ACC Building Performance LLC

08/25/2026

HVAC-Related Condensation:
When You Can Blame the HVAC Contractor and When You Can’t

We get called into homes all the time for HVAC-related condensation, especially condensation occurring on equipment and ductwork installed in attics.

And the first reaction is almost always the same:

The HVAC contractor screwed up.

Now, I’m not saying HVAC contractors aren’t stupid. We all know plenty of them are. This industry gives us more than enough examples every day.

But you cannot automatically blame the HVAC contractor every time an HVAC system sweats.

Sometimes the system is failing.

Sometimes the environment you put the system in is the failure.

There is a very important difference.

The Vented Attic Problem

When HVAC equipment and ductwork are installed in a vented attic in a hot, humid climate, that attic is essentially outdoors.

Southeast Louisiana. South Florida. The Gulf Coast. Pick your poison.

Outdoor dew points here are routinely brutal.

And a vented attic can sometimes experience moisture conditions even worse than the outdoor environment because moisture generated inside the house can migrate upward, adding to the moisture already entering from outside.

Now think about what we do next.

We install one of the most critical and moisture-sensitive systems in the entire house inside that environment.

We take ductwork carrying air somewhere around 50 to 55 degrees, wrap it in marginal insulation, connect it together with dozens or hundreds of seams, fittings, collars, plenums, boots, flex connections, access panels, refrigerant penetrations, and drain assemblies, and stick the whole thing in a hot, high-dew-point attic.

Then everybody acts surprised when it sweats.

Bam.

Condensation.

That is not necessarily an HVAC equipment failure.

That is physics.

You Cannot Blame the System for Making Cold Air

An air-conditioning system is supposed to remove heat from the house.

That means portions of the equipment and distribution system are going to be cold.

You cannot blame the AC system because the air coming out of it is cold.

And you cannot automatically blame the HVAC contractor because the equipment he installed is actually doing what it was designed to do.

If the system is operating reasonably, producing the proper temperature drop, moving the right amount of air, removing moisture from the conditioned space, and otherwise performing as intended, but the exterior surfaces of the equipment and ductwork are below the dew point of the attic air surrounding them, you have an environmental problem.

Not necessarily an equipment problem.

The system did not create that attic environment.

It is simply reacting to it.

“We’ve Always Done It This Way”

This is where the famous construction industry excuse comes into play:

“We’ve always done it this way.”

Exactly.

And we have always had problems.

Putting HVAC systems in vented attics has been common practice for decades.

Common does not mean correct.

If you install cold HVAC equipment and ductwork in a vented attic in a hot-humid climate, condensation should not shock anyone.

I would argue you should expect it.

Physics always wins.

And when water shows up, you better start paying attention.

Because where you have persistent water, you dramatically increase the potential for microbial growth, material deterioration, corrosion, insulation damage, and eventually major building failure.

We Put the Most Important System in the Worst Place

Think about how ridiculous this really is.

The HVAC system is arguably the most important mechanical system in the house.

It plays a major role in:

Moisture control
Dehumidification
Ventilation
Filtration
Pressure relationships
Air distribution
Indoor air quality
Comfort
Durability

It influences nearly everything associated with the indoor environment.

Yet we routinely install this sophisticated, moisture-sensitive equipment in the most hostile environment available.

The attic.

Then, when it fails, we blame the guy who installed it exactly where the house was designed for him to install it.

That does not always make sense.

So What Do You Do in an Existing Home?

In a retrofit situation where the HVAC equipment is in a vented attic and condensation is occurring, the first question should be:

Is the HVAC system actually malfunctioning?

If the answer is no, and the condensation is occurring because surface temperatures are falling below the surrounding attic dew point, you basically have two choices.

Bring the HVAC system into the house.

Or bring the house into the attic.

Moving an entire HVAC system and duct distribution network into conditioned space can be extremely intrusive and expensive in an existing home.

In many retrofit applications, the more practical solution is to move the building enclosure.

Encapsulate the attic.

Move the primary air and thermal boundary from the ceiling plane to the roofline.

Now the HVAC system is no longer sitting outside.

The attic becomes part of the building enclosure, and the moisture conditions surrounding the equipment can actually be controlled.

But this is where the responsibility changes.

The Encapsulated Attic Changes Everything

Once the attic is encapsulated, whether through spray foam, a properly designed double-roof assembly, or another method of moving the primary air and thermal boundary to the roofline, the attic is no longer functionally outside.

The HVAC system is now inside the building enclosure.

The attic air is part of the indoor environment.

And now I absolutely will blame the HVAC contractor.

Why?

Because the HVAC contractor’s responsibility is to gain control of the air mass inside the house and maintain that control.

And his number-one priority in a hot-humid climate should be moisture control.

If the HVAC contractor installs equipment in an encapsulated attic and allows attic dew points to remain high enough that the equipment, ductwork, registers, plenums, or other cold surfaces repeatedly condense, that is no longer simply an unfortunate interaction between cold equipment and outdoor conditions.

That is a failure to control the indoor air mass.

The attic is now part of the house.

It is inside the pressure boundary.

It is inside the thermal boundary.

Its moisture conditions must be controlled.

If they are not, somebody failed to properly design, install, commission, or operate the mechanical system responsible for controlling that environment.

And yes, in that situation, the HVAC contractor deserves a whole lot more scrutiny.

The Difference Is Responsibility for the Air

This is really what the entire argument comes down to.

In a vented attic, the HVAC contractor does not control the attic air.

The attic is outside the building enclosure.

If the HVAC system is performing properly but sweating because it is surrounded by extremely humid air with a high dew point, blaming the HVAC contractor simply because the ductwork is cold misses the larger problem.

The building put the HVAC system in a hostile environment.

In an encapsulated attic, the situation is completely different.

That attic is now part of the controlled environment.

The mechanical system has responsibility for that air.

And if that air is not being adequately dehumidified and controlled, the HVAC design has failed one of its most fundamental responsibilities.

Stop Diagnosing Condensation by Looking at the Water

Condensation is not the diagnosis.

Condensation is the symptom.

You have to determine why the surface temperature crossed the dew point.

Was the duct insulation damaged?

Is there excessive air leakage?

Is the system producing abnormally low supply-air temperatures?

Is airflow restricted?

Is the attic vented and sitting at an 85-degree dew point?

Was the attic encapsulated without any strategy whatsoever for controlling its moisture?

Is outdoor air infiltrating?

Is the building under negative pressure?

Is the dehumidification strategy inadequate?

Those answers determine responsibility.

Not the puddle of water on the attic floor.

The HVAC contractor is not automatically innocent.

And he is not automatically guilty.

Understand where the air and thermal boundaries are.

Understand who controls the air surrounding the HVAC system.

Understand the dew point.

Understand the surface temperature.

Then blame the right problem.

Because whether anyone wants to admit it or not, condensation still follows physics.

And physics does not care who sent the invoice.

08/21/2026

08/16/2026

https://youtu.be/Em2HJ4CXews?si=iUVQoFgCSHBVXwZ3

Three doctors compare how they diagnose, test, and treat mold toxic...

08/10/2026

Indoor Air Quality, Broken Down in Its Simplest Form

Indoor air quality gets made way more complicated than it needs to be.

There are endless products, gadgets, air cleaners, UV lights, ionizers, monitors, sprays, coatings, certifications, and marketing claims all promising to make the air in your home healthier.

But when you strip all of that away, healthy indoor air comes down to four basic principles.

AJ's KISS for Indoor Air Quality.

Keep It Super Simple.

The Four Pillars of Indoor Air Quality
1. Moisture Control

Moisture kills houses, and it kills us in the process.

If you do not control moisture, almost everything else you do for indoor air quality becomes secondary.

High indoor humidity, condensation, bulk-water intrusion, wet building materials, poorly controlled crawlspaces, vented attics in humid climates, oversized HVAC equipment, duct leakage, and uncontrolled outdoor-air infiltration all create conditions that allow biological growth and building deterioration.

The goal is not simply to cool the house.

The goal is to keep the building dry.

That means controlling indoor relative humidity, managing bulk water, controlling v***r movement, keeping building materials from reaching conditions that support microbial growth, and designing the HVAC system around latent moisture removal, not just temperature.

In a hot-humid climate, moisture control has to be intentional.

You cannot accidentally get this right.

2. Source Control

The second principle is simple:

If it's toxic, don't bring it into the house.

Obviously, that is impossible to accomplish completely.

Modern homes are filled with manufactured materials. Flooring, cabinets, furniture, paint, adhesives, cleaning products, fragrances, plastics, mattresses, textiles, insulation, sealants, and hundreds of other products can introduce chemicals into the indoor environment.

We are never going to eliminate every contaminant.

But we can dramatically reduce the load.

Choose lower-emitting building materials and finishes whenever possible. Be intentional about furniture and textiles. Pay attention to cleaning products, fragrances, pesticides, solvents, and other chemicals brought into the home.

Do not intentionally introduce pollutants and then try to buy a machine to remove them afterward.

Source control comes first.

The less contamination we introduce into the house, the less we have to manage later.

3. Effective Filtration

This is where people often tell me:

"I already have a really good filter."

Then I look up and see a one-inch filter shoved into a return grille in the ceiling.

That is not effective filtration.

Filtration is a system.

For filtration to work properly, the duct system has to be tight enough that the air entering the HVAC system actually passes through the filter.

No return leaks pulling attic air into the system.

No filter bypass around the edges.

No poorly fitted filter racks.

No giant gaps between the filter cabinet and air handler.

All of the air going through the system needs to go through the filter.

MERV 13 as a minimum and MERV 16 when practical.

But there is an important catch.

You cannot simply install a restrictive high-efficiency filter into an HVAC system that was never designed for it.

The filter cabinet, return ductwork, blower, airflow, and available static pressure all have to be considered during the design.

A great filter installed in a terrible duct system is not great filtration.

It is just a great filter.

4. Ventilation

Finally, we need controlled mechanical ventilation.

Homes produce pollutants constantly.

People breathe. We cook. We clean. We shower. Furniture and building materials off-gas. Indoor activities generate particles, carbon dioxide, moisture, odors, and chemicals.

The answer is dilution.

But I do not want random outdoor air leaking through cracks in the walls, attic, crawlspace, recessed lights, electrical outlets, or other holes in the building.

I want outdoor air brought into the house on my terms.

I tell it when to come in.

I tell it how much to bring in.

I filter it.

I dry it.

And I distribute it properly throughout the home.

That is ventilation.

Not random infiltration.

Not opening a window and hoping for the best.

Controlled mechanical ventilation.

Notice What I Did Not Say

I did not say UV light.

I did not say photocatalytic oxidation.

I did not say bipolar ionization.

I did not say we need another gadget hanging in the ductwork supposedly "cleaning" the air.

None of those devices are one of the four pillars.

Why?

Because our goal is not to add crap to the air.

My goal is to take things out of the air.

That distinction matters.

Anytime someone sells you a device that intentionally introduces ions, reactive chemistry, oxidants, or some other process into your indoor air, you need to understand what you are actually buying.

What is that device producing?

What are the byproducts?

What happens when what it produces reacts with the chemicals already present inside the home?

What secondary chemistry is taking place?

In most homes, we already have an incredibly complex mixture of cleaning products, fragrances, off-gassing materials, cooking emissions, personal-care products, furniture, flooring, adhesives, and countless other chemicals.

I have no interest in intentionally creating additional chemistry in that environment unless there is a very good reason to do so.

And I certainly do not believe a gadget should become the substitute for proper moisture control, source control, filtration, and ventilation.

The fundamentals come first.

Actually, the fundamentals are the system.

You do not fix a moisture problem with an air purifier.

You do not fix contaminated return air with a UV light.

You do not fix poor filtration with an ionizer.

You do not fix inadequate ventilation with photocatalytic oxidation.

Stop trying to treat the symptoms with gadgets and fix the building.

That's It

Moisture control.

Source control.

Effective filtration.

Mechanical ventilation.

Those are the four pillars.

Get those four principles right and you have fundamentally changed what the indoor environment is doing to the people living inside it.

The home is no longer simply a shelter that happens to have an air conditioner.

It becomes an environment designed to promote health and wellness.

This is incredibly easy in concept.

There is nothing revolutionary about these four principles.

The hard part is ex*****on.

Getting the building enclosure, HVAC system, dehumidification, ductwork, filtration, ventilation, pressure relationships, materials, and controls to actually work together requires knowledge across multiple trades.

That is where most homes fall apart.

Everyone is responsible for their individual piece of the house, but almost nobody is responsible for how all of those pieces interact.

Indoor air quality does not need to be mysterious.

Control the moisture.

Reduce the sources.

Filter the air.

Ventilate intentionally.

Keep It Super Simple.

08/06/2026

The Ignorance That Is Costing Homeowners Their Health

Sometimes I wonder if I’m the crazy one.

I was originally hired to perform a comprehensive building performance assessment on a multi-million-dollar home because the homeowner was experiencing health issues and wanted to know if the home itself was contributing.

It didn’t take long to find the answer.

Over the decades, the home had accumulated layer after layer of poor renovations, improperly executed HVAC work, moisture problems, and building science failures. None of it happened overnight. It was the result of contractors doing just enough to get paid while no one ever looked at how the house actually functioned as a system.

After delivering my report, the homeowner decided to hire the same general contractor responsible for much of the previous work to make the repairs.

I couldn’t understand it, but there it is….

Eventually, I was hired as a consultant and to design a completely new HVAC+D system for the home. The design wasn’t based on what was easiest to install or what made the contractor the most money. It was based on building science and decades of field experience. A properly engineered rigid trunk-and-branch duct system with short flex runouts, inverter heat pumps, dedicated dehumidification, filtration, ventilation, and a complete strategy to control temperature, humidity, pressure, and airflow throughout the home.

The homeowner insisted on using the HVAC contractor recommended by the general contractor to install my design. From my interactions with him, it was obvious he was your typical residential HVAC sales tech. Nothing I’d seen suggested he had any understanding of building science or system design, but again, it wasn’t my decision.

Then the homeowner’s second house entered the conversation.

Her health wasn’t improving there either.

Before talking with me, she had the same HVAC contractor evaluate that home and recommend what needed to be done.

She called and asked for my opinion.

I asked to see the proposal.

It was exactly what I expected.

A new flex duct spaghetti mess.

A UV light.

An air scrubber.

An electronic air cleaner.

No engineering.

No investigation.

No discussion about why the house was making someone sick.

Just a list of products.

I told her that proposal was laughable and recommended performing a full assessment before spending a dollar.

When I assessed the house, the findings were staggering.

The home had been remodeled about seven to ten years earlier by the same general contractor.

Typical hackery.

The vented attic was loaded with condensation, contaminated insulation, decades of construction debris, knob-and-tube wiring, and a severe rodent infestation with f***s and urine throughout.

The home was built over a vented crawlspace where the entire subfloor showed widespread suspected microbial growth, along with several areas of wood rot.

Inside the home I found leaking windows and walls, rot beneath multiple windows, wet knee walls with suspected microbial growth on the backside, and numerous moisture-related deficiencies.

Yet somehow…

The recommendation was still a UV light, an air scrubber, an electronic air cleaner, and new flex duct.

That’s like putting a Band-Aid on a broken leg.

I prepared a comprehensive scope of work addressing the actual problems. It was extensive because the deficiencies were extensive.

When she received the proposal, she asked if I could remove some items to reduce the cost.

I respectfully declined.

I don’t remove necessary repairs just to hit a budget. If I know something needs to be corrected to protect the occupants and the home, I’m not going to pretend it doesn’t exist.

She ultimately decided the house wasn’t worth the investment.

That was her decision.

Fast forward a few weeks.

While visiting the primary residence, I overheard the general contractor’s carpenter talking about work that had been completed at the second house.

I asked the HVAC contractor what they ended up installing.

“A Rheem inverter.”

I asked if they encapsulated the attic.

“No.”

So they installed an inverter and furnace with flex ductwork throughout a vented attic in Southeast Louisiana.

Anyone who understands psychrometrics knows exactly where this story is headed.

When outdoor dew points routinely climb into the mid to upper 80s, vented attics become extremely harsh environments for HVAC systems. Lower supply air temperatures, long runtimes, and cold duct surfaces create the perfect conditions for condensation if moisture isn’t properly managed.

I didn’t argue.

I didn’t say a word.

Then it came time to move forward on the HVAC system for the primary residence.

The contractor reviewed my design and immediately said he wouldn’t install rigid ductwork because “metal duct sweats.”

Let that sink in.

He refused to install and warranty a rigid metal duct system located entirely inside a fully encapsulated, temperature-controlled, dehumidified attic because he believed the metal would sweat.

But he had absolutely no problem installing and warranting flex duct in a vented attic surrounded by 140-degree attic temperatures and 85-89°F dew points.

Read that again.

Rigid duct inside conditioned space?

“No. It’ll sweat.”

Flex duct in a vented Louisiana attic?

“No problem.”

This is exactly what’s wrong with our industry.

The people making recommendations often don’t understand the physics behind what they’re installing.

They’re repeating what they’ve always heard, not what they’ve actually measured or understand.

And homeowners don’t know the difference.

To them, every truck looks the same.

Every estimate looks professional.

Every contractor sounds confident.

Confidence isn’t competence.

Physics doesn’t care what you’ve always done.

Moisture doesn’t care how many systems you’ve installed.

Condensation doesn’t care what your salesman told you.

Building science always wins.

The only question is whether you’ll learn that before or after the damage is done.

08/06/2026

Boston, MA

08/01/2026

Complacency in a Dangerous Field Leads to Injury

During an assessment like so many others, I started finding deficiencies almost immediately.

This was a massive home, nearly 10,000 square feet, with approximately $300,000 invested in five brand-new Trane XV20i systems. The homeowner’s primary complaint was severe Dirty Sock Syndrome, so the HVAC equipment was a major part of my investigation.

I opened the first of the five air handlers and immediately found Trane UV lights shining directly onto the epoxy-coated coil.

That alone raised concerns.

I began documenting the equipment, its configuration, the UV exposure, and the conditions inside the air handler. This is an environment I know extremely well. I have opened and inspected more HVAC systems than I could ever count.

I understand that these units contain high-voltage electrical components, low-voltage controls, sharp metal edges, and powerful moving parts.

I know the hazards.

And somehow, that familiarity contributed to me getting severely injured.

I had completed my inspection of the first air handler and was preparing to close the unit when I noticed one more thing I thought I should check.

What happened immediately after that is still unclear.

I have relived every movement in my head a million times over the past two days. I remember inspecting the unit, documenting what I found, and noticing something else I wanted to look at before closing it up.

But the moments immediately before my fingers contacted the blower wheel are a blur.

I do not remember consciously deciding to reach farther into the unit. I cannot clearly explain where my hand was, what caused me to move it, or exactly how my fingers reached the wheel.

I only know that one second I was performing what felt like a routine assessment, and the next, the blower wheel had torn through the nail beds of my middle and ring fingers, down to the bone, and fractured the tips of both.

I was in the basement of a brand-new client’s $7 million home, hundreds of miles from home, bleeding heavily and in severe pain.

I ran upstairs dizzy and close to passing out, then had to ask a client I had just met to drive me to the nearest hospital.

That is a humbling position to find yourself in.

This did not happen because I lacked experience or did not understand the equipment. I knew exactly what was inside that air handler and what it was capable of doing.

Yet somehow, during a task that felt completely normal, I crossed the line between safe and severely injured without recognizing it.

That may be the most disturbing part.

Complacency is not always a conscious decision to ignore safety. Sometimes it is the absence of a conscious decision altogether.

Your hands continue moving while your mind is focused on the inspection, the deficiency, the photograph, or the next thing you want to verify. The work becomes automatic because you have performed similar tasks thousands of times before.

Then something happens in a fraction of a second, and afterward, you cannot even explain exactly how you allowed yourself to get into that position.

Experience is supposed to teach us how to identify hazards, but experience can also make those hazards feel familiar.

A blower wheel does not care how many licenses you hold or how long you have been in the trade. It does not care how comfortable you are around the equipment.

I knew better.

I still got hurt.

This is not a story I enjoy telling, but contractors need to hear it.

We work around electricity, refrigerants, combustion appliances, rotating equipment, ladders, attics, crawlspaces, roofs, power tools, and heavy machinery every day.

The work may feel routine, but the hazards are never routine.

Before reaching into equipment, shut it down.

Verify the power is off.

Confirm that all moving parts have completely stopped.

Do not assume a thermostat setting, control switch, or open panel has made the equipment safe.

No photograph, measurement, observation, or additional finding is worth a permanent injury.

I was fortunate.

The blower wheel could have taken my fingers completely. I could have contacted a high-voltage component, passed out alone in the basement, or fallen while trying to get upstairs.

This could have ended much differently.

So, to every contractor, technician, inspector, assessor, and tradesperson reading this:

Slow down.

Shut it off.

Verify it.

Protect yourself.

The moment the work becomes so familiar that you stop consciously respecting the danger is the moment you may be most at risk.

Complacency in a dangerous field leads to injury.

I learned that lesson the hard way.

07/19/2026

Some spray foam insulation wisdom from an industry leader.

Matt Risinger takes a balanced, evidence-based look at spray foam i...