Installing a Zehnder ComfoAir 70

Vermont remodeler and home performance contractor Jim Bradley installs a compact, stand-alone wall-mounted Zehnder ComfoAir 70 energy-recovery ventilator on an airtight remodeled home.

On Site with Zehnder's New ComfoAir 70

New this summer to the United States, the Zehnder ComfoAir 70 is a decentralized energy-recovery ventilator (ERV) which provides tempered fresh air to 600 square feet of living space. This “spot ERV" drop-in doesn’t require any ductwork and has filtered supply-air and exhaust-air venting, as well as a washable ERV core (the enthalpy exchanger). The controls provide for four power levels with a maximum fan speed of 30 cfm. The rule of thumb for using the ComfoAir 70 is to ‘set it and forget it’, running the equipment continuously on mid-range speeds, but bumping the speed up to the maximum 30-cfm setting for large gatherings.

Using the Wall Cutout Template

Although the unit doesn’t need any complicated ductwork, it does require a fairly large hole through the wall. A cardboard layout template comes as part of the unit’s shipping box. Here, Matt Burstein, of Caleb Contracting in Cambridge, VT, placed the template in the middle of a stud bay and at a height so the controls will be easily accessible, about 3 feet above the finish floor. He then drilled a level pilot hole through the wall with a drill bit long enough to penetrate the full 11-inch-thick wall assembly (an 18-inch-long quarter-inch-diameter bit), using a torpedo level to keep the bit level.

Tracing the Template

The ComfoAir7 0 first became available last year in Europe, with most installations occurring in Switzerland and Austria. The instructions currently supplied with the appliance are in German, with measurements in metric units. Fortunately for Matt, he had a German friend who helped with the translation. Here, he cut out the 10.63-inch-diameter hole representing the unit’s wall installation pipe from the template, lined it up with the pilot hole, and then traced it on to the drywall.

Cutting the Exterior Opening

For the sake of precision, Matt decided to carefully cut into the wall one layer at a time, rather than rip through everything with a reciprocating saw. On the exterior, he centered the 10.63-inch-diameter cardboard template circle on the drill bit, and traced the circle onto the home’s WRB (left). He cut open the air barrier enough to be able to bore out the wall assembly’s material, and then traced the circle on the recently installed 3.5 inches of Roxul mineral-wool insulation (center). He cut the Roxul with an insulation knife (right), saving the resulting cylindrical cut-out to use as a plug in the wall pipe until final installation.

Boring Through the Superinsulated Wall

With the outer cavity's Roxul insulation removed, Matt cut through the existing 5/8-inch plywood sheathing with a recip saw (left). Also, he used the sawzall to roughly cut out the stud-bay’s Roxul insulation, careful not to rip into the interior Intello air barrier (center). The hole was cut at a 90-degree angle; there was no need to slope the 36-inch-long PVC wall installation pipe for drainage. He temporarily slipped the Zehnder-supplied wall pipe in to the hole in order to trace and cut the Intello from the inside (right).

Installing a Zehnder ComfoAir 70

To protect the Intello smart air and vapor barrier behind the drywall, Matt cut the wall installation pipe’s circle with a RotoZip, setting its bit half inch deep. He then used razor knife to finish the cut. With the circle complete, he cut a larger rectangle around the hole to allow for easier air sealing of the penetration later on.

Interior Circle Cut

With the drywall removed, Matt was able to trace the wall installation pipe, and then accurately cut the air barrier (the ‘white’ circle is daylight shining in from the exterior).

Through-Wall Pipe In Position

Here, the PVC wall pipe is in place, pushed into the interior.

Interior Air Barrier Sealing

The through-wall pipe is set flush with face of drywall, and then taped to the Intello air barrier membrane with Tescon Vana tape. As a precaution, Matt taped the drywall to the Intello at the location where the rectangular cut was made, just to be sure there would be no breach in the air barrier.

Exterior Air Barrier Sealing

On the exterior, the wall pipe was air-sealed to the outer air barrier with Tescon Vana tape. Later, double 5/4 spacer blocks made from Boral trim stock were used to build out the 11-inch-thick wall assembly to around 12.5 inches deep. (Because the fan for the unit is housed within this tube, Zehnder has a minimum tube length requirement of 12 inches.)

Transformer Junction Box

ComfoAir 70 units are typically hard-wired to power sources, rather than corded to an outlet. In this case, builder Jim Bradley requested a plug-in power option, which requires the installation of a junction box to house the unit’s transformer. Here, inserts a box into the wall.

Securing the Junction Box

Jason Marias of Locals Heating, Inc. (Underhill, Vermont) attaches the junction box to the wall with drywall anchors. As a cost saving, Zehnder is reportedly considering equipping future ComfoAir 70 units with preinstalled power cords allowing the units to be plugged into ordinary 120-volt receptacles, eliminating the need for custom work by an electrician.

Filters and Maintenance

Norbert Wesely of Zehnder America, Inc. explains maintenance recommendations for the ComfoAir 70. The unit has two removable filters, one for the supply side vent opening and one for the exhaust side. The paper filters should be inspected every 3 months (or more frequently in dusty locations), and replaced every 6 months (or more frequently as needed). A white LED on the unit blinks when the filters are due for inspection. The filters cost $29.50 per pair and can be ordered in bulk.

The Enthalpy Exchanger

The ERV core (enthalpy exchanger) transfers both heat and moisture. The vapor-permeable membrane allows moisture to migrate from the more humid to the less humid airstream: in the wintertime, when incoming air is cold and dry, the exchanger returns 60% of the home’s moisture from the outgoing stale air into the incoming airstream, helping to prevent excessive dryness. If indoor air is conditioned during the humid summer, the enthalpy exchanger transfers humidity as well as heat from the intake airstream to the exhaust airstream so that humid fresh air will not add to the latent cooling (dehumidification) load of the air conditioning system.

Attaching a Power Cord

Hvac technician Jason Marias drills a service hole in the ComfoAir 70 metal enclosure for a plug-in power cord. This unit was specially modified in the field to draw power by plugging in to a standard household receptacle. This soution may be offered as a standard option in future ComfoAir 70 units.

Laying Out for the Enclosure

Jason Marias and Zehnder America rep Norbert Wesely mark the wall for drywall anchors beofre mounting the enclosure to the wall.

Wiring Up the Transformer

The power transformer packaged with the ComfoAir 70 converts household current to 24 current to power the unit's DC motors. Here, hvac technician Jason Marias and Zehnder America rep Norbert Wesely solder leads onto the transformer and place the component into the electrical box in the wall.

Mounting the Enclosure

Wesely and Marias attach the ComfoAir 70 enclosure's rear panel to the house wall using drywall anchors. Be careful not to over-drive the anchors, warns Wesely, or the enclosure's front cover may be hard to remove and reattach for maintenance.

Final Wiring

With the unit's air shaft inserted into its through-wall protective sleeve, Norbert Wesely finishes making the required electrical connection.

Internal Electronics

A close view of the ComfoAir 70's control circuitry.

Final Insertion

With the wiring setup completed, Norbert Wesely slides the polypropylene-insulated air tube (which also contains the unit's fan) into the through-wall pipe, and sets the interior portion of the device into its metal housing. The fit is snug.

Excess Pipe

The protective through-wall pipe and the insulated air duct for the ComfoAir 70 are long enough to extend through about a two-foot-thick wall. For this thinner wall section, the extra pipe has to be cut off. But at least 12.5 inches of pipe has to be preserved, because it is occupied by the unit's fan. Here, the superinsulated wall has been packed out with a block of 5/4 material to add the required wall thickness.

Trimming the Pipe

Jason Marias trims the excess pipe flush to the exterior trim piece using an oscillating multi-tool.

Exterior Louvers

Norbert Wesely screws the ComfoAir's exterior vent grille cover onto the end of the air intake and exhaust pipe.

On the Wall

A view of the appliance after installation.

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