Thursday, July 17, 2014


Frequently, I deal with issues related to condensation in central vacuum piping. Signs of condensation issues include:

-Low suction from upstairs inlets

-Moisture present in central vacuum unit

-Liquid or “brown goo” dripping out of central vacuum inlets

-A distinctive, nasty mildew smell

Condensation issues occur when the vacuum pipe transitions from a heated living space to an unheated attic. During the winter, warm house air contacts cold attic air, with condensation forming on the warm side (inside the pipe). Though many central vacuum installations involve running piping through unheated areas, condensation only becomes an issue in some cases:

-The difference between the living space temperature and attic temperature must be significant…aggravating factors include running the pipe above the attic floor and insulation, an unusually cold attic, and/or an unusually warm living space

-Dripping from the inlet only occurs when the attic tubing slopes down toward the inlet, causing the condensation to drain to the lowest point

Obviously, this is a problem you want to avoid dealing with. When installing vacuum systems in new construction, piping should run down to the machine if at all possible, rather than up-over-down. Many new construction central vacuum installations (especially those performed by firms whose primary work is electrical or low voltage wiring) have the second floor inlets running up into the attic, then connected together into one pipe that runs down to the machine (sometimes in an exterior wall!). In 99% of new construction work, it is possible to bring the piping down from the upper floor inlets.

Retrofitting vacuum systems to existing homes requires a different approach, making use of the access that’s available. Sometimes, upper levels are small enough to allow full coverage from just one inlet. In this case, try to locate the inlet where piping can run straight down. Make use of stacked walls, stacked closets, cold air returns, laundry chutes, etc. Time spent exploring the way a home is constructed will definitely pay off.

If servicing the second floor requires piping to run through the attic, keep the piping as close to the heated space as possible, and build up insulation in a mound around the tubing. Make a “trap” at the top of inlet risers so that, if condensation does ever form, it doesn’t reach the inlet:


Note: Let’s all take a moment and be thankful that my central vacuum installation skills are better than my MS Paint skills.

Of course, never install a tee or wye branch at less than horizontal, which allows dirt to fall down into inlet risers. Also, wye fittings are always preferable to tee fittings (see my blog post on the differences here).

Often, condensation problems with existing systems aren’t addressed until they’ve become bad enough to cause a loss of suction from buildup in the piping. If the blockage is not severe, usually strong reverse flow (from a high-pressure central vacuum or special unclogging unit) will remove it through the affected inlet.

Even if the blockage can be removed this way, the piping should be visually inspected. Plan to replace and reroute piping if any of the following conditions exist:

-Flow is not proper (tight turns, drop-out tees/wyes, three-way tees, etc.)

-Piping slopes down to inlet

-Piping runs elevated instead of tight to joists

-Buildup is severe (indicated by a measurable difference in working vacuum between upstairs and downstairs inlets, even after main clog is removed)

For lighter buildup, sometimes “TornadoPower” central vacuum maintenance cloths will improve the flow, though they may also turn a partial clog into a full clog and require manual removal.

I have had some success with vacuuming absorbent, slightly abrasive materials through lines with buildup issues. Dry rice is often recommended, though a material like Oil-Dri, non-clumping cat litter, or even silica gel crystals might work well. The more the better.

After piping repairs have been made, insulation is critical to preventing the problem from reoccurring. The insulation should be a barrier between the piping and the attic temperature, NOT the living space temperature. In other words, the goal is for the pipe to assume the temperature of the heated living space as much as possible.

The approach shown below right, as if a “pipe wrap” type of insulation were applied over elevated attic piping, is not effective. Below left is better, though care should be taken to reduce the amount of insulation between the pipe and the heated space, and increase the amount separating the pipe from the unheated attic.


If the tubing runs parallel to joists, try to install it next to the drywall ceiling, then cover with insulation. If (as is more common) the tubing is running perpendicular to the joists, then fiberglass bat insulation can “inchworm” over the pipe, allowing the pipe to sit in a pocket of warmer air.

It can be difficult to eliminate the odors related to condensation issues right away. Odors will diminish over time once new condensation and debris buildup is prevented from forming. Be sure all inlet covers seal tightly when not in use, and exhaust the power unit outside to eliminate odor at the unit location. Fragrances can be used in the central vacuum piping and power unit to mask the odor until it dissipates.

We offer free estimates to homeowners in the Chicagoland area who may be experiencing the above issues with their central vacuum system. Contact us at, or call 630-608-0175 for more information.

1 comment:

  1. This was a very useful article. I've been battling the condensation for weeks now. I'm going to take the articles advice and see if the pipes are running elevated. Thanks for the helpful tips.