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Planning on extending your sailing season? Duncan Kent investigates diesel forced air heaters and finds out what is available on the market
Some of the online offers for diesel forced air heaters can look irresistible, but beware – they’re not all as they seem.
Duncan Kent is a technical writer for marine publications and websites
I strongly suspect that a good number of the low-cost, often cloned diesel forced air heaters available online do not conform to UK or EU laws and regulations, although confirming this is almost impossible without having them thoroughly tested here in the EU, by which time the original supplier has vanished into the ether and a new one taken its place.
Most budget diesel forced air heaters were originally designed for trucks or motorhomes, which have different requirements and are not subjected to such a vigorous environment as that found in a sea-going yacht.
Common issues are incorrectly designed exhausts, corrosive steel clips, screws and brackets, plastic fuel lines and filters, and non-watertight casings.
Some really cheap models lack thermal sensors, overheat alarms and shutdown modes, thereby presenting a very real risk of an onboard fire should the heat outlet accidentally be covered by a carelessly placed sail bag or drooping sleeping bag.
There’s also the possibility of carbon monoxide entering the boat if a fender is left dangling over the exhaust while the heater is running, or if the silencer is of poor quality with crimped, rather than welded seams.
All these are very typical scenarios found on a cruising yacht and highlight the need for the appropriate, built-in safety devices listed in the regulations.
Recent advances in diesel forced air heaters
As with most marine equipment, heating systems have been subject to gradual improvement over the past decade, both in regard to technical features and from a safety point of view.
Many are also now more economical on fuel and efficient on output, and the introduction of brushless fan motors has resulted in them using less electrical power and running much more quietly.
New glow ‘pins’ rather than the older style glow ‘plugs’ have greatly improved fuel burn efficiency too and gone a long way towards eliminating ‘coking up’.
Having a diesel forced air heater on board will extend your cruising season. Credit: Graham Snook
Many recent models now have a boost function just to pre-warm the boat and an eco-setting in which it just ticks over enough to retain the temperature within a narrow range.
There has also been a good deal of improvement in the controls.
In the past they’ve been simple electro-mechanical devices with either a rheostat or multi-way switch to select the temperature range.
Then along came more accurate controls with LCD displays and built-in seven-day timers.
Now, there are wireless remotes on offer and you can even control heaters by mobile app or online, so that you can switch the heater on when you’re a few miles away and climb aboard a toasty boat whatever the weather.
How much will a diesel forced air heaters cost me?
It’s important to work out what you need for your installation before attempting to compare prices.
Most kits come with enough bits for a single outlet and the minimal amount of ducting. So, if you want two outlets, you’ll need to measure carefully and price it in, along with a grill and a T-piece connector (£60).
Many owners now fit silencers to the fresh air intake as well, to quieten the ‘roar’ heard with older models, plus anti- vibration rubber mounts to lessen the sound of the fuel pump are also available.
A decent heater can transform winter sailing. Graham Snook finds out how the professionals go about installing a boat heater
The cost can increase if you want a fancy controller, too.
They usually come with just an analogue rotary-type knob with an LED or two to indicate operation status.
While this might suit some, others may want a remote panel with an LCD to show what’s going on (£150- £200), or even control via their phone.
Don’t be fooled by the ‘free’ app though, it’ll only work if the heater is connected to the GSM network, and that involves buying a modem and a SIM card (£200-£300, plus around £7.50/ month for the SIM).
If you get an advanced control box it’s worth fitting a temperature sensor. Finally, check how long the standard control cable is, as an extension can sometimes mean it’s cheaper and easier to opt for a wireless remote (£150).
Marine heater safety
Many of these heaters are designed for vehicles and don’t always list a specific marine kit.
Check the kit contains enough lagging to double-lag the exhaust and make sure the exhaust outlet is stainless or bronze and angled up to allow for a swan-neck in the pipe to eliminate back-feed of water.
It is also worth double checking the kit is marine specific.
Automotive heaters are designed to be fitted externally, so do not require the same standard of air-tightness on the joins around the exhaust and on the welds around the silencer.
It’s important to check and test your CO detector on a regular basis
Similarly, metal fittings may be galvanised rather than stainless steel, and vulnerable to rust, and fuel lines not of the same specification.
The critical safety issue is that of carbon monoxide.
A properly installed heating system will run without issue, but as we’ve seen too often, an exhaust leak or other fault can be fatal.
All boats should have a CO alarm anyway, but check yours is in date and working.
What diesel forced air heaters are on the market?
The upgraded system has a boost mode
One of the best known makes of marine heaters, Eberspacher, has recently upgraded its Airtronic heaters, giving them a power boost mode for fast initial heating plus continuously variable temperature settings.
They also now have a fresh air mode to improve air circulation through the boat on warm days.
Years of continual development has made these heaters more economical, quieter and more importantly, reliable.
The wide range of controls on offer includes various panels with switches and LCDs, or there’s the latest, EasyStart Call, which allows you to operate your heater using the proprietary smartphone app.
The app turns your phone screen into a simulated control panel and transmits your selected settings to a GSM module installed in the heater.
Models include the Airtronic D2 and S2 D2L (