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Hardwood Floor Acclimation: The 5 to 7 Days, the Moisture Meter, the Numbers That Have to Match Before a Board Goes Down, and Why Installers Skip It
Flooring & Tile
Acclimating Hardwood: It Is Not “Leave the Boxes in the Garage for a Week,” and the Meter Is the Only Thing That Tells You When It Is Done
Acclimation is the part of a hardwood job that nobody sees and nobody charges for, which is exactly why it gets skipped. The idea is simple: the boards arrive at one moisture content, the house and the subfloor are at another, and if they go down before they agree, the floor spends its first season sorting out the difference by gapping or cupping. Five to seven days in the room usually does it. But the days are not the test; the meter is. Here is what the numbers have to be, how a good installer checks them, and why the cheap quote does not include the wait.
What acclimation is and is not
Wood flooring leaves the mill at 6 to 9% moisture content and goes into a warehouse, a truck and a store, picking up or losing moisture the whole way. The subfloor in your house has been sitting at the house’s humidity for months and is at whatever that works out to. The floor is “acclimated” when the boards and the subfloor are within a few points of each other, and both are inside the range the house will live at. That takes however long it takes: three days in July for boards that came from a warehouse in the same town, two weeks in January for a pallet that sat in an unheated truck.
It is not: a week in the garage (the garage is not the house), a week in a house with no heat on yet (the furnace is not running, so the house is not at living conditions), or a week in unopened, plastic-wrapped boxes (the wrap keeps the air out). Boxes get opened or cross-stacked with spacers, in the rooms where the floor will go, with the heating or cooling running the way it will when you live there. For a new house that means the HVAC has been on for a week or more and the drywall and paint are dry, which is also why hardwood is one of the last trades in. The installation order page covers that sequence.
The numbers
| What | Limit | How it is checked |
|---|---|---|
| Room conditions | 35 to 55% RH, 15 to 27 C | A hygrometer in the room for the whole acclimation, and for the life of the floor. |
| Flooring vs wood subfloor | Within 4 points of each other; within 2 for plank over 3 in. wide | Pin meter on several boards from several boxes and on the plywood in several spots, written down with the date. |
| Wood subfloor itself | Under 12% MC | Pin meter. New plywood that got rained on during framing is often 16 to 20% and needs weeks of heat. |
| Concrete slab, for glue-down or floating | Under 75% RH by in-situ probe (ASTM F2170), or under 3 lb per 1,000 sq ft per 24 hr by calcium chloride (ASTM F1869) | Probes drilled into the slab 72 hours before reading, or the dish test under a sealed dome. A $30 pinless meter on the slab surface is a screening tool, not a test. |
| Subfloor flatness | 3/16 in. in 10 ft | A straightedge or a string line; the humps get sanded or ground, the dips filled. Levelling costs. |
| Time | 5 to 7 days typical | Until the readings above are met. The days are a guide, the meter is the rule. |
A good installer writes the readings on the box or on the invoice. If a floor fails later, those numbers are the difference between his problem and yours. Our subfloor checklist has the photographs to take alongside them.
The meter
A pin meter pushes two needles into the wood and reads electrical resistance, which tracks moisture content; set it to the species and it reads to about a point. A pinless meter reads through the surface by capacitance and does not mark the board, which makes it the one to use on finished flooring and on a slab as a first look. Either one costs $40 to $300 and every installer should own one and use it in front of you. Mine lives in the truck door and comes out before the first box is opened, on the subfloor at the exterior walls, by the patio door, near the kitchen sink, and in the middle of the room, because those four spots are never the same number.
On a slab, the in-situ probe is the one that counts for a glue-down or a manufacturer’s warranty. The installer drills three holes per 1,000 sq ft, drops the sleeves in, lets them sit 72 hours, and reads the humidity inside the concrete itself. It is the only test that tells you what the slab will do to the adhesive next February. The concrete moisture page goes through the F2170 and calcium chloride tests in detail; they are the same for wood.
Why installers skip it
Because it is unpaid time. A crew that has two days of nailing booked wants to arrive Monday, nail, and be on the next job Wednesday. Acclimation means somebody has to bring the material a week early, open the boxes, come back with the meter, and maybe tell you the floor is not ready, which is a conversation nobody enjoys. On a production house the schedule is set by the site super, the wood comes off the truck Monday morning, and the floor is down by Tuesday night. Sometimes that is fine. Sometimes it is a Tarion claim.
The other reason is that the material is often close enough and the installer has learned he gets away with it. He does, until the pallet that sat in a cold trailer, or the slab that was poured in October and is still giving off water in March. The hiring page has the question to ask: “What readings do you take before you start, and will you write them on the invoice?” The pause before the answer tells you most of what you need.
What skipping it costs
Take the 900 sq ft main floor from the solid hardwood cost page: $12,920 before HST for mid-grade oak nailed, with trim and delivery. Say the boards went down the day they arrived, 4 points wetter than the subfloor, in a tight new house. By February the floor has gapped so badly the client can see the subfloor paper, and by the next August it has swelled back and crushed the edges of half the boards. The fix is a new floor: remove the old one at $2.00 a square foot, $1,800, a $450 bin, and the $12,920 again. $15,170 to redo a job that a week of waiting would have saved.
Who pays depends on the paperwork. An installer with no meter readings and a seven-day gap between delivery and installation that the invoice shows was one day has a hard time. An installer who wrote down the readings and installed within spec hands the problem to the humidity in your house, and he is usually right to. Warranty problems covers how those claims actually go.
Where homeowners go wrong
- Storing the wood in the garage or the basement. Neither is the room. The garage is 2 C in March; the basement is 65% RH in July. Put it where it is going.
- Acclimating in a house with the heat off. The boards settle to a vacant house and then the furnace comes on. Living conditions means living conditions.
- Trusting the days and not the meter. Seven days is a guess that is usually right. Thirty seconds with a pin meter is a fact.
- Letting the slab skip the probe test because “it has been there ten years”. Age is not dryness. A slab on wet ground with no poly under it reads 90% RH forever. Basement flooring.
- Taking delivery before the painters are done. Fresh paint and primer put gallons of water into the air. The wood reads it.
Questions people ask
How long should hardwood flooring acclimate before installation?
Five to seven days in the rooms where it is going, at living conditions, with the boxes opened, is the usual answer, and the real answer is until a moisture meter shows the boards within 4 points of the subfloor (2 for wide plank). Some products from local warehouses are ready in three days; a cold pallet in January can take two weeks.
Does engineered hardwood need to acclimate?
Yes, though it is more forgiving. The Canadian mills call for 48 to 72 hours at minimum and the same humidity window, 35 to 55%. Over a slab, the slab test matters more than the board.
What moisture content should hardwood be before installing?
Typically 6 to 9% for solid flooring in a heated Ontario house, and within 4 points of the subfloor, which should itself be under 12%. The exact target depends on the humidity the house will live at: a house kept at 35 to 55% RH settles wood at 7 to 10%.
Can hardwood be installed in winter?
Yes, and plenty is. The house needs the heat on and a humidifier running so the air is not at 20%, the wood needs a longer acclimation because it arrived cold, and the installer needs to expect that the floor will be at its narrowest when he lays it and leave the expansion gap accordingly.
Who is responsible if the floor was not acclimated?
The installer, if the floor fails from moisture in the first year and he cannot show readings and a reasonable acclimation period. The homeowner, if the readings were taken and in spec and the house was then run outside the 35 to 55% window. Write it into the contract. The contract checklist.
Build the week into the schedule and the price
The flooring cost calculator prices the floor; the acclimation is free, which is the best price on this whole site. If your quote has the delivery and the installation on the same day, the $99 review will flag that before it becomes your floor.
Sources and further reading
- National Wood Flooring Association: the installation guidelines every hardwood warranty points to: subfloor flatness, moisture limits, acclimation, fastening schedules and the radiant-heat chapter.
- Mirage Hardwood Floors: Quebec-made solid and engineered hardwood; their installation guides give the moisture, acclimation and radiant limits in plain numbers.
- Torlys: Canadian maker of engineered, vinyl and laminate floors; the installation and radiant-heat instructions are a good example of what the sheet in the box says.
