Underfloor heating

In an earlier post, I mentioned my wish to have underfloor heating - or UFH.

UFH can be either a web of electric heating elements or a series of pipes filled with water. Electric is impractical on a boat, but wet UFH can be heated with any normal heat source. The vital thing is that the pipes are set into highly insulating boards, to prevent heat loss on the wrong side. Quality insulating panels also have a metal layer on the top surface, to help spread the heat.

There were a number of reasons why I liked the idea of UFH. Having already committed to the idea of a central heating cooking range, I would have ample hot water. I didn’t really want the coal storage, dust and ash disposal issues of a solid fuel fire. Most particularly, I didn’t want the ‘roasting saloon/freezing bedroom’ problem, so often encountered. Plus, we don’t like our dogs roasting themselves in front of a fire. It’s not good for them, but hard to prevent. Another perennial problem is heating the bathroom. The ‘smallest room’ has the least space to install a radiator, but really needs the most heat! Finally, I find that radiators take up quite a lot of room and can be knee-cracking annoyances. UFH could address all these points.



However, an issue which was identified quite early on, was the resulting thickness of the floor. In order to prevent heat being lost to the bilge, a high quality insulation layer is needed. So on top of the normal 18mm ply floor would be a 25mm insulating/pipe layer, with another 18mm engineered oak layer on top of that. So it looked like the headroom would be reduced by 43mm, compared to a standard ply floor. I didn’t relish the idea of losing nearly 2” of headroom.





I came up with a novel solution to overcome this problem. Normally, the 100cm sheets of steel used to form the cabin side are taken up beyond the roofline to form the handrail, which is about 40mm

high. But by using the whole of the sheet width as the cabin side, it would be possible to very nearly regain the lost headroom. The handrail would then be formed from D-section (rubbing strake) steel mounted on studs to form a ‘rat-trap’ rail. In my view, this brings other benefits, such as not trapping dirty water and allowing rainwater to run off along the boat, rather than being channelled in one small area. The guys at XR&D agreed that the slightly higher cabin side wouldn't upset the balance of the boat design. Tick.


One of the main reasons people don’t adopt UFH on narrowboats, is the lack of exposed floor area, because much of it is covered by cupboards and other furniture. Fair point – UFH is a low grade heat which requires a large radiating area. However, I could also see a benefit in having, for example, the under bed storage being gently warmed.

I pondered this problem for quite a while, then had a lightbulb moment. Why only use UFH under the floor? The boat sides are about a metre high. The two sides equal the width of the floor and are largely, more exposed. So why not continue the UFH insulating boards and pipework up the sides? A call to a UFH specialist company confirmed that they could see no reason why it wouldn’t work, as long as there was a good air removal device in the system.

The idea worked in well. The vertical side bearers are 50mm deep, so this space will be filled by 50mm Celotex. On top of the bearers will be three 25mm longitudinal battens. Between the battens will be two 415mm strips of 25mm UFH insulation panel. Each strip will be able to house three runs of pipe at 150mm centres. I am even considering running UFH pipes through the bulkhead behind the shower to provide additional warmth.

This arrangement should result in a U-section of gentle radiated warmth, extending the length of the cabin. I anticipate that this will provide a comfortable environment, which will be controlled by a thermostat.

Ballast. There is also another issue, frequently not commented upon. Given the construction sequence: ballast, battening, plywood, insulation, pipework, finish floor, furniture and fittings, the slightly scary realisation was that the ballast, once in, will be inaccessible. This meant that very accurate calculations would be needed to ensure that ballast will be located in the right quantity and location – fore/aft and left/right!
In order to try to get the ballasting of the boat right, I am working with a spreadsheet which takes into account the total weight of an item and how far left or right of the centreline it will be located. So for example, the cooking range weighs around 400Kg. Its centre will be 300mm from the left side, roughly two thirds of the distance from the centreline. So the effective weight being applied to the left side of the boat is 266Kg. By repeating this exercise for all of the significant items, I should be able to get within the realms of correctable ballasting. In practical terms, this means shifting some 56lb weights around!

The design of the UFH system should result in about 40m2 of UFH area, of which about 60% will be exposed. Given the high insulation value of the boat - even the cabin sides and roof will have 50mm Celotex - this should be very adequate and result in cosy warm floors.

Back up. In recognition of the fact that I will have a lot of eggs in one basket, I also plan to install a small multifuel stove, just for emergencies or effect when required. This will help to counter the problem of a complete failure of say, the burner unit in the cooker.

Cost. The installation of UFH is not a particularly costly exercise and is very comparable with the cost of decent quality radiators, pipework and valves.