Roundup · Freeze protection
A crawl space does not need to be warm. It needs to not reach 32°F, unattended, for four months — which rules out most of the category on specs nobody normally reads.
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Freeze protection needs a thermostat with a published low set-point, a tolerance for damp, and a fan that will run unwatched for months. Hold the space at about 40–45°F rather than 33°F, because pipes in unheated cavities freeze before the room air does. Most heaters publish none of these specs.
Every other roundup on this site is about comfort: getting a space you occupy to a temperature you enjoy, for the hours you are in it. Freeze protection inverts all three variables. Nobody is in the space, the target temperature is one you would find unpleasant, and the duration is the entire winter. The specs that decide a comfort heater — oscillation, noise, how fast it warms a room — are irrelevant, and the specs that decide this one barely appear in the marketing.
That last point matters for the picks below. One unit here is sold with a thermostat reaching 32°F and three bottom out at 37–41°F, and on the reasoning above that difference is close to meaningless — you should not be setting 33°F anyway. What separates the picks is the damp rating, the fan, and whether you can get the thing off the floor.
This is the one number we genuinely cannot give you, and it is worth being explicit about why. A freeze-protection heater cycles — it runs until the space hits the set-point, stops, and restarts when it drifts down. The fraction of the time it spends running depends on the outdoor temperature, the insulation, the air sealing and the volume of the space, none of which we can see. Anyone quoting you a monthly figure for a crawl space heater is guessing.
What we can give you is the ceiling: the cost if it never cycles off at all. Everything below that is a duty cycle you will have to measure yourself.
| Wattage | Per hour | 4 h | 8 h | 24 h |
|---|---|---|---|---|
| 600 W | 11.0¢ | $0.44 | $0.88 | $2.64 |
| 900 W | 16.5¢ | $0.66 | $1.32 | $3.96 |
| 1,500 W | 27.5¢ | $1.10 | $2.20 | $6.60 |
Computed at 18.34¢/kWh — the U.S. residential average for June 2026 (EIA, Electric Power Monthly, Table 5.6.A, released August 26, 2026). Your rate is on your own bill; substitute it and the arithmetic still holds. Figures assume full output for the whole period.
Run flat out around the clock, 1,500 W is roughly $6.60 a day, and that is the worst case rather than the expectation — a reasonably sealed crawl space holding 42°F in a mild week may run a small fraction of that. This is also the strongest argument for a heater with a published low wattage setting: one of the picks below idles at 600 W, which caps the worst case at about $2.64 a day while still being more heat than a well-sealed cavity usually needs.
The rate behind every figure on this site
18.34¢per kilowatt-hour
U.S. residential average for June 2026. EIA, Electric Power Monthly, Table 5.6.A, released August 26, 2026.
This is the most recent month EIA has published. Residential rates move seasonally and vary enormously by state — from roughly a dime per kilowatt-hour in parts of the South to more than 40¢ in Hawaii — so treat it as a national reference point, not as your rate.
If you have a perfectly good heater with a useless dial thermostat, you do not necessarily need a new heater. A freeze-protection thermostat outlet is a plug-in module that sits between the wall and the heater and closes the circuit at a fixed low temperature — the common ones switch on around 35–38°F and off around 45–50°F. You set the heater's own dial to a middling output and leave it; the outlet decides when it runs.
We have not made this a pick and there are no buy links for it, because it is a thermostat rather than a space heater and this site covers space heaters. But it is the honest answer for a lot of people arriving at this page, it costs a fraction of a heater, and leaving it out to keep the page tidy would be the kind of omission we would criticize elsewhere. Search the category name and read the switch-on temperature before buying; they vary.
A crawl space is as far outside the heated envelope as a space gets, so the sizing rule takes the 1.5 multiplier — 15 W per square foot rather than 10. The table below is the demand for a space you are trying to make comfortable, which is not what you are doing here, so treat it as an upper bound: holding 42°F rather than 68°F is a much smaller job than these figures suggest.
| Room size | Watts needed | BTU/h | Plug-in heaters |
|---|---|---|---|
| 200 sq ft | 3,000 W | 10,236 | 2 (different circuits) |
| 400 sq ft | 6,000 W | 20,473 | 4 (different circuits) |
| 600 sq ft | 9,000 W | 30,709 | 6 (different circuits) |
| 900 sq ft | 13,500 W | 46,064 | 9 (different circuits) |
Computed as square feet x 10 W x insulation factor x (ceiling / 8 ft), for an unheated space (garage, unfinished basement) — 15 W/sq ft, 8 ft ceiling. Heater count assumes the 1,500 W plug-in ceiling.
In practice the useful reading is the other direction. A 1,500 W plug-in unit is comfort-rated for about 100 sq ft of unheated space, and will hold a considerably larger one just above freezing. A 600 sq ft crawl space would need 9,000 W to be warm and nothing like that to stay unfrozen — which is why a single 120 V unit is a reasonable answer here when it would be hopeless in a garage you actually want warm.
Ranked for fit, not for hype. Coverage and current draw are computed from each unit’s published wattage. Tap a row for the full write-up, or go straight to the listing.
| # | Product | Best for | Covers | Draw | Price |
|---|---|---|---|---|---|
| 1 |  Dr. Infrared DR-218The only heater in our registry whose maker publishes a moisture rating, and the only one whose thermostat is sold as reaching 32°F — which is the entire job when you are protecting a crawl space rather than warming a room. | Holding an unheated space above freezing | 150 sq ft | 12.5 A | $100.74 · Check on Amazon |
| 2 |  Pelonis PSHO07JR4AGBThe digital Pelonis: every one of its three wattages is published, the thermostat sets to the degree, and it is the only oil-filled radiator here with a child lock. | A radiator with a child lock and a real set-point | 150 sq ft | 12.5 A | $109.99 · Check on Amazon |
| 3 |  Dreo WH517SThe cheapest genuinely verifiable smart heater here, and the only one in the category that publishes a noise figure — 28 dB on its lowest setting. | A published decibel figure on a smart heater | 150 sq ft | 12.5 A | $84.53 · Check on Amazon−15% |
| 4 |  Dr. Infrared DR-966The pick if a published listing mark matters to you, which on a hardwired ceiling appliance it reasonably might — but read the brand name as a brand name, because this model is not infrared. | The only one with a real safety listing | 600 sq ft | 25.0 A | $175.70 · Check on Amazon |
Coverage computed at 10 W/sq ft, average insulation, 8 ft ceiling. Draw computed as watts ÷ volts. Neither figure is a manufacturer claim.
Top pick · Holding an unheated space above freezing
The only heater in our registry whose maker publishes a moisture rating, and the only one whose thermostat is sold as reaching 32°F — which is the entire job when you are protecting a crawl space rather than warming a room.
| Published specification | |
|---|---|
| Rated power | 1,500 W at 120 V, NEMA 5-15 plug (iLiving) |
| Current draw | 12.5 A (1,500 ÷ 120) — our figure. Retail listings print “15 A”, which is the circuit and plug rating, not the draw |
| Thermostat | 32–104°F per the retail listings. iLiving publishes “adjustable thermostat control” with a “precision temperature sensor” but NOT the range — verify before relying on it unattended |
| Moisture rating | “IPX4 structure; protected against water splashing” (iLiving) |
| Motor | “Totally enclosed, thermally protected and heavy duty ball bearing motor”, “permanently lubricated for life” (iLiving) |
| Maker's coverage claim | 150 sq ft (retail listings) — exactly 1,500 W at 10 W per square foot |
| Output | 5,118 BTU/h — our figure from the rated wattage; listings round it to 5,200 |
| Element type | Not published by iLiving or any retailer |
| Weight | 13 lb (iLiving) |
| Warranty | One year (retail listings) |
| Larger variant | A DR-218-3000W exists at 240 V on a NEMA 6-20 plug — a different circuit, not a bigger version of this one |
| Heat type | Fan-forced |
| Maker’s coverage claim | 150 sq ft |
| Safety listing | Retail listings (Tractor Supply, Zoro, HomElectrical) publish cUL/UL Listed. iLiving's own product page does not name the mark, so check the rating plate. |
Who it is for
A crawl space, well house, pump house, greenhouse or detached garage you need held above freezing through the winter, on a standard outlet, where damp is a realistic risk.
What it is not for
Protecting pipes specifically — that is heat cable's job, not a space heater's, and it is outside what this site covers. Also not a room heater: 1,500 W and a 32°F setpoint is a freeze-protection tool, not a comfort one.
Sources for this entry
2 · A radiator with a child lock and a real set-point
The digital Pelonis: every one of its three wattages is published, the thermostat sets to the degree, and it is the only oil-filled radiator here with a child lock.
| Published specification | |
|---|---|
| Rated power | 600 W / 900 W / 1,500 W at 120 V (all three published) |
| Thermostat | 41–95°F in 1°F increments |
| Modes | ECO, Sleep and Memory |
| Timer | 24 hours |
| Controls | Touch panel plus remote |
| Construction | 108 “Volcano” thermal vents |
| Maker's noise claim | “<5 dB” — fanless; see the note on the comparison page |
| Safety | Tip-over protection, overheat auto shut-off, child lock, V0 flame-retardant housing |
| Heat type | Oil-filled |
| Maker’s coverage claim | 255 sq ft |
| Safety listing | Pelonis publishes a V0 flame-retardant housing, tip-over protection, overheat auto shut-off and a child lock, but does not name a UL or ETL mark. Check the rating plate. |
Who it is for
A bedroom, nursery or study where silence is the requirement, someone else in the house should not be able to change the settings, and you want to set an actual temperature and a shut-off time.
What it is not for
Fast heat, or a room much over 150 sq ft on our arithmetic. It is a radiator: it warms slowly and steadily, and that is the design rather than a fault.
Sources for this entry
3 · A published decibel figure on a smart heater
The cheapest genuinely verifiable smart heater here, and the only one in the category that publishes a noise figure — 28 dB on its lowest setting.
| Published specification | |
|---|---|
| Rated power | 1,500 W at 120 V (Dreo publishes “1500W Max” and 3 heat settings, not their wattages) |
| Thermostat | 41–95°F, 1°F increments (Dreo's published figure) |
| Smart control | Wi-Fi, Dreo app, Alexa and Google Home |
| Noise | 28 dB, published in the listing (lowest setting) |
| Ingress rating | IP24, published in the listing |
| Other modes | ECO mode, fan-only |
| Mounting | Wall-mounted — not a portable unit |
| Heat type | Ceramic (PTC) |
| Maker’s coverage claim | None published — the coverage figure above is ours |
| Safety listing | Dreo's product page does not publish a UL or ETL mark for this model. The listing does publish an IP24 ingress rating, which is a different thing and is not a safety listing. |
Who it is for
A bedroom, small office or bathroom wall where quiet matters and you want app control and a schedule at the lowest price that is still verifiable.
What it is not for
Anywhere you need to move the heater, and not a room where you need a published safety listing before you buy — check the rating plate first.
4 · The only one with a real safety listing
The pick if a published listing mark matters to you, which on a hardwired ceiling appliance it reasonably might — but read the brand name as a brand name, because this model is not infrared.
| Published specification | |
|---|---|
| Rated power | 6,000 W high / 3,000 W low at 240 V, single phase |
| Current draw | 25.0 A high, 12.5 A low — our figures (6,000 ÷ 240). The maker publishes no amperage |
| Minimum circuit ampacity | 31.3 A — 125% of the draw under the NEC continuous-load rule, which needs a 35 A breaker |
| Recommended wire | 8 AWG copper, per the manufacturer |
| Output | 20,473 BTU/h at 6,000 W — our figure; the maker publishes no BTU rating |
| Maker's coverage claim | 600 sq ft |
| Heating element | Spiral steel metal sheath behind an 8 in fan, with 5 adjustable louvers |
| Thermostat | Built-in adjustable, 37–104°F |
| Dimensions | 14.5 in high × 13 in wide × 14.5 in deep |
| Warranty | One-year limited component warranty |
| Installation | Hardwired, no power cord supplied. Ceiling and wall brackets included |
| Heat type | Fan-forced |
| Maker’s coverage claim | 600 sq ft |
| Safety listing | UL and cUL Listed, per the manufacturer's own specification. |
Who it is for
A garage or workshop where a published UL listing is the deciding factor, and where you want a thermostat you can set to a number and leave.
What it is not for
Anyone buying it for radiant heat because of the brand name — this is a fan-forced unit, and the radiant strategy for a garage is a different product entirely.
Sources for this entry
And what we did not do: we have not tested these units, owned them, measured them or run them in a room. Everything above is compiled from published manufacturer specifications and live retail listings, with the electrical load, room coverage and running cost computed by us from the published wattage. The full method.
Every roundup on this site names something to skip. It costs us nothing to publish and it is the fastest way to tell whether a buying guide was written for you or for its commission.
Heat tape and pipe heating cable
If your actual problem is a pipe rather than a space, heat cable wrapped on the pipe is the correct tool and a space heater is the wrong one — it uses a fraction of the power because it heats the pipe instead of the air around it. It is also not a space heater and is outside what this site covers, so we have no verified picks for it and will not improvise any. We are telling you this because the search that brings people here is usually about pipes, and the honest answer is sometimes a different product.
Any heater whose thermostat is an unmarked dial
This rules out most of the category, including several units we recommend highly elsewhere. A dial marked “low” to “high” cannot be set to hold 40°F — you set it by feel in a space you are standing in, and freeze protection is by definition a space you are not standing in. If you already own one, the fix is in the section below: a freeze-protection thermostat outlet does the deciding for it.
Propane and kerosene heaters in a crawl space
Unvented combustion in a sealed cavity under an occupied house is the worst version of a problem we cover in full on carbon monoxide. These are outside this site's scope — everything here is electric — but they are heavily marketed for exactly this use, so the position is worth stating rather than leaving to inference.
The headline spec on our top pick is a retailer's, not the manufacturer's. Several retail listings publish a 32–104°F thermostat range for the DR-218; iLiving's own product page confirms an adjustable thermostat with a precision temperature sensor and does not publish the range. We have pinned that distinction on the product card rather than smoothing it over, and given that you should be targeting 40–45°F anyway, the low end is not the spec your decision should rest on. Confirm it on the dial before you rely on it through a cold snap.
No maker in this category publishes a duty cycle, a minimum operating temperature, or an unattended-use rating. Nothing here is certified for "leave it alone for four months", because no such rating exists for portable heaters. The clearance rules still apply at 40°F exactly as they do at 70°F — three feet in every direction — and a space nobody visits is a space where a blocked intake goes unnoticed, which is a real argument for the fanless pick.
About 40–45°F. Just above freezing sounds right but leaves no margin: pipes sit in joist bays and against rim joists that run colder than the open air in the middle of the space, so the room can read 34°F while a pipe is at 30°F. Holding 40–45°F buys that margin.
It can keep the space the pipes are in above freezing, which is a different and less efficient approach than heating the pipes directly. If the pipes are the whole problem, heat cable wrapped on the pipe uses far less power — it is the right tool, and it is not something this site covers or has verified picks for.
Nobody can tell you honestly, because it depends entirely on how often the heater cycles, which depends on your insulation, air sealing and local weather. The ceiling is about $6.60 a day for a 1,500 W unit running continuously at our published rate; a sealed space holding 42°F will use a fraction of that.
No manufacturer certifies one for it, and no portable heater has an unattended-use rating. If you are going to, the measures that matter are a published low set-point so it idles rather than runs, three feet of clearance that nothing can encroach on while you are not looking, and ideally a fanless design or a Wi-Fi unit you can check from the house.
It needs to tolerate damp, and ideally be off the floor. Almost nothing in this category publishes a moisture rating at all — two of the four picks here do, at IPX4 and IP24, which is why they rank where they do. Note that an IP rating is water-ingress protection and is not a safety listing.
Only for a large one. A hardwired 240 V unit gives you far more heat and a thermostat that reaches 37°F, which suits a big crawl space, a well house or a detached outbuilding. For a typical residential crawl space held at 42°F it is more capacity than the job needs, plus an electrician.
Why the sizing rule under-sizes a basement by half, and the units that suit cold, below-grade space.
5,000 to 7,500 W, hardwired. The draw, the breaker each one needs, and four units whose manuals we read.
Three feet on every side, hard floor where possible — and the features that decide what happens if it tips.
No time limit on the appliance. The three real limits are the circuit, the bill, and the unattended-use advice.
Where the 10 W/sq ft rule comes from, when it breaks, and the exact watt-to-BTU conversion.
Mounting deletes tipping, floor clearance, cord routing and child reach. Plug-in panels and one hardwired unit.