DOAS + Hydronics: The Upgrade That Stops Paying to Push Air Around

Most office buildings still operate on an old idea: use air to do everything.

One large air handler pushes air through long ducts to heat, cool, and ventilate every space. It’s familiar. It also creates a predictable set of owner problems: uneven comfort, noisy tenant complaints, humidity issues, high fan energy, and limited control when occupancy changes.

This matters now because operating cost volatility is no longer theoretical. Energy prices move. Tenants compare buildings more aggressively. And “good enough” comfort is less acceptable when leases get harder to win and keep.

A DOAS + hydronic approach is one of the cleanest ways to reduce operating friction: let air do air’s job (fresh ventilation) and let water do heat’s job (moving heating/cooling).

1) The business problem with “all-air” systems

Owners don’t replace systems because they dislike old equipment. They replace systems because the asset starts losing money in quieter ways:

·       Fan energy stays high year-round (even when loads are low)

·       Zones fight each other, leading to hot/cold calls and overrides

·       Humidity control is inconsistent, especially in shoulder seasons

·       Ventilation is either under-delivered at peak occupancy or wasted when spaces are empty

·       Operators spend time chasing complaints instead of managing performance

In short: the building “works,” but it doesn’t operate cleanly.

Over time, that shows up in higher OPEX, more staffing burden, and lower tenant confidence.

2) The core shift: separate ventilation from heating/cooling

A more current approach splits the job into two systems that do what they’re good at:

·      DOAS (Dedicated Outdoor Air System):Delivers 100% outdoor air for ventilation, filtered and conditioned, to the right places in the right amounts.

·      Hydronics (water-based heating/cooling):Uses water to move heating and cooling to zones via fan coils, radiant, heat pumps, or other terminal strategies.

The owner-relevant point: moving heat with water is far more efficient than moving heat with air (per unit volume, water carries thousands of times more heat than air). That often translates into lower fan horsepower, smaller ducts, quieter operation, and better zone stability—assuming the system is designed and controlled well.

3) Where the savings and comfort gains come from

Owners should be wary of “percent savings” claims without context. The real drivers are specific and measurable:

·      Lower fan energyAll-air systems pay a large “air-moving tax.” DOAS reduces how much air you have to push around for heating/cooling.

·      Better part-load performanceMost buildings spend most hours at partial load. Hydronic delivery often handles partial loads smoothly without over-ventilating.

·      Humidity control that isn’t accidentalDOAS can be designed to manage latent loads (moisture) more deliberately than all-air approaches that depend on coincidental coil conditions.

·      Improved zone controlThermal comfort becomes a zone-level hydronic issue, rather than a building-wide duct distribution compromise.

·      Cleaner ventilation controlVentilation becomes a controlled service (right air, right place, right time), not a byproduct of heating/cooling delivery.

If you’re upgrading for NOI stability, these mechanisms matter more than a headline number.

4) Integration is where projects succeed or drift

DOAS + hydronics is not automatically “smart.” It becomes valuable when the systems are coordinated through controls.

A well-integrated strategy typically defines:

·       how ventilation responds to occupancy (or schedules) without overreacting

·       how humidity limits are managed (and what “limits” actually mean for your tenant mix)

·       how supply air temperature and flow are reset over time

·       how terminals and central systems avoid fighting each other

·       what alarms matter, and what operator response is expected

Without clear sequences, the project can land in a common failure mode: safe-but-wasteful operation, where airflow and temperatures are held constant to prevent complaints, and the owner pays the bill.

5) Data helps—when it’s designed for verification, not dashboards

Instrumenting a building isn’t the goal. Verifying performance is the goal.

Owners get real value when the design includes:

·       the right trend points (flows, temps, humidity, valve positions, unit status)

·       a commissioning plan that proves sequences work

·       an “as-operated” baseline so the building can be managed after turnover

Analytics and AI can help later. But if the project can’t prove basic sequences and control stability first, “AI optimization” becomes noise. Owners should demand proof before promises.

6) Retrofit realities owners should plan for

For existing buildings, DOAS + hydronics is not a single decision—it’s a packaging decision:

·       Space and routing: where ducts and piping go (and what that does to leasable area)

·       Electrical capacity: especially if heating is moving toward electrification

·       Tenant disruption: phased work vs. empty-floor work vs. after-hours premiums

·       Envelope and air leakage: ventilation strategies don’t fix a leaky building; they can expose it

·       O&M readiness: operators need a playbook, trend visibility, and training that matches the system

This is where owner advocacy matters. A good concept can still turn into an expensive outcome if constructability and operations aren’t planned early.

7) The owner decision: what you’re really buying

A DOAS + hydronic upgrade isn’t “new mechanical equipment.”

It’s a shift toward:

·       lower operating cost volatility (especially fan energy and over-conditioning)

·       fewer comfort-driven overrides

·       better humidity and ventilation control

·       a building that can be tuned and verified, not just “run”

That’s why the best way to evaluate it isn’t a brochure. It’s a business case tied to:

·       your hold period

·       your tenant profiles

·       your planned leasing strategy

·       your risk tolerance for disruption and complexity

8) What smart owners do next

If you’re considering this approach, here’s the owner-grade path that avoids the usual mistakes:

1.     Start with the operating problem, not the equipment (comfort complaints, fan energy, humidity, ventilation control, staffing burden)

2.     Require a controls narrative early (sequence of operations that matches your outcomes)

3.     Treat commissioning as proof (pass/fail testing tied to sequences, not “it looks fine”)

4.     Insist on trend points that verify performance (so optimization isn’t guesswork)

5.     Build a phasing plan that protects leasing (tenant disruption is often the real cost driver)

Takeaway

Most older buildings spend too much money pushing air around to do jobs air isn’t good at. DOAS + hydronics can be a strong owner move when it’s treated as an operating strategy you can verify—not a technology swap. The upside is real: lower friction, better controllability, and a building that holds its performance instead of slowly drifting.