For a garage box holding an NVR, a router and a UPS, the honest answer is: work out the heat load first, and expect the number to point at a fan, not vents. A sealed steel enclosure around 20 x 16 x 8 in (500 x 400 x 200 mm) can dissipate roughly 20-40 W of equipment heat while staying within 15-20 C above ambient, depending on airflow around it. A three-device load of 40-90 W in a 40 C (104 F) garage will not stay sealed and cool at the same time. You have to give something up: either the sealing, by cutting vents and fitting a filtered fan, or the heat, by choosing hardware that runs cooler.
Add up the heat load before anything else
Every device inside the box is a heater. Nameplate power overstates it; typical running draw is what matters.
| Device | Typical running heat |
|---|---|
| 16-channel NVR, no drives | 10-15 W |
| Each 3.5 in surveillance HDD under write load | 6-10 W |
| Router or modem | 10-20 W |
| Small UPS, on line, lightly loaded | 10-30 W |
For a two-drive NVR plus a router and a UPS, plan for 50-90 W. The UPS matters more than people expect, and it is often the one item nobody counts. Its efficiency curve is worst exactly when the battery is charging after a power cut.
What a sealed box can actually dissipate
A sealed enclosure loses heat three ways: conduction through the walls, convection off the outside surface, and radiation. A rough working number for a painted or stainless box of about 0.13 m² of surface area is 3-5 W per square foot per 10 C of allowable rise. A 20 x 16 x 8 in box has roughly 9.8 ft² of surface. At 15 C of allowed rise, that is on the order of 45-70 W of dissipation with free air around it, less if the box sits in a corner or near a wall.
Three things push that number down fast:
- High ambient. A garage that touches 40 C leaves only 15-20 C of rise before you hit the drives' 60 C operating ceiling.
- Wall mounting against an insulated wall cuts natural convection on the back face.
- A UPS charging after an outage can double its heat output for an hour or more.
If your load is under roughly 30 W, sealed works. Above that, in a hot garage, it does not.
Sealed and safe: the no-cutout option
If you can keep the box sealed, do it. A gasketed stainless wall-mount box, manufacturer-rated NEMA 4X / IP66; not UL listed, keeps dust, insects and hose water out, which is exactly what you want near lawn equipment and stored cardboard. To stay sealed with real hardware inside:
- Choose a low-power NVR, or accept that drives idle-spin-down between events.
- Fit the equipment to a removable mounting plate rather than the back wall, so conduction into the wall is not the path.
- Leave 1-2 in (25-50 mm) of air space above and below the heat sources; internal convection still works in a sealed box.
- Add an anti-condensation heater or a hygrostat-controlled strip if the garage swings between cold nights and humid days; condensation in a sealed enclosure is a real failure mode that no ingress rating prevents.
- Put a temperature logger inside for a summer week before you declare victory.
If the load will not fit under the sealed limit, the enclosure does not have enough steel to lose the heat. Move up a size or change the plan. The guide to removing heat from a small sealed enclosure covers the conduction and layout tricks in detail, and component layout inside a sealed enclosure explains where the heat sources should sit.
Vents and a fan: what you give up
Cutting vents into a gasketed box ends its ingress rating. That is not a technicality: the rating exists because the gasketed seams pass a jet of water and a dust test, and a drilled hole with a mesh grille passes neither. Practical points if you go this way:
- Put the fan low on one side or the bottom as an intake and cut exhaust holes high on the opposite side, so air crosses the heat sources.
- Fit washable filter media on the intake. A garage is a dust machine; an unfiltered intake imports it.
- A single 120 mm fan at even 5 V moves plenty of air for 100 W of equipment; noise falls faster than cooling does when you slow a fan down.
- Keep holes away from the door gasket line and away from any point where a hose could ever be pointed at the box.
- Power the fan from the UPS-protected side, ideally through a thermostatic control so it only runs when needed. A bimetal snap switch rated for the fan's current, set around 35-40 C, is the simple version.
For the rating side of this trade, see putting a fan on a NEMA 4X enclosure, and for the cooling options beyond a simple fan, fan vs air conditioner vs heat exchanger. Above roughly 150-200 W of load in a hot space, a filtered fan stops being enough and you are into heat exchangers or air conditioners; cabinet air conditioner sizing is the next stop.
Choosing the enclosure to start from
If you are specifying the box rather than converting one, size it for the option you might need later. A 20 x 16 x 10 in (500 x 400 x 250 mm) box gives a deeper mounting zone for a UPS and space for a future fan plate, and both 304 and 316L versions come in the same footprint. We build these to order with the cutouts you specify, delivered in 10 business days from drawing approval for custom work, so it is cheaper to decide vent positions now than to drill later.
- If sealed is realistic: 20 x 16 x 8 in 304 stainless wall-mount enclosure, gasketed door, mounting panel, no cutouts.
- If you want depth for a UPS and a fan plate: 20 x 16 x 10 in 304 stainless wall-mount enclosure.
- For coastal or washdown-adjacent garages: 20 x 16 x 10 in 316L stainless wall-mount enclosure.
All of these are manufacturer-rated NEMA 4X / IP66; not UL listed. If your specification or local inspector requires a listed enclosure, confirm that before ordering.
A quick word on standards: a NEMA 4X-type rating and an IP66 code describe different test regimes, and in US installations an IP rating is not a substitute for an enclosure type rating. The NEMA 4 vs 4X vs IP66 guide explains the difference, and how an IP water test works shows what the box actually survives.
The decision, in one pass
- List every device in the box and write down its realistic running draw. Include the UPS.
- Add 20-30% for charging transients and warm drives.
- Compare the total against 30 W for a sealed box of this size in a 40 C garage.
- Under the limit: keep it sealed, lay out for convection, log the temperature for a week.
- Over the limit: plan filtered forced ventilation from the start, cut intake low and exhaust high, and drop the ingress rating from the specification.
- Well over 200 W, or sun on the box: escalate to a heat exchanger or air conditioner.
The sizing method behind step 1 and 3 is laid out in how to size an electrical enclosure, and the heat arithmetic in the enclosure heat calculation guide. If you are unsure whether the box you have in mind can be kept sealed, the enclosure selector filters by environment and inside size and flags when high ambient needs a closer look.
The one mistake to avoid: drilling vents into a rated box and then continuing to specify it as sealed. Decide which trade you are making, write it on the drawing, and build the box for it.
Questions
Will drilling a few vent holes ruin the IP66 rating?
Yes, effectively. Any hole drilled after manufacture breaks the gasketed seal the rating depends on, and small holes do not meet the jet and dust tests the rating describes. A vented box should be treated as a drip-shielded enclosure at best. If the rating matters for the installation, keep the box sealed and move the heat out by conduction instead, or specify a purpose-made vented box and drop the ingress rating from the spec.
How much heat does an NVR with two hard drives produce?
A 16-channel NVR idles around 10-15 W and climbs toward 30-40 W with two spinning hard drives under write load. Add a router or modem at 10-20 W and a small UPS on line at 10-30 W depending on model. A realistic total for a three-device garage box is 40-90 W, which is far beyond what a small sealed enclosure can dissipate passively in a 40 C ambient.
Can I run a fan from a USB port on the NVR?
Technically a 5 V USB fan will spin, but it is poor practice. USB ports on NVRs and routers supply limited current, and a stalled or failing fan can drag the rail down and reboot the device it is supposed to protect. Power the fan from its own small supply or from a spare output on the UPS-backed side, and size it for the enclosure's air gap, not for convenience.
Is a fan really necessary if passive cooling seems adequate?
Measure first with a temperature logger over a hot week. If the interior stays below the drives' maximum specified operating temperature with margin, passive is fine. But hard drives rated to 60 C ambient will run short of that in a sealed box, and a small filtered fan costs little and adds margin. Many builders fit one anyway for exactly that reason, then set it to run only above a threshold.
Does a garage need a stainless enclosure?
Usually 304 stainless is enough for a dry, unheated garage; the rating matters more than the alloy. 316L earns its cost near salt air, coastal garages or washdown areas. Both grades of our wall-mount boxes are rated NEMA 4X / IP66 by the manufacturer; not UL listed, so check whether your specification or inspector needs a listed enclosure before ordering.
