Where termite heat treatment goes wrong, and when to use it
Heat treatment for termites killed only 36 to 44 percent of drywood termites near a concrete foundation wall in a University of California trial.
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Termite heat treatment kills drywood termites living in a home’s wood, and only in the boards and beams that heat through to the core. It goes wrong in wood that won’t heat through, against termites nesting in the soil, and after the job ends, because heat leaves no protection behind.
The University of California sets the target at a core temperature of at least 120°F, held for at least 33 minutes, in all of the wood in the structure (drywood termite guidelines). To get there, crews cover the house with tarps and blow in hot air until the inside reaches 140° to 150°F (California’s termite Q&A). How long that takes depends on the building’s construction and the weather, and the method may not be practical for a structure that cannot be heated evenly.
Heat only fits termites that live in the wood
If the heat quote came after someone found mud tubes on a foundation wall, ask why heat was offered at all. Subterranean termites nest in soil and reach wood through earthen shelter tubes (UC IPM quick tips). They need a separate treatment that puts a barrier between the building and their nest in the ground (California pest regulators). Heating the house does not treat the soil where that colony lives.
Drywood termites are the target. They nest inside wood with no need for soil contact. They push out hard pellets with six sides, a shape that marks them as drywood termites (UC IPM). The pellets measure about 1 to 2 mm, smaller than a rice grain, and tend to collect in small piles under the infested wood (Florida drywood termite guide). The differences between subterranean and drywood termites go well beyond this one decision.
Dampwood termites also live in wood, but they need wet wood. The fix for them is correcting the moisture problem and replacing the damaged pieces (UC IPM).
What happens on treatment day?
Hours, rather than days, is the usual time out of the house (UC IPM). Large beams set the pace: raising the core of a big infested timber to a lethal temperature can take many hours or even days, depending on how much wood is being heated.
The crew covers the house or the treated rooms with tarps or thermal blankets and seals roof and wall vents. Heaters and fans then run while probes report temperatures from inside the wood. That setup is described in a Honolulu field study of drywood termite heat jobs. Before treatment day, these come out or get protected:
- Pets and plants (California’s guidance)
- Aerosol cans, fire extinguishers and adhesives (Honolulu study’s prep notes)
- Plastics such as electrical outlet covers, and cable wiring (UC IPM)
- Food crumbs and other debris, vacuumed up, since debris can insulate a surface from the heat (same study)
Possible roof damage, if the crew walks on the roof, is one of the drawbacks listed for heat (UC IPM).
Safety: Aerosol cans and fire extinguishers are pressurized, and both leave the treatment zone along with adhesives before the heaters start. The heaters and probes belong to the licensed operator. Do-it-yourself drywood treatment is not recommended (UC IPM), and no extension source gives homeowners a heat method to try.
Tenting with gas has a different prep list, with food bagging and a gas shut-off, set out in preparing for termite fumigation.
Cold spots where termites survive the heat
University of California researchers heated a test house to 134–146°F for 140 minutes. In test blocks set beside its concrete foundation wall, only 36 to 44 percent of drywood termites died (UC ANR report on the trial). Termites can survive in hard-to-heat spots such as wood against a foundation wall. Blocks near that wall treated with wintergreen oil reached more than 90 percent kill, a result from the research trial.
The weak points match the UC IPM guidelines: wood on concrete or tile, large beams whose cores heat slowly, and homes with many layers of wall covering. In those homes, newer heaters have not yet been shown to rid large structures of every infestation. Termites also move. Drywood termites tend to avoid high temperatures and may retreat to cooler wood, where they survive if lethal temperatures never arrive (condo heat study).
What the Honolulu condo study found
Five Honolulu condominiums with West Indian drywood termites in kitchen cabinets were split between two methods. Three received a standard commercial heat job. In the other two, the crew drilled 4-inch holes into the toe-kick voids under the cabinets, ducted hot air through them, and placed probes inside the voids. Six months later, one of the three standard units still had termites and pellets; neither improved unit did (Tay and James, Insects). Five units is a small sample, and the findings apply to condos with wood cabinetry and furniture.
| Where heat struggles | Why it stays cooler | What to ask the operator |
|---|---|---|
| Wood resting on a slab or foundation | Concrete acts as a heat sink | Will a probe sit in wood that touches the concrete? |
| Wood under or against tile | Tile acts as a heat sink | Where do the probes go in tiled rooms? |
| Cabinet toe-kick voids | Enclosed voids heat slowly | Will hot air be ducted into the voids? |
| Large structural beams | The core can take many hours or days | How will you confirm the beam’s core temperature? |
Sources: UC IPM Pest Note 7440; UC ANR trial report; Honolulu condo study.
The University of California standard is not the only one in use. Florida research reached complete kill when the wood’s interior held about 130°F for one hour, as reported in the Honolulu paper’s review. Ask which target your operator works to, and why.
Does heat treatment stop termites from coming back?
Heat leaves nothing behind in the wood. Like fumigation, it has no residual effect, and longer protection comes from preventive treatments applied to the treated areas afterward (UC IPM).
Soil treatments and bait systems do not protect a structure from drywood termites (Florida drywood termite guide). Termite protection contracts in Florida usually cover one termite type, with a separate contract for the other, so check which species your warranty names. The questions to ask before signing a termite bond cover the rest of the fine print.
To judge whether the job worked, clean up the pellets below a kickout hole and look again a few days later. New pellets point to activity, though building vibration can shake a few old ones loose. Pellets alone cannot show whether an infestation is still active (UC IPM). The Honolulu researchers made their follow-up inspection at six months.
Heat or fumigation for a drywood infestation
California’s pest board treats fumigation and heating the entire house as the only choices that reach termites throughout a structure, since spot methods leave hidden infestations elsewhere (board’s consumer brochure).
| Factor | Heat | Fumigation |
|---|---|---|
| Chemicals | None | Sulfuryl fluoride gas |
| Time out of the house | Hours | Six hours to one week |
| Results in the field | Vary with house size and wall coverings | High when gas levels are monitored |
| Protection afterward | None | None |
| Treating part of a building | Possible, such as one condo unit | Must cover the whole structure |
| Damage risks | Heat-sensitive items; the roof, if walked on | The roof, from tarps or walking; gas pilots must be put out |
Sources: UC IPM Pest Note 7440; board’s consumer brochure for time out during fumigation; Tay and James, Insects for fumigation covering the whole structure.
Heat generally costs more than chemical treatment, and the drilled-void method in Honolulu took more labor than a standard heat job (field study’s cost notes). Longer heating raises the price, and heating time grows with the size of the treated area and the materials in it. The termite treatment cost comparison puts heat beside the other methods.
Spot heat brings only the targeted timbers up to the lethal wood temperature. A company promising whole-house results from spot methods is engaging in false advertising and can be reported to the board (same brochure). Other localized methods, including orange oil injected into a known gallery, share that limit: they reach only the wood someone found.
For renters: Heat can be run in a single apartment or condo unit (UC IPM), while fumigation has to cover the whole structure (condo heat study). Who arranges and pays for treatment depends on the lease and state law, which termites in a rental and who pays walks through.
Questions to put to a heat operator before you sign
Get the species identified in writing first. Florida’s consumer guide asks for a positive identification by an experienced pest control operator when drywood termites are suspected, and at least three opinions and cost estimates from licensed companies (drywood guidance from FDACS). With that in hand, ask the licensed structural pest control operator who quotes the heat job:
- Is this a whole-structure job, or a spot treatment of specific boards?
- Where will the core probes go, and will one sit in wood touching the slab?
- What core temperature will you hold, and for how long?
- Will hot air be ducted into toe-kick voids and other enclosed spaces?
- Which items do I remove, and will anyone walk on the roof?
- What does the written guarantee cover, and which termite type does it name?
- Is an annual inspection included?
Getting at least three inspection reports and reading the guarantee closely are part of the same University of California guidance.
Check the license before you sign. California licenses can be verified online with the state board (California licensing board). In Florida, the agriculture department’s Bureau of Licensing and Enforcement takes questions about a company at 850-617-7997 (FDACS guide). In other states, ask for the license number and look it up with the agency that issued it; that agency decides whether a license is current.
Termites damage wood slowly, so a few extra days spent deciding usually adds little damage. Firms that press for an on-the-spot signature with specials or scare tactics are best avoided (California licensing board). Book the inspections first, and compare heat quotes only after the species and your home’s cold spots are on paper.
