Why the Cheaper HVAC Bid Cost This Project $2.72M

On a recent multifamily development, the mechanical bid that looked cheaper on paper would have cost the project $2.72 million more to build. The lower number was a VTAC system. VTAC units are inexpensive to buy and simple to install, but they do not have great energy efficiency. In a performance path, that low efficiency does not stay in the mechanical room. It walks straight to the envelope and starts writing checks. The same building with ducted mini-splits cleared code with a far cheaper envelope, and the gap between the two paths was $2.72 million.

The Real Comparison

We modeled the same building two ways and held everything constant except the heating and cooling system. One path used VTAC units. The other used ducted mini-splits. Both had to pass the same energy code target, so the question was never which system looks more efficient on a spec sheet. The question was what each system forced the rest of the building to spend to reach compliance.

The VTAC path only cleared code once the envelope was loaded up to compensate. That meant triple-pane windows, heavy continuous insulation, and tight air sealing. None of that was about comfort or durability on this building. It was there for one reason, to buy back the performance the VTAC units gave away.

The ducted mini-split path cleared the same target with double-pane windows, no continuous insulation, and code minimum air sealing. Same building, same code, a dramatically lighter envelope. Everything the VTAC path had to add, the mini-split path got to skip.

Add up the envelope the VTAC path required, subtract the envelope the mini-split path avoided, and the difference was $2.72 million. The mechanical bid was lower. The building was not.

The Efficiency Penalty

Here is the mechanism most bids miss. A performance path does not grade the HVAC system in isolation. It grades the whole building against a target, and every component trades against every other component. Efficient equipment earns margin. Inefficient equipment spends it. When the heating and cooling system is inefficient, the model comes up short, and the only place left to make up the difference is the envelope.

VTAC units sit at the inefficient end of that trade. They are packaged through-wall units chosen for low first cost and simple installation, and they deliver a lower seasonal efficiency than a modern heat pump. The unit sleeve also punches a hole in the wall assembly at every location, which is its own small thermal penalty. A ducted mini-split runs at a much higher efficiency across the heating season, so it hands the model a surplus instead of a deficit.

That surplus is the whole story. With the mini-splits handing back margin, the envelope was free to sit at code minimum and the building still cleared its target. With the VTAC units draining margin, the envelope had to overperform just to get the same building to the same line. Two identical buildings, two very different walls, and the only reason for the difference was the box in the mechanical closet.

The envelope is an expensive place to buy back performance. Triple-pane windows cost more per opening than double-pane, and on a multifamily building there are hundreds of openings. Continuous insulation is one of the most expensive and labor-intensive layers in a wall, adding material cost, install time, and detailing at every penetration and transition. Tight air sealing to an aggressive target takes the right product and the right crew. The VTAC path paid for all three. The mini-split path paid for none of them.

None of those envelope upgrades were something the developer set out to build. They were the toll for passing code with a weak mechanical system. The VTAC line item was cheaper, and it quietly moved $2.72 million onto three other line items where nobody was looking.

When VTAC Still Wins

VTAC is not always the wrong call. There are buildings and jurisdictions where the packaged unit is the right tool and the envelope penalty either does not show up or does not matter.

Buildings that never enter a strict performance path. In a base code jurisdiction with no stretch or specialized target, the model is not forcing the envelope to chase the HVAC efficiency, so the trade that hit this project never triggers.

Projects where duct routing is impossible or brutally expensive. Some renovations and tight floor-to-floor structures cannot absorb ducted equipment without gutting the design. When ducts are off the table, the comparison changes and the packaged unit may be the only realistic path.

Buildings where the heavy envelope was already the plan. If triple-pane windows and continuous insulation were already specified for acoustics, durability, or a certification target, the VTAC path is not adding that cost, it is inheriting it, and the penalty largely disappears.

Transient occupancy that rewards simple per-room control. Hotels and similar uses value the independent, per-room simplicity of a packaged unit, and the operating pattern can make the efficiency gap matter less than it would in year-round housing.

The Decision Framework

If you are choosing a mechanical system on the install bid alone, you are pricing one line item and ignoring the three it moves. On this project the VTAC bid was cheaper in the mechanical closet and $2.72 million more expensive everywhere else, because the envelope had to carry what the equipment could not.

The way to catch that before it is priced into the wall is to model the systems against the same target and let the envelope respond to each. The cheaper box and the cheaper building are different questions, and only the model answers the second one.

This does not make VTAC wrong or mini-splits right on every job. A different code target, a different structure, a different set of envelope specs already on the drawings, and the numbers move. The point is that the mechanical decision and the envelope decision are the same decision, and the only way to know what the trade costs on your building is to run both paths before you lock the spec.