How do you clean a sun tunnel?

The collector, on the roof

The one that matters, because dirt on it directly reduces the light delivered.

It sheds most dirt with rain, being domed or pitched. Under trees it accumulates leaf debris and sap and benefits from a wash once a year.

A water fed pole from the ground reaches most single storey collectors. On a two storey roof it is a job for a window cleaner rather than a ladder.

The diffuser, in the ceiling

Collects household dust on its upper face over years rather than months.

Most diffusers twist or clip out for cleaning. A wipe with a damp cloth on both faces, once every couple of years, is plenty. Check how yours comes out before you need to.

In a bathroom, steam carries soap and shampoo residue upward, so slightly more often.

The tube

Never. It is sealed at both ends, nothing gets into it, and the reflective surface stays as it was.

If there is condensation inside it, that is not a cleaning problem: the run needs insulating and the ceiling collar sealing.

If output drops over time

It is almost always the collector. Wash it before concluding anything is wrong with the installation.

The light kit

Where fitted, ask how the lamp is accessed. On most systems the diffuser comes down; on some it means loft access, which is worth knowing before the lamp fails rather than after.

Three parts, and only one needs regular attention

A sun tunnel has less to maintain than anything else we fit. There is no sash, no hinge, no actuator and no seal under daily thermal stress.

The roof dome. The part that matters. Clean it when the gutters are done, or twice a year under trees. Because the whole product depends on collecting light, a dirty dome costs output directly in a way a dirty window does not. Warm water and a soft brush, rinsed off. No abrasives on polycarbonate, which scratches easily and hazes.

On a pitched roof, rain does most of the work and an annual check is enough. On a low pitch or under a tree canopy, algae and leaf debris build up and it needs a hand more often.

The ceiling diffuser. Dust collects on its upper face over years. Most twist off, so it is a five minute job from a stepladder and it visibly improves the light. Wash it in warm soapy water, dry it properly and refit.

The tube itself. Do not attempt to clean it. It is a sealed system and there is nothing in it to clean. The mirrored surface is protected and reaching into it does more harm than good.

If there are insects in the diffuser

That is a seal to check rather than an insect problem. A sun tunnel is sealed at the roof and at the ceiling, so anything inside it got in through a gap.

Usually the fix is at the ceiling ring, which should be sealed airtight anyway to stop warm room air getting into the tube. It is worth resolving rather than ignoring, because the same gap that lets flies in lets moisture in.

If there is water at the diffuser

Far more often condensation than rain.

A metal tube passing through a cold loft is a cold surface. Warm moist air from the room getting into the tube condenses on it, and the water runs down and arrives at the diffuser looking exactly like a leak.

The cure is the two details that should have been done at installation: the tube insulated where it crosses unheated loft space, and the ceiling ring sealed airtight. Where the tunnel serves a bathroom, the extract fan needs to be working too, because a tunnel does not ventilate.

What eventually needs replacing

The dome. Polycarbonate yellows and hazes under ultraviolet over fifteen to twenty years, and it is a replaceable part rather than a reason to change the whole installation. A glass dome costs more initially and does not degrade, which on a south facing roof is worth the difference.

The mirrored tube has nothing to wear out. There is no reason a rigid tunnel installed properly should not still be working in thirty years with only the dome having been changed.