or VRV air-conditioning, fresh-air units and kitchen exhaust systems. Almost every one of these needs openings through RCC walls or slabs. This guide walks through how we plan those openings, which cutting method suits which duct, and what the HVAC contractor, the site engineer and the client each need to confirm.

Types of HVAC openings we cut

Most HVAC work involves a mix of small round holes and larger rectangular cut-outs. The general principles of air distribution are covered well in Wikipedia's article on ducts); what matters on site is the size, shape and position of each penetration.

• Refrigerant and drain pipe sleeves for VRV and split systems
• Round spiral duct openings for supply and return air
• Rectangular duct openings through walls and slabs
• Fresh-air and exhaust louvre openings in external walls
• Kitchen exhaust duct openings in restaurants and homes
• Riser openings in slabs for vertical duct runs

Round ducts and pipes: core drilling

Round penetrations are cut with a diamond core bit matched to the duct or sleeve size plus a small clearance for insulation and sealant. The rig is anchored to the wall or slab, water cools the bit, and the core comes out in one piece. Because the method is low vibration, it is suitable for occupied offices and apartments. Our diamond core bit sizes chart explains how hole size relates to pipe and duct size.

Allow for insulation

A common error is drilling exactly to the bare duct diameter. Insulated ducts and lagged refrigerant pipes need extra room, and fire-stopping or sealant needs a gap to fill. Confirm the final outer diameter with your HVAC contractor before the hole size is fixed.

Rectangular ducts: sawing with corner cores

Rectangular ducts are cut by drilling a core at each corner and sawing straight between them with a wall saw or floor saw. This gives square edges that the duct collar and flange can sit against neatly. Larger slab cut-outs are removed in sections so each piece can be handled safely. The method is explained in more detail in core drilling vs concrete sawing.

Checks before any HVAC opening is cut

HVAC openings are often larger than plumbing holes, so the checks matter more. We follow the same discipline described in our concrete cutting safety checklist.

• Confirm positions against the approved HVAC and structural drawings
• Avoid beams, columns and shear walls unless the structural engineer has approved the opening
• Scan for rebar, conduits and pipes inside the concrete
• Check what is below a slab opening and protect it
• Agree how the duct will be supported and sealed after cutting

Large openings in slabs or in load-bearing walls need a structural engineer's sign-off. Our article on structural approval for openings explains what to ask for.

Working in live offices and shops

Fit-outs often happen while neighbouring units are open. Wet diamond cutting keeps dust down, and we sheet floors, contain slurry and agree timings with the building management. Many commercial buildings ask for noisy work outside business hours and for a work permit in advance. We cover this in more depth in our guide to commercial fit-out cutting.

Coordinating with the HVAC contractor

The smoothest jobs are the ones where the HVAC contractor marks every opening on site, with the size written beside it, before we arrive. That avoids guesswork, keeps the visit short and means the ductwork team can start installing immediately afterwards.

After cutting: finishing and sealing

Once the duct or pipe is installed, the gap around it must be sealed. External wall openings need weatherproofing so rain does not track inside, and openings between floors or fire compartments need appropriate fire-stopping as specified by the project's consultant. Edge dressing and debris clearing are part of our core cutting services, and our article on post-cut repair and sealing covers the finishing side.

Planning tips that save time

• Batch all HVAC openings into one visit where possible
• Confirm lift access and working hours with building management
• Keep the area under slab openings clear and barricaded
• Share drawings or marked photos on WhatsApp before the visit
• Ask for any openings in finished false ceilings to be marked from above and below

You can see examples of commercial and residential openings on our projects page.