Diesel Heater for a Dog Van: 2.5KW vs 5KW + CO Safety

A work van carrying dogs needs anywhere from 1,000 W to over 5,000 W of heat at -4°F (-20°C), and the biggest single variable is insulation rather than the van. A mid-size cargo van with camper-grade insulation needs 1,641 W. The identical van, bare metal with an unsealed bulkhead, needs 5,211 W. That is a 3.2× spread on one vehicle, and it is why two people driving the same van will give you opposite advice about heater size.

This guide is written for the people who have to leave dogs in a vehicle during the day: show exhibitors between rings, gundog handlers on a shoot day, groomers and pet transporters between jobs, and rescue volunteers on long transport runs. It is not an RV build guide. The design priorities are different, and copying a camper-van heating layout into a dog van gets two of the three important things wrong.

Why a dog van is not a camper van

Three things change, and each one pushes the design in a different direction from an RV build.

The target temperature is lower. A camper build is sized to hold 68°F (20°C) because a person is sitting still in it reading. A crated dog in winter coat is comfortable at 45–55°F (7–13°C), and the working consensus on hunting and field-trial forums lands around 58–62°F (14–17°C) for boxes with heat fitted. Designing to 50°F (10°C) instead of 68°F (20°C) takes about a quarter off your heat demand before you have bought anything.

The occupants cannot leave and cannot tell you anything. A person in a camper opens a window when it gets stuffy. A crated dog cannot. Every failure mode that a human would notice and correct within thirty seconds — a stuck thermostat, an exhaust leak, a vent that got blocked by a kit bag — runs unchecked until you come back.

The dogs are a heat source and a moisture source. A resting 30 kg (66 lb) dog gives off about 43 W of body heat, using the standard veterinary resting-energy formula. Four of them is roughly 175 W, which sounds trivial next to a 1,600 W load until the van warms up, the heater throttles back, and the dogs keep producing heat and water vapour in a box you have carefully sealed. This is the mechanism behind the winter overheating stories that circulate in hound circles, and it is real.

Size it with K-value math

Heat demand is surface area times an insulation coefficient times temperature difference, plus the cost of air exchange. Vehicle heating has used this method for decades. Nothing here is proprietary and you can check every number yourself:

Q (W) = A × K × ΔT + 0.359 × V × n × ΔT

• A = internal surface area in m², = 2 × (L×W + L×H + W×H)
• K = insulation coefficient in W/(m²·K) — the number that decides everything
• ΔT = target inside minus design outside, in K
• V = internal volume in m³, n = air changes per hour

The K value is the whole argument

Real numbers for four common dog vans

Design point below: dogs held at 50°F (10°C), outside -4°F (-20°C), ventilation at 3 air changes per hour — higher than a camper build because dogs put out a lot of moisture.

Milder weather scales straight down. Heat demand is linear in ΔT, so at 20°F (-7°C) outside multiply every figure by 0.56; at 30°F (-1°C) multiply by 0.37. A ply-lined mid-size van needs 2,710 W on a -4°F morning and about 1,520 W on a more typical 20°F show day.

What the table says about insulation

2.5KW or 5KW: what the two models actually do

Pick the model that puts your calculated load between 40% and 80% of real output. Note that word real: the 5KW unit is rated 5,000 W but its Boost step is 4.7 kW, so size against 4.7 kW, not 5.

Mapping the sizing table onto those two: a camper-insulated compact or mid-size van is a 2.5KW job, landing at 41–66% of output. A ply-lined mid-size (2,710 W), an insulated full-size high roof (2,430 W) and an insulated box body (2,850 W) are 5KW jobs at 52–61%. Two cases sit awkwardly: a ply-lined full-size high roof at 3,970 W runs the 5KW unit at 84%, just over the band, and a ply-lined box body at 4,650 W is at 99% — that one is an insulation job before it is a heater job. Bare metal anything is not a heater problem yet.

Why oversizing is worse here than in a camper

An air heater sized far above its load spends its life short-cycling: fire, glow plug, run at minimum for a few minutes, shut down, repeat. Two things follow. Carbon builds up in the burner because low-power running never gets hot enough to clean it, which is the single most common cause of a unit that smokes and eventually will not light. And every restart re-fires the glow plug, which is where your battery actually goes (see below).

A unit running steadily at 60% of rated output is quieter, burns cleaner, draws 1–2 A instead of spiking to 10 A every twenty minutes, and holds a much flatter temperature. For a box you are going to leave alone for three hours, that is what you want.

CHOOSE 2.5KW OR 5KW →

Carbon monoxide when nobody is in the van

A diesel air heater keeps combustion sealed from the air it heats — two separate circuits that never meet inside the unit. Outside air is drawn in through the intake pipe, burned, and pushed out through the exhaust. Cabin air passes over the outside of the heat exchanger and back into the van without ever touching combustion gas. With a correct installation, no combustion gas reaches the dog space.

That sentence rests entirely on the word correct. Here are the five ways it stops being true.

The five ways CO gets into the dog space

1. A leak in the exhaust between the burner and the tailpipe. Cheap clamps, a cracked gasket at the combustion chamber, or a through-floor penetration that has worked loose with vibration. This is the common one.
2. Exhaust re-ingestion. If the exhaust outlet and the combustion air intake terminate close together, or both sit in a wheel arch or behind a skirt where fumes pool, the heater breathes its own exhaust. Output drops, combustion goes rich, CO climbs.
3. Incomplete ignition on restart. Owners on boat and van forums report the same pattern repeatedly: the alarm trips when the heater cycles off and back on, then a long continuous run goes hours without a peep. Rich combustion during startup is a real CO source, and a short-cycling oversized unit does it all day.
4. A recirculation intake in the wrong place — pulling cabin air from a spot where exhaust can reach it, typically a floor-level intake near the exhaust exit.
5. A cracked or perforated heat exchanger. This is the one failure you cannot inspect from outside the unit, and it breaches the separation between the two circuits directly. It is rare, it is what stainless combustion chambers are built to resist, and it is the reason a CO monitor is not optional equipment on a dog van.

What a CO alarm will and will not catch

What to do about it, in order of usefulness:

• Fit a low-level monitor with a ppm readout rather than a pass/fail alarm. Devices that display from around 5 ppm let you see a slow leak developing weeks before a UL 2034 alarm would make a sound.
• Mount it at crate height. CO is close to the same density as air and diffuses evenly — the ASPCA is explicit that animals near the floor are at no more risk than taller ones. Put the sensor where the dogs breathe because that is what you are measuring, not because the gas sinks.
• Check the date on it. CO sensors have a service life of about five years, after which the unit still lights up and still beeps on test but is no longer measuring anything.
• Rule out the batteries. More than one owner has chased phantom alarms for weeks before finding that failing lead-acid batteries inside the living space were gassing, with the heater switched off the whole time.

What CO poisoning looks like in a dog

Early and easy to miss: lethargy, vomiting, tiring quickly, drooling or lip-smacking, uncoordinated movement. A distinctive sign is abnormally red gums. Behaviour changes too — new anxiety, noise fear, or uncharacteristic aggression are documented signs. Severe exposure moves to laboured breathing, seizures, collapse. Get the dog into fresh air and to a vet immediately; oxygen is the treatment and it takes hours.

Ventilation: why sealing the van is the mistake that kills

Every extra air change per hour costs about 67 W in a mid-size van. Run that against the table above: on a 2,710 W load, going from 3 to 5 air changes per hour adds 134 W — about 5% of the heat bill, and roughly 0.01 L/hr of extra diesel. There is no version of this trade where sealing the van to save fuel is the right call.

Three reasons the sealed van is the dangerous one

Winter overheating is not a hypothetical. The story that circulates in houndsman circles — a new well-insulated aluminium box, closed up tight and packed with straw for a long drive, outside temperature in the teens, and not all the dogs came out alive — is the predictable result of body heat with nowhere to go. Four resting labs put out 175 W into a sealed 6 m³ box. Nothing removes it.

Moisture has to leave. Dogs breathe out a lot of water. Handlers describe steam coming out of a kennel when they unzip it in the morning, and condensation freezing on box doors overnight. A sealed van gives you wet bedding, wet dogs and a much colder dog than the thermometer suggests.

It is now a rules problem, not just a physics problem. The AKC adopted an Unattended Dogs in Vehicles Policy in July 2026, effective immediately. It prohibits leaving a dog unattended in a vehicle that is "fully enclosed or does not have adequate ventilation and airflow." The definition of vehicle explicitly covers vans, commercial vehicles, trailers used to house dogs, motorhomes and RVs. Penalties run from a one-year suspension and a fine up to lifetime suspension and $10,000. The source documents sit on akc.org/rules.

What adequate airflow actually looks like

• Two openings, diagonal, low and high. Low inlet on one side near the front, high outlet on the opposite side at the rear. One vent achieves very little.
• A powered roof vent on low gives you a known air change rate instead of a hopeful one. Most draw 1–3 A and can run off the same leisure battery.
• Keep the paths clear. The most common real-world failure is a kit bag, a grooming table or a stack of crates parked against the outlet.
• Do not block factory vents to "help" the heater. That is exactly the move the AKC policy is written against.

Power: what actually goes flat

Startup pulls about 8 A at 12V for the glow plug; running settles to 1–2 A. The steady draw is not the problem. Four hours of continuous running is roughly 15–20 Ah, which any healthy leisure battery handles without noticing.

The complaint you see on every van forum — "woke up to a flat battery" — almost always traces to cycling. Every time the thermostat calls for heat, the glow plug fires again, and owners who have clamp-metered the circuit report it climbing back to 10–12 A on each restart. A unit that cycles fifteen times overnight has run its glow plug fifteen times. This is the practical reason the 40–80% sizing band matters: a correctly sized heater loafs along continuously instead of hammering the battery every twenty minutes.

The second failure catches people out: the heater stops being able to start well before the battery is actually dead. It needs real current for the glow plug, so a sagging battery means no heat on the coldest morning of the trip, with everything else in the van still working fine.

• Run a dedicated leisure battery, not the starter battery. A starter battery plus a three-day show weekend plus a heater is a recovery call.
• Size for at least three nights of autonomy.
• Fit a low-voltage cutoff, and set it above the heater's start threshold rather than at the battery's protection limit.
• Check the cable gauge. Voltage drop in thin factory loom wire is a common cause of hard starting; 6 mm² on the supply run fixes a surprising number of "faulty heater" complaints.
• Portable power stations with a regulated 12V/8A output are marginal for the startup spike. Wire to a battery.

The install, where it differs from an RV

The heater body belongs outside the dog compartment — underfloor, in the front footwell area, or in a box that is sealed against the dog space with the combustion air intake and the exhaust both ducted through its wall to open air. This is the single biggest divergence from a camper build, where the unit typically sits under a bench inside the living space. Get the enclosure wrong and you create failure mode two: an airtight box starves the burner, combustion goes rich, and CO climbs. Sealed against the dogs, open to outside air.

The rest of the differences:

• Separate the intake and exhaust properly — opposite sides of the chassis rail where you can, both terminating in clear airflow, neither in a wheel arch or behind a skirt.
• Never duct warm air straight into a crate. Aim the outlet along the roofline or into the aisle so the air mixes before it reaches a dog. A dog that cannot move away from a 175°F air stream is a burn risk.
• Route the warm-air duct above crate height, and drop it at the far end. That gives you circulation the length of the van rather than one hot crate and three cold ones.
• Armour every cable and fuel line the dogs can reach. Split conduit at minimum. This is not a theoretical risk with bored young dogs.
• Use proper exhaust pipe with real clamps. The 304 stainless spiral exhaust pipe is the part that decides whether failure mode one on the CO list ever happens to you. Thin single-wall tube cracks at the bends.
• Put a thermostat sensor at crate height at the far end of the van — not on the controller next to the outlet, which will read 8–10°F warmer and shut the heater off too early.

The general install sequence, fuel pickup and mounting angles are covered in the five precautions for diesel heater installation, which apply here unchanged.

Before you load dogs: a working checklist

1. Preheat the van before the dogs go in. Frozen condensation on the doors from the previous run needs time to melt and dry, and a cold crate takes a long time to come up once a wet dog is in it.
2. Run the heater to full temperature and watch the exhaust. Clear or light haze is normal. Persistent white or blue smoke means a burner problem — see diesel heater troubleshooting before you travel.
3. Check the CO monitor reading, not just that it is powered. Anything above zero with the heater at temperature needs investigating before you leave the van.
4. Confirm both vents are physically clear after loading, not before. Things get stacked against them during loading.
5. Put a thermometer probe at the far crate and check it against the controller. Learn the offset for your van once.
6. Use winter-blend fuel below 20°F (-7°C). Gelling in the heater's own pickup is a slow, annoying failure; see how to prevent diesel fuel gelling.
7. Set a check interval and keep it. The AKC policy requires regular checks but sets no interval. Forty-five minutes is our number, not theirs, and it is short enough to catch a stalled heater before the van gets cold.

Frequently asked questions

Related guides

• Diesel heater for a camper — the full sizing and install guide for a living-space build, where the target temperature and layout rules are different from a dog van.
• Five precautions for diesel heater installation — mounting angle, fuel pickup and exhaust routing, with the mistakes that cause most first-install failures.
• How to choose the best diesel heater — what separates units that last from units that are cheap, component by component.