How to install fan in glass window?

Kingleviathan

I’m upgrading the exhaust fan in my bathroom and would like some advice from anyone with ventilation, glazing, or handyman experience.

Current setup:

• Existing fan: Fantech HCM-180N

• Installed through glass in a bathroom

• Glass cut-out is approx 220–225 mm diameter

What I want to install:

• New fan: Fantech HV-230AE (Stylvent 230)

• This fan normally needs a 260 mm cut-out

The issue:

I prefer not enlarge the glass hole as I believe this involves changing the entire window (costly) and
The HCM-180N hole is too small for the HV-230AE to mount normally.

Proposed solution:

I was told this is workable, and I’d like to confirm with people who have done similar:

Use two acrylic plates:

• One plate on the inside,

• One on the outside,

• Each approx 300 × 300 mm,

• Each with a 260 mm central cut-out sized for the HV-230AE.

The plates would be silicone-bonded to the glass (one each side), creating a new “virtual panel” with the correct cut-out size.
The HV-230AE (which clamps through the panel using threaded rods) would then mount through the plates, not through the glass.

This way:

• The existing 220 mm hole stays untouched,

• The fan mounts securely to the plates,

• The plates distribute the load across a wider glass area,

• No changes to the glass are required.

What I’m trying to confirm:

1. Is this a sound and safe way to install the HV-230AE using the smaller HCM-180N glass hole?

2. Any concerns about:

   • Long-term stability of silicone-bonded acrylic plates?

   • Vibration or noise transfer?

   • Airflow restriction from pulling air through the smaller 220 mm opening (the 230AE wants 260 mm)?

3. Anything I should do to reduce stress on the fan (e.g., bevel the inner hole edge, apply anti-corrosion spray, etc.)?

Fantech’s technical support said the fan “should work but with some increased pressure and reduced lifespan” due to the smaller opening, but is functionally acceptable.

Has anyone here done a similar plate-over-glass sizing trick?
Or installed a larger fan over a smaller hole using adapter plates?

Any practical tips would be appreciated before I order the parts.

 

Window glass type is seadraft

 

MitchellMc

Hi @Kingleviathan,

I think the manufacturer is always the best source for this type of installation advice, and it is good that you have already spoken with them. If they consider the setup workable, that at least confirms there is no technical reason the fan cannot run in this configuration. Their comment about increased pressure and reduced lifespan is also an important sign that the smaller opening will restrict the fan. That is the part that concerns me most. Because you are not enlarging the hole, the larger fan will still be drawing through a 220 millimetre opening. You may find that the airflow increase over the HCM-180N is minimal, or even that the HV-230AE is unable to perform anywhere near its rated capacity due to that restriction. The higher static pressure the motor has to work against is likely to be the main reason they've mentioned a reduced lifespan.

The silicone bonding idea is essentially a DIY workaround. It should physically hold, especially with large acrylic plates spreading the load across the glass, but it is not something many people would have practical experience with. That means you may not get much feedback from others who have done the same thing, simply because glass-mounted fans of this style are not that common these days. The long-term stability of silicone on acrylic and glass is generally good, but factors like vibration, heat, and bathroom moisture can influence how well it lasts over the years.

It is worth speaking to a glazier before committing to the plate idea. Increasing the size of an existing hole in glass is harder than cutting a fresh one, but some glaziers have methods for controlled enlargement using backer boards and staged cutting. If enlarging the hole is possible, even if it means replacing just the glass pane, it may give you a far more reliable installation and full fan performance.

Please let me know if you have any questions.

Mitchell