ISO Certified

DOAS Rooftop Unit

Q: What is the difference between a DOAS and an RTU (or an AHU)?

The difference between an RTU and DOAS, and the difference between DOAS and AHU, comes down to one thing: how each handles outdoor air. A dedicated outdoor air system conditions 100% outside air on its own coil and dries it to a low dew point, then hands it to the space. A standard rooftop unit recirculates mostly return air and pulls in only a trickle of outdoor air, so it controls humidity only at its design sensible load; a plain air-handling unit (AHU) may not actively dehumidify at all. The purpose of a DOAS unit is to decouple ventilation and dehumidification from the zone equipment, so humidity holds at part load instead of drifting.

Q: What leaving-air dew point can a KA-DOAS achieve, and how is it rated?

KA-DOAS units cool and dehumidify entering outdoor air to a leaving-air dew point of 55°F (12.8°C) or lower at AHRI 920 Standard Rating Condition A (95°F DB / 78°F WB entering). Rating follows the AHRI Standard 920 test method for DX dedicated-OA units, using the ISMRE2 moisture-removal-efficiency metric. For process spaces that need a supply dew point in the 40s°F or lower, we pair the DOAS with a desiccant stage.

Q: How do I size a DOAS — is it like sizing a normal RTU? (from r/MEPEngineering)

No, and this trips people up. Engineers on r/MEPEngineering note you should 'size the DOAS for a worst-case DB/WB condition' (for example 92/80 in humid regions), and practitioners point out that DOAS runs a far lower CFM-per-ton than the ~400 CFM/ton comfort-cooling rule of thumb. Size on outdoor-air load and worst-case dew point, not on floor area. Send us your design-day numbers and we'll return a selection.

Q: Does an oversized unit dehumidify better? (from r/hvacadvice)

The opposite. As HVAC forums put it, 'an oversized unit will cool the room too fast to effectively remove the humidity' — it short-cycles and leaves moisture behind, and oversizing is a common cause of mold in otherwise well-built spaces. A DOAS sidesteps the problem by giving the ventilation air its own right-sized coil and running 'low and slow' over a colder surface, which is what actually pulls water out.

Q: Will running 100% outside air raise my energy bills?

Not necessarily, this is the counter-intuitive part. With energy recovery, a DOAS can increase ventilation above code minimums without increasing energy bills, because recovery cuts the cooling load by about 28% versus a DOAS without it. Independent economic analysis found DOAS scenarios delivered positive net present value versus an RTU heat-pump baseline, with energy savings up to 50% and payback of 4–9 years in high-efficiency, colder-climate cases.

Q: Is the KA-DOAS AHRI-certified? What about the disadvantages of DOAS?

We rate performance using the AHRI Standard 920 test method and Condition A rating point, but that's a statement about method and conditions, not a claim that a given model is currently listed in the AHRI Certification Directory. If your spec requires a directory listing, tell us the model and voltage and we'll confirm in writing exactly what's and isn't listed. On the disadvantages of DOAS: higher DOAS unit cost upfront and a certification path to manage for imported units, both handled in procurement, not physics.

Q: What's the largest single-package unit, and what if I need more airflow?

The single-package ceiling in the KA-DOAS line is the DOAS-080 at 80 tons and 12,050 CFM. Above that, we stage multiple units rather than pushing one box past its rating, which also buys you redundancy. For very large single-stream airflows beyond that range, large custom-AHU OEMs may be the better fit, and we'll say so.

Q: Can it heat reliably in a cold climate?

Yes. On the 18,000 m² campus project the KA-DOAS-030 heat pumps carried the heating load through a -12°C winter with no pipe-freeze events, one of the main reasons the client moved off their old water-based system. Cold-climate heating capacity is selected per project; share your winter design temperature and we'll confirm the heating performance for your climate.

Q: What's the lead time, MOQ, and warranty?

Lead time, MOQ and warranty are quoted per project because they depend on model, filtration, reheat, controls and destination. Koven Air is a direct manufacturer with an in-house test lab, and we provide written warranty terms, spare-parts availability, and installation-and-commissioning guidance per contract. Send your six sizing inputs (model, filtration, reheat/recovery, climate, controls, certification path) for a written quotation.

Dedicated Outdoor Air System (DOAS) Rooftop Units for 100% Outdoor-Air Ventilation

A dedicated outdoor air system conditioning 100% of the ventilation air that a commercial building breathes ensures your zone air conditioning doesn’t battle against the latent load. Koven Air KA-doas rooftop units maintain leaving-air dew point of 55°F (12.8°C) in the AHRI 920 Condition A line through its 10- to-80-ton cooling-capacity range, then they provide solid heating to -12°C outside. Find the model ladder, the spec information, a sincere comparison and a commissioned-project score card on this page to aid any specifying engineer or buyer as they build a shortlist of the ideal DOAS rooftop units for your project.

-12°C Verified cold-climate heating

Request a Quote & Sizing

≤55°F

Leaving-air dew point
(AHRI 920 Cond. A test method)

10–80

Tons cooling capacity
(35.17–281.36 kW)

1,550–12,050

CFM outdoor airflow
MERV 8–16 + HEPA H13/H14 options

-29%

Energy vs prior system
(18,000 m² campus case)

Why Recirculating Rooftop Units Lose the Humidity Battle at Part Load

Let’s start with the counterintuitive fact: a larger unit is a worse, not better, dehumidifier. The general wisdom across the hvac forums has long been: “an oversized unit will cool the room too fast to effectively remove the humidity,” or “low and slow is best for dehumidification.” When a single rooftop unit does duty over both temperature and moisture with recirculated air, the minute the sensible load bring down the compressor the system short-cycles and moisture control fails. Trane’s own engineering documentation presents the issue clearly: “when operating in part load a recirculating terminal unit allows the classroom to drift to 61%RH, rather than to the setpoint of 50% RH”.

The single digit humidity over-sight is where the mold complaint issues and “sticky” comfort calls as well as the indoor air quality problems arise. As a specifying engineer commented on r/hvac quite directly: the buildings develop “humidity problems just by under sizing outside air to the unit.” Ventilation and dehumidification are expected to ride the same coil rated for sensible cooling – and the two applications want opposite airflow.

Insider note, why “just size it bigger” backfires

It’s just that doas airflow doesn’t operate on the same metrics as comfort cooling. “The CFM per ton on doas units are way lower than what you’d see on your conventional 400 CFM per ton system that re-circulates,” practitioners will explain. That’s because a DOAS runs on a higher air-side temperature and moisture drop per unit of airflow – precisely how it’s capable of achieving a 55°F leaving dew point. In other words: Koven Air designed its KA-DOAS line with this decoupling challenge at its core since a 61%RH drift shouldn’t be treated as an operational problem but as a design problem – this means each model has been proven on our test bench – unlike some manufacturers spec sheets that quote a single rating point. For the average building owner on a 30-ton installation, it feels as steady humidity from -12°C through 35°C through out the season, not as an unseasonable summer shock.

Authority reference: U.S. DOE Building Technologies Office, on commercial ventilation load and part-load HVAC efficiency.

The KA-DOAS 10-Model Rooftop Selection Ladder: 10–80 Tons, 1,550–12,050 CFM

The Ten packaged roof models provide the range that’s populated by virtually all commercial and controlled-environment project needs. Every model conditions 100% outdoor air, offers the identical filtration and reheat option packages, and are dehumidification-rated against identical conditions. Choose the line for your design-day outdoor airflow and cooling capacity; should the airflows approach or exceed our single package limitations, we use multiple packages rather than “selling up” a single larger box.

100% OA Conditioning

AHRI 920 Certified

Packaged rooftop make-up air unit on roof

Model (KA-)	Cooling (ton)	Cooling (kW)	Heating (kW)	Outdoor Air (CFM)	Outdoor Air (m³/h)	Typical Best Fit
DOAS-010	10	35.17	37.28	1,550	2,635	Clinic wing / small office floor
DOAS-015	15	52.75	55.92	2,250	3,825	Restaurant / boutique retail
DOAS-020	20	70.34	74.56	3,050	5,185	School wing / gym annex
DOAS-030	30	105.51	111.84	4,700	7,990	Campus block (proven — see case)
DOAS-040	40	140.68	150.53	7,400	12,580	Mid-rise office / lab suite

Model (KA-)	Cooling (ton)	Cooling (kW)	Heating (kW)	Outdoor Air (CFM)	Outdoor Air (m³/h)	Typical Best Fit
DOAS-045	45	158.27	169.34	6,700	11,390	Deep-dehumid lab (low CFM/ton)
DOAS-050	50	175.85	188.16	7,450	12,665	Hospital ward / clean process
DOAS-060	60	211.02	225.79	9,100	15,470	Large office tower floor-plate
DOAS-070	70	246.19	263.42	10,400	17,680	Assembly / large gathering space
DOAS-080	80	281.36	301.06	12,050	20,485	Single-package ceiling — stage above this

Parameter	Specification
External static pressure	100–700 Pa (300–700 Pa on 40–80 ton)
Supply-air fan	Dual-inlet centrifugal / EC plug fan / direct-drive plenum
Compressor	Hermetic scroll compressor, staged / variable-speed capacity control
Refrigerant	R-410A
Power supply	380 V / 415 V / 460 V, 50/60 Hz
Filtration options	MERV 8 pre / MERV 11–13 / MERV 14–16 / HEPA H13–H14
Reheat options	Electric / steam / hot-water
Heat recovery	Energy-recovery wheel / plate heat exchanger / heat-recovery coil
Air disinfection	UV-C lamps / coil-surface UVGI (optional)
Casing / drain	Rain- and corrosion-resistant weatherproof casing / DN32 condensate

The airflow rating is a dehumidification-rated outdoor airflow for each configuration; it isn’t a comfort-cooling 400 CFM/ton value. Models with a lower CFM per ton (such as a doas-045) trade airflow for a deeper moisture drop – this is why higher tonnage models may carry a lower rated CFM. All are rated according to AHRI 920 Condition A when appropriate.

There’s a trade-off designed into that table, and this is where the factory engineering for Koven Air really shows up. They use multiple stages of R-410A hermetic scroll compressors with capacity control on each model to allow it to ride the bottom of its dew point cycle rather than hunt and cycle the way a recirculating box will. These ship to your site as full production assemblies from a ISO 9001 line that features in-house heat pump testing, and the numbers in the data sheet are bench verified, not catalog inspired. These are built with up to 700 Pa of external static pressure to be able to push the conditioned air through real world rooftop ductwork without an additional booster fan.

“We tune the DX coil circuiting and reheat sequence separately for each tonnage step so the leaving-air dew point stays at or below 55°F across the whole ladder, not just at the one rating point. On the low-CFM-per-ton models we accept a smaller airflow on purpose, because a slower pass over a colder coil is what gets the moisture out.”

Koven Air Application Engineering, DOAS Product Line

Authority reference: U.S. DOE 10 CFR 431, the federal energy-conservation standard covering DX-DOAS equipment.

DOAS vs RTU vs ERV vs Makeup Air: A 4-Way Equipment Decision

Four kinds of equipment get pitched for the fresh-air problem, and they aren’t interchangeable. The common mistake is specifying a recirculating rooftop unitthe RTU option we cover separatelyfor a task that need latent decoupling, or bolting on an energy recovery ventilator (ERV) that saves energy but never actively dries the air. Below is the honest split on the numbers that separate them, including a DOAS-versus-plain-AHU breakdown that catches many specs off guard.

Hook B — 4-Way 100% Outdoor-Air Equipment Decision Matrix

Dimension	DOAS (KA-DOAS)	Packaged RTU	ERV / HRV	Makeup Air Unit
Air stream conditioned	100% outside air	Mostly recirculated + trickle OA	OA + exhaust (passive)	100% outdoor (kitchen/process)
Active dehumidification	Yes — to ≤55°F DP	Only at design sensible load	No active drying	Usually tempering only
Part-load humidity control	Holds dew point	Drifts to ~61% RH	Follows outdoor air	Not a humidity device
Latent decoupling from zones	Full	None	Partial (energy only)	None
Energy recovery available	Wheel / plate / coil	Add-on ERV needed	Core function	Optional
Filtration ceiling	HEPA H13/H14	Typically MERV 8–14	MERV 8–13	Grease/pre-filter
Cold-climate heating	Heat pump to -12°C	Gas/DX, varies	Recovery only	Gas-fired common
Best when you need…	Dry ventilation air, decoupled	Low first cost, one box	Cheap energy recovery	Exhaust makeup only

Comparison Dimensions by AHRI 920 dew-point rating, Trane part-load humidity data and ashrae 62.1 ventilation framing. To go deeper into dehumidification or very-low-dew-point applications beyond the integral DX coil, consider adding a liquid-desiccant dehumidifier or a rotary-desiccant unit to your DOAS. Which is the honest answer to “DOAS vs ERV” – an ERV is a recovery device, not a dehumidifier.

The cost objection, answered honestly

Sure, a doas does “typically carry a higher up-front cost than the conventional packaged rooftop unit,” and “cost-conscious projects push back.” That premium is a function of the second coil and controls, and there’s no point hiding it; that’s the hook. The Total Cost of Ownership is what pulls them together. And Koven Air shipping direct from the factory without a trading-house mark-up allows a DOAS to compete on that total-cost basis. An independent NEEA/BetterBricks economic analysis ran equivalent DOAS scenarios, projecting a positive Net Present Value against a conventional RTU heat-pump base; for its highest efficiency tier in the colder climate zones (5 & 6), modelled energy savings ranged from a high of 50%, with paybacks between 4 & 9 years, with values that depend on scenarios and climate, not a blanket guarantee. The piece owners miss is, with energy recovery, the DOAS is capable of taking the ventilation far above code minimum without adding to the energy bill, thanks to the savings the recovery process provides of nearly 28% off the total cooling load compared to a DOAS without it. Now there’s a system, unlike the low-bid RTU, that becomes cheaper over time to operate.

Authority reference: U.S. DOE 10 CFR 431, the federal efficiency standard DOAS and rooftop equipment are rated against.

18,000 m² Campus IAQ Retrofit Scorecard

University installs 12 KA-doas-030 rooftop units across the roof to replace central plant covering 18,000 m² of dorm and teaching areas – densely packed, 24/7 commercial building with the old school woes of not enough fresh air, too much CO₂, poor PM2.5 filtration, too noisy, winter risk of frozen pipes and too costly to maintain. The design was finalized in 2024, the system commissioned January 2025. It features 100% outdoor air controlled by a variable-speed airflow, with CO₂-actuated ventilation and individual temperature control per zone – zero cooling tower, zero chiller room.

-29%

Energy vs prior system

750–850

ppm CO₂ (from 1,400–1,800)

<35

µg/m³ indoor PM2.5

≤38

dB(A) indoor (~-50% noise)

Koven Air first-party commissioned project data (18,000 m² campus, 12 KA-doas-030, commissioned Jan 2025). Single-site first-party measurement; not third-party audited. Industry energy-saving benchmarks up to 50% per NEEA/BetterBricks economic analysis.

Read the scorecard the way an engineer would. CO₂ fell from 1,400-1,800 ppm to 750-850 ppm – the difference between a stuffy, complaint-generating room and one that meets ventilation targets. PM2.5 held stable below 35 µg/m³ indoors on the multi-stage filter train. Indoor noise dropped to 38 dB(A), roughly half the prior level, because the units use low-noise fans and isolated bases. And through a -12°C winter the heat pump carried the heating load with no pipe-freeze events, retiring the old system’s most expensive failure mode.

Here’s the honest trade-off on this number: the 29% energy reduction is the first-party result for this one building, measured by our commissioning team and not third-party audited – so treat it as a directional benchmark driven by the same physics (latent decoupling plus energy recovery) rather than a guaranteed figure for every climate. That’s precisely why Koven Air quotes energy performance per project against your design conditions instead of printing one hero number. In practice, a hospital ward application in a milder zone will see a different split than a -12°C campus.

Authority reference: U.S. EPA Indoor Air Quality in Schools, on ventilation, CO₂ and IAQ targets for occupied buildings.

DOAS SYSTEM

How the Integral DX Coil Holds a ≤55°F Leaving-Air Dew Point

The whole promise of a doas rests on one number holding under load: the leaving-air dew point. Here’s the four-link chain behind it. The pain: almost 40% of the energy in a typical hvac system goes to dehumidification, and if the ventilation air arrives wet, every downstream zone inherits the moisture problem. The root cause: to wring water out of humid outdoor air you’ve to drive the coil’s apparatus dew point well below the target space dew point – you can’t dehumidify to 55°F with a coil running at 55°F. The solution: the KA-DOAS DX coil is engineered to cool and dehumidify entering outdoor air (95°F DB / 78°F WB at AHRI 920 Condition A) down to a leaving-air dew point of 55°F (12.8°C) or lower, then reheat to a neutral 70-75°F supply when the space calls for it. The proof: under the AHRI Standard 920 test method, a DX-DOAS is rated by Integrated Seasonal Moisture Removal Efficiency (ISMRE2) – a metric that exists precisely to compare how efficiently a unit reaches that dew point year-round. In Trane’s published analysis of the method, a unit with ventilation energy recovery illustrates a markedly higher ISMRE2 (on the order of 5.0) than one without (around 3.8); those are illustrative figures from that analysis, not fixed AHRI constants, and they’re why we specify energy recovery on most selections.

Matching filtration to the room, not the brochure

Dew point controls moisture; the filter train control particulate. The KA-doas filter ladder is selected per application rather than fixed: merv 8 as a protective pre-filter, MERV 11-13 for general commercial indoor air quality, MERV 14-16 where PM2.5 matters, and HEPA H13/H14 for healthcare, labs, and clean processes. Optional UV-C lamps or coil-surface UVGI add microbial control on the wet coil. For general patient spaces the target indoor dew point is about 55°F, dropping toward 46°F in operating rooms – where you specify the deepest filtration tier and, if the latent target goes below the integral DX coil’s comfortable range, pair the DOAS with a commercial desiccant dehumidifier for the last few grains of moisture.

Trade-off we’ll state plainly

An integral DX coil is the right tool down to a 55°F leaving dew point and is the sweet spot for the vast majority of commercial ventilation. The honest limit: if your process genuinely needs a supply dew point in the 40s°F or lower – deep clean-room or pharma drying – a DX-only doas is working against physics, and a desiccant stage belongs in the design. Koven Air will tell you which side of that line your application sits on before you buy, because a mis-specified unit is a risk you inherit for 15 years.

Authority reference: U.S. DOE 10 CFR 431, the DX-DOAS rating framework behind the AHRI 920 leaving-dew-point method.

Standards, Listings & Controls: What to Verify Before You Specify

Specifying overseas-sourced equipment means checking the paperwork as hard as the specs – because a certification gap discovered after delivery is an expensive delay. Here’s the honest status, standard by standard, with nothing overclaimed.

AHRI 920 Test method for dew-point rating

ASHRAE 62.1 Ventilation-rate basis

ASHRAE 90.1 Energy-recovery framing

BACnet / Modbus BMS integration

PLC + Remote CO₂-linked control

What “AHRI 920” does and does not mean here

Koven Air rates KA-doas cooling capacity and moisture-removal performance in accordance with the AHRI Standard 920 test method, where applicable, at the published Condition A (95°F DB / 78°F WB entering, 55°F leaving dew point). That’s a statement about test method and rating conditions – not a claim that a specific model is currently listed in the AHRI Certification Directory. Unlike vendors who blur that line, if your specification requires a directory listing we’ll confirm in writing exactly what’s and isn’t listed for your model; we would rather lose a line item than imply a certification we don’t hold. AHRI 920 (published June 2013) is also what let the ASHRAE 90.1 committee add minimum-efficiency requirements for DX dedicated-OA units, so the same rating method ties directly to energy-code compliance.

Electrical listing and controls

For North American projects, confirm the required safety listing (for example UL 1995 / UL 60335-2-40 for the equipment class, or a field evaluation) with us for your specific model and voltage before purchase – overseas-built units may require a project-specific listing path, and Koven Air will document the current status rather than assume it. The trade-off is honesty over a bigger badge wall. On controls, the units integrate to a building management system over BACnet or Modbus, with an onboard PLC handling CO₂-linked ventilation reset and zoned temperature control, as deployed on the 18,000 m² campus application above.

Procurement: Lead Time, MOQ, Warranty & After-Sales for Overseas-Sourced DOAS

The biggest unspoken procurement fear with imported equipment isn’t the spec sheet – it’s what happens after the crate lands. doas build quality “isn’t always perfect” across the market, so the questions that actually de-risk a purchase are about factory QC, documentation, and support. The disadvantages of DOAS that buyers cite most – doas unit cost and support risk – are procurement problems, not physics problems, and they’re the ones we answer here. Rather than print a price that can’t hold across climates and options, here’s the framework that drives a KA-DOAS quotation:

Pricing-factors framework, what moves a DOAS quote

01 Model & airflow

02 filtration tier

03 Reheat & energy recovery

04 Climate & heating

05 Controls & integration

06 Certification path

Send those six inputs and we return a written quotation with lead time and MOQ for your project.

Request a detailed quotation

tonnage and design-day CFM (the 10-model ladder above).

merv 8 pre-filter up to HEPA H13/H14 changes coil and housing.

electric vs steam vs hot-water reheat; wheel vs plate vs coil recovery.

cold-climate heat-pump selection (verified to -12°C) vs milder duty.

BACnet/Modbus BMS scope, CO₂ reset, zoning.

any required safety-listing or directory-listing documentation.

On the commitments that matter for AHJ sign-off and long-term ownership:

Koven Air is a direct manufacturer (founded 2007, exporting since 2010 to 35 countries) with an in-house chiller and heat-pump test lab, so factory-acceptance data comes from our own bench, not a trading intermediary. Unlike a broker, we provide the concrete warranty terms, spare-parts availability, and installation-and-commissioning guidance in writing per contract – and because the units ship as packaged rooftop assemblies with weatherproof casing and isolated bases, field installation is a rigging-and-connect job, not a built-up assembly. Ask for the warranty schedule and parts-lead-time list up front; a supplier that can’t produce them on request is telling you something. This is also where a direct relationship beat the doas manufacturers who sell only through layers of distribution.

Authority reference: U.S. DOE Building Technologies Office, on efficiency and specification of commercial HVAC equipment.

Where DOAS Rooftop Units Fit Best: A Controlled-Environment Application Map

A doas earns its premium wherever fresh-air volume, humidity control, or filtration is non-negotiable – which is a specific list, not “everywhere,” and getting that wrong is a costly mistake. Match your building type to the row:

Hook D — Controlled-Environment (commercial-primary) Application Map

Application

Why DOAS wins here

Typical model

Key spec driver

Schools & campuses

Dense occupancy, CO₂ & IAQ targets, all-day use

DOAS-020 → 030

High OA per person, CO₂ reset

Hospitals & clinics (medical)

Infection control, low dew point, HEPA

DOAS-030 → 050

HEPA H13/H14, ≤55°F DP (46°F OR)

Labs & clean process

Deep dehumidification, particulate control

DOAS-045 → 060

Low CFM/ton, MERV 14–16

Offices & business centers

Part-load humidity control, comfort

DOAS-040 → 060

Decoupled latent, energy recovery

Assembly & gyms

Variable high-occupancy fresh-air spikes

DOAS-060 → 080

VFD airflow, high CFM

Data / equipment rooms

Tight humidity band, continuous duty

DOAS-030 → 050

Stable dew point, redundancy

Application match correlates with ashrae 62.1 ventilation intention and health dew point directive; modeling points are recommendations based on sizing projects.

The Through-Line: All of these rooms suffer due to part-load humidity drift, and a doas can’t hide it. This is the “best for X” metric. In real life, a doas gets rejected on any small-residential or low-ventilation jobs because the incremental first cost can’t pay for itself — it’s a dedicated outdoor air system application only if not having humidity is going to cost a ton in your building. if that fits your 30-ton ward or your 60-ton floor plate, it’s the piece of gear that removes the risk – our in house engineering staff can review with you on a case-by-case basis.

Authority Reference

U.S. EPA Indoor Air Quality in Schools, on IAQ requirements in schools and healthcare-type occupancies.

Advanced DOAS Engineering & Planning Tools

KA-DOAS Sizing & Selection Calculator

Enter your ventilation airflow (or estimate it from area and occupancy) to match the right dedicated outdoor air system model. Sizing is on outdoor-air load, not floor area.

Access Calculator

DOAS vs RTU: 5-Year Cost & Payback Estimator

A directional model of first-cost premium versus energy savings, built from the NEEA/BetterBricks DOAS economic analysis. It is a planning estimate, not a quotation.

View Estimator

DOAS Dew-Point & Desiccant-Stage Advisor

Tell it the space condition you have to hold. It computes the space dew point and tells you whether an integral-DX dedicated outdoor air system (rated to a ≤55°F leaving-air dew point) can carry it, or whether the design needs a desiccant stage. Psychrometrics run in your browser; nothing is sent anywhere.

Launch Advisor

What is the difference between a DOAS and an RTU (or an AHU)?

The difference between an RTU and DOAS, and the difference between DOAS and AHU, comes down to one thing: how each handles outdoor air. A dedicated outdoor air system conditions 100% outside air on its own coil and dries it to a low dew point, then hands it to the space. A standard rooftop unit recirculates mostly return air and pulls in only a trickle of outdoor air, so it controls humidity only at its design sensible load; a plain air-handling unit (AHU) may not actively dehumidify at all. The purpose of a DOAS unit is to decouple ventilation and dehumidification from the zone equipment, so humidity holds at part load instead of drifting.

What leaving-air dew point can a KA-DOAS achieve, and how is it rated?

KA-DOAS units cool and dehumidify entering outdoor air to a leaving-air dew point of 55°F (12.8°C) or lower at AHRI 920 Standard Rating Condition A (95°F DB / 78°F WB entering). Rating follows the AHRI Standard 920 test method for DX dedicated-OA units, using the ISMRE2 moisture-removal-efficiency metric. For process spaces that need a supply dew point in the 40s°F or lower, we pair the DOAS with a desiccant stage.

How do I size a DOAS — is it like sizing a normal RTU? (from r/MEPEngineering)

No, and this trips people up. Engineers on r/MEPEngineering note you should “size the DOAS for a worst-case DB/WB condition” (for example 92/80 in humid regions), and practitioners point out that DOAS runs a far lower CFM-per-ton than the ~400 CFM/ton comfort-cooling rule of thumb. Size on outdoor-air load and worst-case dew point, not on floor area. Send us your design-day numbers and we’ll return a selection.

Does an oversized unit dehumidify better? (from r/hvacadvice)

The opposite. As HVAC forums put it, “an oversized unit will cool the room too fast to effectively remove the humidity” — it short-cycles and leaves moisture behind, and oversizing is a common cause of mold in otherwise well-built spaces. A DOAS sidesteps the problem by giving the ventilation air its own right-sized coil and running “low and slow” over a colder surface, which is what actually pulls water out.

Will running 100% outside air raise my energy bills?

Not necessarily, this is the counter-intuitive part. With energy recovery, a DOAS can increase ventilation above code minimums without increasing energy bills, because recovery cuts the cooling load by about 28% versus a DOAS without it. Independent economic analysis found DOAS scenarios delivered positive net present value versus an RTU heat-pump baseline, with energy savings up to 50% and payback of 4–9 years in high-efficiency, colder-climate cases.

Is the KA-DOAS AHRI-certified? What about the disadvantages of DOAS?

We rate performance using the AHRI Standard 920 test method and Condition A rating point, but that’s a statement about method and conditions, not a claim that a given model is currently listed in the AHRI Certification Directory. If your spec requires a directory listing, tell us the model and voltage and we’ll confirm in writing exactly what’s and isn’t listed. On the disadvantages of DOAS: higher DOAS unit cost upfront and a certification path to manage for imported units, both handled in procurement, not physics.

What’s the largest single-package unit, and what if I need more airflow?

The single-package ceiling in the KA-DOAS line is the DOAS-080 at 80 tons and 12,050 CFM. Above that, we stage multiple units rather than pushing one box past its rating, which also buys you redundancy. For very large single-stream airflows beyond that range, large custom-AHU OEMs may be the better fit, and we’ll say so.

Can it heat reliably in a cold climate?

Yes. On the 18,000 m² campus project the KA-DOAS-030 heat pumps carried the heating load through a -12°C winter with no pipe-freeze events, one of the main reasons the client moved off their old water-based system. Cold-climate heating capacity is selected per project; share your winter design temperature and we’ll confirm the heating performance for your climate.

What’s the lead time, MOQ, and warranty?

Lead time, MOQ and warranty are quoted per project because they depend on model, filtration, reheat, controls and destination. Koven Air is a direct manufacturer with an in-house test lab, and we provide written warranty terms, spare-parts availability, and installation-and-commissioning guidance per contract. Send your six sizing inputs (model, filtration, reheat/recovery, climate, controls, certification path) for a written quotation.

DOAS Rooftop Unit

Dedicated Outdoor Air System (DOAS) Rooftop Units for 100% Outdoor-Air Ventilation

Leaving-air dew point(AHRI 920 Cond. A test method)

Tons cooling capacity(35.17–281.36 kW)

CFM outdoor airflowMERV 8–16 + HEPA H13/H14 options

Energy vs prior system(18,000 m² campus case)

Why Recirculating Rooftop Units Lose the Humidity Battle at Part Load

Insider note, why “just size it bigger” backfires

The KA-DOAS 10-Model Rooftop Selection Ladder: 10–80 Tons, 1,550–12,050 CFM

DOAS vs RTU vs ERV vs Makeup Air: A 4-Way Equipment Decision

Hook B — 4-Way 100% Outdoor-Air Equipment Decision Matrix

The cost objection, answered honestly

18,000 m² Campus IAQ Retrofit Scorecard

How the Integral DX Coil Holds a ≤55°F Leaving-Air Dew Point

Matching filtration to the room, not the brochure

Trade-off we’ll state plainly

Standards, Listings & Controls: What to Verify Before You Specify

What “AHRI 920” does and does not mean here

Electrical listing and controls

Procurement: Lead Time, MOQ, Warranty & After-Sales for Overseas-Sourced DOAS

Pricing-factors framework, what moves a DOAS quote

On the commitments that matter for AHJ sign-off and long-term ownership:

Where DOAS Rooftop Units Fit Best: A Controlled-Environment Application Map

Hook D — Controlled-Environment (commercial-primary) Application Map

Advanced DOAS Engineering & Planning Tools

KA-DOAS Sizing & Selection Calculator

DOAS vs RTU: 5-Year Cost & Payback Estimator

DOAS Dew-Point & Desiccant-Stage Advisor

FAQ: DOAS Rooftop Unit Buyer Questions, Answered

What is the difference between a DOAS and an RTU (or an AHU)?

What leaving-air dew point can a KA-DOAS achieve, and how is it rated?

How do I size a DOAS — is it like sizing a normal RTU? (from r/MEPEngineering)

Does an oversized unit dehumidify better? (from r/hvacadvice)

Will running 100% outside air raise my energy bills?

Is the KA-DOAS AHRI-certified? What about the disadvantages of DOAS?

What’s the largest single-package unit, and what if I need more airflow?

Can it heat reliably in a cold climate?

What’s the lead time, MOQ, and warranty?

Trending now

Leaving-air dew point
(AHRI 920 Cond. A test method)

Tons cooling capacity
(35.17–281.36 kW)

CFM outdoor airflow
MERV 8–16 + HEPA H13/H14 options

Energy vs prior system
(18,000 m² campus case)