How to Install a Heat Pump Dryer and Close the Old Vent
Why this matters
A heat pump dryer is the one conversion appliance that removes a hole in the house rather than adding one. A conventional dryer, gas or electric, throws its moist exhaust air outdoors through a vent, and that vent is a 4 inch opening in the wall that leaks air every hour the dryer is off. A heat pump dryer recirculates its air in a closed loop and pulls the water out as liquid, so the vent is no longer needed.
This job has two predictable callbacks. The first is "it takes forever", from a customer nobody told about cycle times. The second is a water stain or a cold draft at the old vent opening a season later, because the duct was pulled and the hole was stuffed with insulation and caulked over. Both are prevented at the install.
The steps below follow one job: a laundry closet on a first-floor exterior wall, an electric dryer on a 240 volt, 30 amp circuit, a vent running 6 feet to a hood on the vinyl-sided back wall of a 1962 house. The customer wants a full-size 240 volt heat pump dryer.
How the machine works, in one paragraph
Air circulates from the drum across an evaporator coil, which chills it below its dew point so the moisture condenses into water, then across a condenser coil that reheats it before it returns to the drum. The refrigeration circuit is the same idea as a heat pump water heater or a dehumidifier. Because the air is warmed to a lower temperature than a resistance dryer reaches, drying takes longer and fabrics run cooler. The water collects in a reservoir the customer empties, or a small pump sends it out a drain hose.
Step 1: confirm the space before the customer buys
Measure the closet and check the model's installation instructions for three things: minimum clearances and ventilation for a closet install, maximum room temperature, and whether the unit is listed for stacking if the customer wants that.
Why: a ventless dryer still rejects heat into the room it sits in. A closet with a solid door and no louvers can climb toward the upper limit the instructions state, and the compressor protects itself by slowing the cycle down further. Skip it and you get the "takes forever" complaint with a cause no setting will fix.
On the example job, the closet has louvered bifold doors and the instructions allow closet installation with louvered doors. Pass.
Step 2: decide where the condensate goes
There are two choices, and the instructions decide which the model supports.
- Reservoir. A tank in the cabinet that the customer empties every load or two. No plumbing; forget it and the dryer stops mid-cycle.
- Drain hose. A pump in the unit sends water through a hose to a standpipe, a laundry sink or the washer's drain box. The instructions state a maximum drain height and hose length. Respect both: the pump is small.
Route the drain hose with an air gap at the receptor, meaning the end of the hose sits above the flood rim of the sink or inside the standpipe without being sealed into it. A hose pushed tight into a standpipe with a wet seal can siphon or take wastewater back toward the machine.
Why decide now: the drain point sets where the dryer sits and whether you need a second hose into the washer's standpipe. Skip it and the customer is emptying a tank every load in a house that had a standpipe 3 feet away.
On the example job, the washer's drain box is 34 inches above the floor, inside the drain height the instructions allow. The dryer's hose shares the standpipe through the manufacturer's drain kit with an open connection. Pass.
Step 3: confirm the electrical match
Read the nameplate and the instructions for voltage, the required circuit rating and the receptacle or cord configuration. Two common cases:
- 240 volt model on the existing 30 amp dryer circuit. Usually a straight swap onto the existing four-wire receptacle, if the instructions call for a 30 amp circuit. Check the existing receptacle is the four-wire type with a separate ground; an older three-wire receptacle is a separate conversation the sibling card on checking existing wiring covers.
- 120 volt model. Plugs into a standard receptacle and frees the 30 amp circuit. You cannot simply swap the 30 amp receptacle for a standard 15 or 20 amp one on the same breaker: NEC 210.21(B) as adopted requires the receptacle rating to match the branch circuit, so a 20 amp receptacle needs a 20 amp breaker. The freed 240 volt circuit is often worth keeping for a heat pump water heater or a future EV charger, so do not tear it out without asking.
Hazard at this step: testing or changing the receptacle means energized conductors. Turn off the breaker, lock or tag it, and prove the receptacle dead with a meter tested on a known live source before and after (live-dead-live, per NFPA 70E Article 120 (120.5 in the 2021 edition, renumbered in 2024), with work practices at 29 CFR 1910.333(b)(2)). If nobody on the crew is qualified for that electrical work, it goes to an electrician.
Skip it and a 120 volt dryer gets plugged into an adapter on a 30 amp circuit, which is an overcurrent device three times larger than the cord it protects.
On the example job, the new dryer is a 240 volt model calling for a 30 amp circuit, and the receptacle is four-wire. Straight swap.
Step 4: pull the old vent completely
Disconnect and remove the old dryer. Pull the duct out of the wall, all of it, back to the exterior hood. Do not leave a stub in the cavity.
Hazard at this step: old dryer ducts are lined with lint, which is highly combustible and full of fine dust. Bag it as it comes out, keep it away from any flame, wear eye protection and a filtering facepiece against the dust (worn voluntarily, which still comes with the information in 29 CFR 1910.134 Appendix D), and clean the cavity with a vacuum rather than blowing it out. A crushed or kinked duct packed solid with lint was a fire waiting; tell the customer what you found.
Why all of it: a duct stub in the wall is a pipe from the outside air into the wall cavity, which carries cold air, moisture and sometimes rodents. Skip it and you have sealed the inside of a hole that is still open to the weather behind the drywall.
On the example job, the 6 foot run comes out in two pieces of foil flex, the last foot crushed behind the dryer and about half full of lint. Bagged, photographed for the customer.
Step 5: close the exterior opening into the weather barrier
This is the step that gets skipped. Remove the exterior hood. You now have a hole through the siding, the sheathing and the weather-resistive barrier (WRB, the housewrap or felt layer behind the siding that sheds water that gets past the cladding).
The closure has to restore each layer in the right order:
- Sheathing. Cut a block of sheathing to fill the hole, backed by a cleat or blocking in the cavity so it is fastened to something solid.
- WRB. Lap a patch of compatible WRB or flashing tape over the sheathing patch so it sheds water shingle-fashion: the piece above laps over the piece below. Tape the top and sides, leave the bottom free to drain if your WRB manufacturer allows it. The detail and the lapping rules are in the sibling card How to Flash an Exterior Wall Penetration Into the WRB, which owns this.
- Cladding. Patch or replace the siding over it. On vinyl, that is usually a replacement panel or a split block cover; on wood or fiber cement, a patched piece painted to match.
Hazard at this step: in a pre-1978 house the siding paint may contain lead. Cutting, scraping or sanding painted surfaces disturbs lead dust, which is an inhalation and ingestion hazard to you and a contamination hazard to the occupants. EPA's Renovation, Repair and Painting rule (40 CFR 745 Subpart E) applies to paid work disturbing painted surfaces in pre-1978 housing above minor-repair thresholds the rule sets, and some states run their own program in its place. A hood replacement with a small patch may fall under the minor-repair threshold; a siding panel replacement may not. Follow lead-safe practices either way: wet methods, no dry sanding, plastic below, cleanup with a HEPA vacuum. On a first-floor wall this is usually a step stool job; anything higher gets a ladder set at about 4 to 1 and footed.
Why the layer order: caulking the siding alone sheds rain for a year or two until the caulk shrinks, and then water runs behind the siding, finds the unpatched hole in the WRB, and wets the sheathing and the framing below it. You see it as a stain on the laundry ceiling of the floor below, or as rot at the sill.
On the example job, the 1962 house has vinyl siding over the original painted wood clapboard. The tech tests the clapboard paint around the opening, gets a positive result, and handles the cut as lead-safe work. A sheathing patch, flashing tape lapped into the housewrap, and a replacement vinyl panel close it.
Step 6: seal and insulate the interior side
From inside, the hole through the drywall is patched like any other drywall patch. Before you close it, fill the cavity behind with insulation to match the wall and seal the drywall patch air-tight at its edges.
Why: the interior air seal is what stops warm indoor air reaching a cold sheathing patch and condensing on it. Skip it and you have built a cold spot with a draft on the inside of the wall.
On the example job, a 6 inch square drywall patch on the closet's back wall, insulation behind it, taped, mudded and primed.
Step 7: install, level and run the first cycle with the customer
Set the dryer, level it (the condensate path in many units depends on it), connect power and drain, and run a full cycle with a real load while you go over the controls with the customer.
Hazard at this step: you are energizing a new appliance. Confirm the cord or receptacle connection is complete and the breaker is the correct rating before you close the breaker, then stand to the side of the panel as you do it. Check the drain hose for leaks at the first pump-out.
Tell the customer three things:
- Cycles run longer. Often well over an hour for a full load, sometimes half again as long as their old dryer took. Lower drying temperature is the trade for the energy saved and the gentler treatment of fabric.
- Clean two filters. The lint filter in the door, every load, and a second filter or the condenser screen, as often as the instructions say. A clogged second filter is the most common reason a heat pump dryer gets slower over months.
On the example job, the first full load of towels takes about 1 hour 50 minutes against the customer's recollection of about 1 hour 10 minutes on the old dryer, roughly 1.6 times as long. The customer had read that it would be slower, and the tech showed her the eco and quick settings.
If the old dryer was gas
Two things change.
- The gas outlet gets capped and tested, per the sibling card How to Cap and Abandon a Gas Line Correctly, before anything else in this sequence. Shut the appliance valve, disconnect, cap, and leak test with a listed leak detection solution, never a flame. If you smell gas at any point, everyone leaves the house without touching switches, lights or phones, and the call to the utility goes from outside.
- The new dryer needs a circuit the old one did not have, unless the customer chose a 120 volt model and there is a receptacle in reach. A gas dryer usually sits next to a 120 volt receptacle for its motor and controls, which a 120 volt heat pump dryer might share only if the circuit meets the instructions' rating. A 240 volt model needs a new circuit, which means panel space and service capacity, which the sibling cards own.
If the gas dryer was the last gas appliance in the house, the close-out with the utility is the next step.
References
- IRC Section M1502 (clothes dryer exhaust), as adopted by your jurisdiction; listed condensing (ductless) dryers are installed per their listing and instructions rather than vented
- NEC 210.21(B) and Article 422, as adopted (receptacle ratings and appliance circuits); NFPA 70E Article 120 (120.5 in the 2021 edition, renumbered in 2024), and 29 CFR 1910.333(b)(2) for de-energized work
- EPA Renovation, Repair and Painting rule, 40 CFR 745 Subpart E, or your state's authorized program
- See related: How to Flash an Exterior Wall Penetration Into the WRB
- See related: How to Check That Existing Wiring Can Carry a New Circuit