Greater Lansing

Bathroom exhaust fan testing

A fan that spins is not a fan that works — and the one fault that costs real money is invisible from the bathroom, because it is in the attic above it.

What is actually wrong

Almost everybody tests a bathroom fan by switching it on and listening. Noise is the one thing a failing fan is still good at. A unit can run, sound busy, and move so little air that the mirror still fogs and the paint still peels, because what matters is the airflow at the grille and nothing about the sound tells you that.

The number worth knowing is cubic feet per minute, measured at the grille with the fan running. The usual benchmark for a bathroom is fifty CFM for a fan you switch on and off. The point is not the figure in isolation — it is that fans are rated on a test bench against almost no resistance, and then get fitted to twenty feet of crushed flex duct with four bends in it. A fan sold as a hundred CFM can easily deliver a third of that once it is in a real ceiling.

The second half of the test is simpler and finds bigger problems: where does the duct actually go? It is supposed to end outside the building. A surprising number end in the attic, and a bathroom fan venting into an attic is not a ventilation fault, it is a water leak you switch on every morning.

Where this stops

When it is not a handyman job

This is at the top of the page rather than the bottom because getting it wrong costs you a wasted visit. Insured, and no contractor license is claimed or implied — the Michigan residential builder license is not held.

TESTING AND DUCTWORK, NOT HEATING AND COOLING. Michigan mechanical contractor licensing covers furnace and air conditioning work and that is not offered here. A bathroom exhaust fan, its duct and its termination are a different thing and are squarely ours.
THE ELECTRICAL LINE IS LIKE-FOR-LIKE ON AN EXISTING CIRCUIT. Swapping a fan on the wiring and switch already there is our work. A new circuit, a new switch position or anything inside the panel is licensed electrical work and is referred.
A NEW HOLE THROUGH A SHINGLED ROOF IS NOT OUR TRADE. Where a duct has to be given a proper outside termination, a gable or an eave is usually the better answer anyway; where it genuinely has to go through the roof covering, that part goes to a roofer.
This is not a mold inspection. If there is visible mold from years of a fan venting into the attic, you are told so and shown the photographs, and remediation is a licensed specialist.
A measured airflow figure is a measurement, not a code certificate. Where a rebate or an inspection needs a signed result, say so up front so the right paperwork is produced.

The work itself

What actually gets done

Measure the airflow at the grille with the fan running, so there is a number rather than an impression.

Follow the duct from the fan housing to where it terminates, and confirm that is outside the building and not an attic, a soffit cavity or a joist bay.

Check the outside termination has a damper and that the damper actually opens when the fan runs and closes when it stops.

Look at the duct run itself — crushed flex, sags holding water, disconnected joints, and the number of bends, which is usually why a good fan performs badly.

Check whether the fan is sized for the room at all, and whether it is switched in a way that means it ever runs long enough to clear the moisture.

Photograph what is found in the attic or the ceiling void, so the decision afterward is made on evidence rather than on a verdict.

This work sits inside Home Energy Assessment, which carries the invoiced price bands for the trade with the sample size printed beside every figure.

What it costs

There is no price list for this, and here is what actually decides the number.

The same three words describe a twenty-minute job and a two-day one. Rather than publish a figure that is wrong for one of them, here is what moves it — so you can work out roughly which end of it you are at before anybody comes out.

How many fans are being tested. A second and third in the same house cost far less than the first, because most of the visit is getting set up and getting into the attic.

Whether the attic above the bathroom can be reached and walked safely, which decides whether the duct run can be inspected along its length or only at its two ends.

Whether anything is put right on the same visit — reconnecting a dropped duct, freeing a stuck damper and sealing a joint are small jobs that are much cheaper done while somebody is already up there.

A replacement fan, if the one fitted turns out to be the problem rather than the duct, which is quoted separately with the unit at cost.

How to get a real number

Somebody comes out, looks at it properly, and you get a fixed price in writing with the work set out line by line and the exclusions written down as plainly as the inclusions. Coming out to do that is not charged for, and neither is working out what is wrong. If something is found once a wall or a floor is open, it is priced as a written change order and you decide before the work carries on rather than after it is billed. Materials are supplied at cost with the receipt attached, first-time customers get 10% off labor, and labor carries a one-year craftsmanship warranty.

If this is happening right now

What to do in the next five minutes, and what happens when you ring.

Before anybody arrives

Hold a single sheet of toilet paper against the grille with the fan running. If it does not hold up on its own, the fan is moving almost nothing and the rest of the test is a formality. If it does hold, that still only proves some air is moving, not enough.
Go outside and look for the vent while somebody runs the fan. If you cannot find a hood on a wall, a soffit or the roof, there is a fair chance there is not one.
Put your head in the attic hatch with a torch. A duct lying loose, or ending in a pile of damp gray insulation, answers the question on the spot.
Look at the ceiling around the fan and at the underside of the roof deck above it. Staining, rusted nail points or frost in winter all say the same thing.
Note how long you normally run it for. A fan switched off with the light is often switched off five minutes before it has finished the job.

Call the business line

(517) 505-7135

Answered Monday to Friday, 08:00 to 18:00. There is no out-of-hours line and this page is not going to invent one — outside those hours, leave a message with the address and what is happening, and it is picked up in the morning.

On the call you get asked what is happening, what else in the building is affected, and whether it is still getting worse. That is how it gets decided whether this is our job at all — and if it is not, you get told that on the phone rather than after somebody has driven out.

No trip charge
No call-out fee or minimum
No diagnostic fee
No charge for a return visit

True across all 84 written quotes this company has issued. Most contractors in this market charge to turn up.

Or send the details

When the right answer is not this company

You can smell gas: Leave the building and call the utility from outside. Not us, and not later.
Water you cannot stop: Your main shut-off first, then a licensed plumber. Every minute of this one costs money.
Sewage backing up, or several fixtures at once: A licensed plumber with a camera. That is the shared line, not a fixture, and a cable down one sink will not touch it.
Sparking, scorching or a burning smell at an outlet or a panel: Breaker off, and a licensed electrician. Electrical work here is repair and like-for-like replacement, and this is neither.
No heat, or heating and cooling equipment that has failed: A licensed mechanical contractor. That trade is not offered here at all, and knowing that in one phone call is worth more than a visit.

Questions people actually ask

My bathroom fan runs — why would it need testing?

Because running and working are different. The fan is rated on a bench against almost no resistance; what it delivers in your ceiling depends on the duct it was connected to, how long that run is, how many bends it has and whether anything has crushed or disconnected it since. Fans that sound perfectly healthy routinely measure a third of their rating. The mirror fogging, paint peeling off the ceiling or a window running with water are the symptoms people notice, and all three are airflow.

What does it mean if the duct ends in the attic?

It means every shower is putting warm wet air into a cold space where it condenses. Over a winter that soaks insulation, which then stops insulating, and over several it rots sheathing and grows mold on the underside of the roof. It is common — we found it twice in two weeks this October, both times in houses whose owners had no idea. Putting it right is reconnecting the duct and giving it a real outside termination, and the cost of that is nothing next to what it prevents.

How much air should a bathroom fan move?

Fifty CFM is the usual benchmark for a fan you switch on and off, with larger bathrooms wanting more. What matters more than hitting a number exactly is whether the room actually clears: if the mirror is still fogged ten minutes after a shower and the fan has been running the whole time, the fan is not keeping up whatever its label says.

Can you just replace the fan?

Often, and sometimes that is the right answer. But fitting a bigger fan to the duct that was strangling the old one buys you a louder disappointment, which is why the duct gets looked at first. If the unit genuinely is the problem it is replaced like-for-like on the existing circuit, with the fan at cost.

Is this part of a home energy assessment?

It is one of the things checked in a full assessment, because a fan dumping into an attic is both a moisture problem and a hole in the building. You can also have it done on its own, which is what most people want when the symptom is a bathroom that will not dry out.

Have your bathroom fan tested

Tell us how many bathrooms have fans and whether the attic above them can be reached. Before you book, try the single sheet of toilet paper against the grille — if it will not hold up on its own, say so, because that tells us the answer before we arrive. If you already know the duct ends in the attic, say that too and we will come ready to put it right on the same visit.

Get a Free Quote Call (517) 505-7135