Idle Worship

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Idling a big, brawny diesel engine is bad news. That’s a given, but zero idling is a complete impossibility, not even a useful target. If you’re at a 25-percent idling rate you’re already doing well and a fancy $10,000 APU is unlikely to be of any use to you. Even then, there’s work that can be done, but if you’re at 50-percent idling or more, there’s lots you can do to save a buck.

Quite apart from the ugly cost side of this, there’s the profusion of jurisdictions with laws that aim to limit idling trucks, but they’re all different. So it’s a confusing picture at best, even if your routes are ­regular, because things change all the time. This confusion certainly doesn’t help with compliance.

What to do? Well, one manufacturer of auxiliary power units (APUs) probably has the right idea in suggesting you make a lowest-common-denominator assumption.

“Because of these wildly varying laws it’s best to adopt a best practice of say no more than five minutes of idle time in the United States and no more than three minutes in Canada,” they say.


It’s a bit wild and woolly out there in anti-idling land, and solutions are thick on the ground. The trick is finding one that works in your particular case. As the American Environmental Protection Agency’s (EPA) SmartWay folks define things, there are five main option categories: fuel-fired heaters; battery-based HVAC systems; auxiliary power units; thermal storage systems; and the obvious shorepower, in the unlikely event that your driver can find a plug.

We’ll add training and educating your drivers to shut the diesel down whenever they can. And then backing it up with an incentive program.

Fact is, there are so many alternatives within some of the five categories we listed that you’re probably not quite sure where to turn.

If you look at the EPA’s current list of devices that would qualify for a federal excise-tax exemption in the U.S. the total number is about 60, from small diesel-fired bunk heaters to full-bore auxiliary power units and the increasingly common electric HVAC systems. It’s very hard to keep up. Your truck dealer can help sort things out, and in fact most truck-makers now have a ‘proprietary’ system of their own, most of them electric.

What’s common amongst all of them is that payback on your investment can be quick in theory, sometimes even within a year. After that you’re saving money on fuel — possibly thousands a year — and your drivers no longer have to wear 16 pairs of longjohns or strip down to their skivvies depending on the season. That’s a win/win situation if ever there was one, and don’t underestimate the effect this can have on driver recruitment and retention efforts.

Your choices depend, as always, on what sort of trucking you do and where you do it. Your options will cost anywhere from $1,500 to well over $10,000. In general terms, this is what’s on offer:


This is the simplest and easiest solution if you don’t need cooling. It might list for something like $1,200, cost a few hundred to install if you don’t do it in your own shop, and for about the same amount again you can add an engine heater.

Say your trucks idle eight hours a day for 35 weeks of the year to keep your drivers warm, and a little bunk heater will sip about 0.25 litres of fuel an hour, compared to three or so for your big Cummins. So you’ll spend about $490 instead of $5,880 on that fuel in a year, assuming diesel at $1.40 a litre. Eight hours and 35 weeks may be too many, of course, but payback can clearly be quick.


Increasingly common are battery-based heating/AC units that also provide ‘hotel’ power to run microwaves and the like, never needing the truck’s engine at all. Typically these systems provide heating, cooling, and 110-volt power for up to 10 hours. By and large they’re a bit cheaper than diesel-powered APUs, but make sure they offer the cooling capacity you need. 

shorepower is an option, but not without its challenges

While the truck is being driven, a beefed-up alternator of 185 amps or so charges a power pack consisting of deep-cycle batteries and an electric air-conditioning compressor charges a thermal storage unit. When activated, an electric fan circulates cold air though the thermal storage unit and into the sleeper. Heat is usually supplied by a small diesel-fired unit.

They’ll need about eight hours of charging — that is, running the truck and its alternator — before they’re ready to go again, which may restrict their application. Most offer a shorepower option.

When you add the weight of three or four deep-cycle batteries, you’ll be at or even above the weight of an APU, in the range of 400 lb.

There are also smaller electric units that provide AC only, others that offer just heat, even for near-Arctic conditions. Some will run on 110/115 volts off an APU, off a bank of on-board deep-cycle batteries, or off a shorepower connection.


Producing their own power by way of one-, two-, or sometimes three-cylinder diesel engines, these range from about $7,000 to $13,000 or so, installed, and at least one supplier offers leasing.

If you spend time in hot climates or pretty much live in your truck and want all the electrical pleasures of home, the advantages are real. Most APUs will run their own integrated AC compressor, condenser, and heat exchanger, and won’t need to tie into the truck’s system. Some include a power inverter as standard equipment, some call it an option.

At least one APU can integrate additional power in an available hydraulic pump, pneumatic compressor, or additional alternator for DC and AC power. That same unit can run on propane as well as diesel.

APUs consume about an eighth as much fuel as the truck’s big diesel, give or take, so there’s serious money to be saved. Payback can be just a couple of years, but that depends entirely on duty cycles and routes travelled.

Unfortunately, a lot of fleet managers have been turned off the APU idea because things haven’t gone well in the past.

Unreliability has been an issue, meaning only about one truck in 10 is APU-equipped, though it’s not the same problem it once was.

Some weigh over 500 lb, routinely around 400, which may be a factor. Some APUs — depending on how much frame-rail space they need — will be either expensive to fit or even impossible on trucks with elaborate side fairings and, nowadays, DEF tanks. They usually need about 24 in. of frame rail.

You definitely want an APU with automatic low-battery-voltage protection, though you may have trouble finding one without it any longer.


The shorepower issue is an article in itself so we’ll leave it pretty much alone here. You can get your trucks fitted with shorepower capability easily enough, and then — if a connection can be found — your drivers can run small appliances like stand-alone household air conditioners and heaters. Moves to ‘electrify’ truckstops have not been successful, though efforts continue.

A thermal energy storage system is also a possibility, at least for cooling, though there aren’t many available and they won’t cool an already hot sleeper very effectively. The idea is that cooling energy from the vehicle’s own AC system is captured and stored during normal road operation, then used to keep the cab cool later when the engine is off.

One of the key challenges in all of this is right-sizing. If you’re looking at a heater, a common recommendation is that you need about 1.0 kW of heating capacity for a small sleeper up to 48 in. in length, as much as 2.0 kW for a 72-incher.

On the cooling front, you’ll want 7,000 BTU/hr for a day cab or small sleeper, double that for 60- or 72-in. bunks. There’s no research to back this up, but experts say that if there’s dissatisfaction with anti-idling devices, it may well arise because they’re not always spec’d to match the need.

And then there’s insulation. Chances are, you haven’t thought much about the insulation in your trucks, but you should — before you go spec’ing anti-idling hardware on a new truck.

The TMC Recommended Practice calls for at least R4.2 as a standard insulation package. Compare that to the R1 that most truck sleepers are insulated with today and you see a wide discrepancy. Even so-called cold-weather packages don’t necessarily meet the TMC standard.

Deciding what’s best for you and your trucks may be somewhat complicated, but you’ll have to do something to limit idling as more and more jurisdictions demand it.

Or, sooner still, as the price of fuel forces your hand.

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Rolf Lockwood is editor emeritus of Today's Trucking and a regular contributor to

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