Heat Your Narrowboat in Hours Without Losing Head Height.
Narrowboat underfloor heating
The expansive internal layout and domestic look and feel of narrowboats and widebeams lend themselves well to the concept of underfloor heating.
Some systems have succeeded where others have failed, so when Eberspächer UK’s inland waterways heating expert, Peter Collard, came across one system that worked particularly well, he was keen to find out more.
As Eberspächer’s marine technical engineering project manager, I am responsible for, and have been involved with, a great many different narrowboat heating system designs.
Among other things, I have been involved in a number of narrowboat and widebeam underfloor heating projects. Although all have worked, there have been varying degrees of success!
Until now, the boats I have been involved with would normally be fitted out using adapted household underfloor heating kits. Although these accomplished the job, they did have several drawbacks. Namely, household underfloor heating kits use relatively small internal diameter plastic pipe to heat under the floor.
This pipe requires a relatively large power-hungry water pump, sometimes requiring a household 240v pump.
These small pipes are normally plumbed into a complex water manifold delivery system and thermostatic mixer valves to regulate the amount of heat being sent under the floor and to control zone temperatures.
Valuable head height can be lost to thick underfloor insulation, pipe mats and overfloor covering.
These all serve to raise the height of the finished floor.
So can it be done?
Absolutely! But there are a few issues to get over.
1. Floor temperature:
A diesel-fired heating unit, like our Hydronic range, for example, will generally heat the system to 75–85°C.
I couldn’t envisage putting 85°C water under the floor!
I had visions of someone getting out of bed and hopping around like a cat on a hot tin roof!
2. Floor area:
Underfloor heating is low-temperature heat.
You need a relatively large floor area to compensate for heat loss — not easy in a narrowboat bedroom.
3. Flow rate:
A large water pump draining amps from the batteries is the last thing you want.
4. Head height:
Losing height to flooring layers makes life uncomfortable for anyone over 5'8”.
So when one of my customers said he had solved all of the above, I was sceptical — especially when he said he was putting 85°C water directly through the underfloor pipework! I had to see it for myself.
Does it work?
Yes — extremely well! The customer was JD Narrowboats, based at The Wharf, Shardlow, Derbyshire. I met director Andy Darken, who invited me to test one of their boats. One autumn day, I visited to monitor the underfloor heating over a six-hour period.
First impressions:
The boat had full head height and no radiators or plinths — very clean and spacious. It felt like a 9ft-wide boat rather than 6ft 6in. Open-plan design gave a large heated floor area. Furniture was raised off the floor to maximise efficiency.
I connected the Eberspächer heater to my laptop to monitor flow rate, temperatures, power, and voltage. It was running perfectly. The pipework layout dispersed flow efficiently.
I expected dangerously high floor temps — but it emitted a consistent, comfortable 32°C. The pipe size, water temp, and floor thickness combined for perfect dissipation.
The 58ft boat needed approx. 2.5kW to match heat loss at 0°C and 3–3.5kW to heat. Andy’s system was delivering around 3.5kW — ideal.
Is it worth it?
Yes — it was the most comfortable and evenly heated narrowboat I’ve experienced in 27 years. No hot-head, cold-feet issues like with radiators. No uneven heat due to poor radiator sizing or placemen