Monday, 10 December 2012

Condensation in narrowboats

When we were last on Jubilee, a couple of weeks ago, we had pointed out to us a condensation problem. At least, I assume it's condensation. The outside temperature was low; the stove was on; and there were four of us breathing and cooking inside. The windows were running with condensation, which wasn't a problem as I'd recently cleared the "limber holes" to allow the water to drain to the outside.

(I discovered the name of these holes only when reading the December issue of Canal Boat magazine.)

The problem? Water was dripping from under the gunwale onto the pillows of the convertible dinette bed.

Looking under the gunwale I can see the 1/2" copper gas pipe, and not much in the way of spray foam insulation. I don't know if it was cut away in order to route the gas pipe through, or if this area never got the spray foam treatment. I'm fairly sure, though, that this is the reason for the damp pillows (and the damp seat cushion when in its normal use as the dinette).

I think the solution will be to spray more foam up there. Is there any regulation about not spray foaming a gas pipe? Does anyone know?

Incidentally, an article about condensation in the December Canal Boat mag is followed immediately by Tony Brookes's advice column. The two articles seem to differ in their recommendations regarding ventilation. The first (author anonymous) article warns against "excessive" ventilation, as "cold and persistently damp winter conditions can bring in more moisture than it vents out" (p86). Tony Brookes, on the other hand, advises keeping "as many window hoppers open as you can to help ventilation throughout the boat. This will go a long way to reduce condensation problems."

So what is one to do?


Sue said...

It doesn't matter what I do.. Open the 'hoppers' or keep the boat shut up..

All I really want to do is keep warm. So I shut up and worry about it in the morning.

We have condensation on all the windows in the morning whatever we do, so put up with it now.

It doesn't take too long to rid it though.. A good wipe around takes most away.

The biggest problem we have is at the bottom of cupboards in winter.. those places tend to get damp, but I don't want to put vents in cupboard doors.

I put mini pallets on the bottom of cupboards which keeps stuff off the floor.

Once a week I wipe the floors in them..

It's a matter of keeping warm and dealing with the condensation I think

Bruce in Sanity said...


Yvonne on Fizzical Attraction has just blogged about secondary double glazing for windows, using acrylic sheet and magnetic tape. Chasing condensation is a never ending job; we just found a little patch in the corner of a cupboard against the front bulkhead.

The problem is, the more you insulate one area, the worse it tends to get elsewhere. I'm doubtful that you can spray foam over gas pipe, you might have to put a strip of ply over it instead, but the guys over on CWDF would be able to say for sure…

Good luck with it!



Anonymous said...

Hi Halfie,
good ventilation absolutely helps keeping condensation at bay.
Reason is the physics of it:
Cold air can hold only very little moisture, warme air holds much more.
So if cold air gets into the boat its gets warmed up and hence "dry". This means it can "soak" up moisture. But that means you need some draught to get the then wet warm air out a gain and fresh cold air back in.

With the gas pipe: The pipe might acctualy be the reason for condensation as the gas getting in is very cold. Its cold in the bottle allready, but when getting decompressed in the regulator it gets well below zero, hence the pipe gets very cold: ideal for condensation.

A solution might be is to get a removable lagging for the pipe. Dont know if thats allowed though. You moght want to ask a BBS inspector.



Elsie said...


We've used secondary double glazing which uses double sided sticky tape and a plastic film so we only get condensation on the windows which aren't double glazed as we need to be able to open them.Bought it from a hardware now we have fewer windows to wipe in the morning.

Regards Elsie (NB Bendigedig)

Dave Winter said...

Following Elsie's comment I have just posted about this film on my blog.

Neil Corbett said...

We too have secondary double glazing which we put in in winter and it really does eliminate nearly all condensation. Ours is made of clear tent window plastic stapled to a wooden frame. The frames are a tight push fit into the boat's window frame which I think is important.

Next time you see us come and have a look.


Halfie said...

Sue, yes, it's important Ally and Ben keep warm! I'll have to get them to check cupboards - good idea. Thanks.

Bruce, when I get a moment I'll see if I can check what the BSS says about gas pipes. Slightly reluctant to try the forum - I'm likely to get as many views as respondents! I've not started thinking about double glazing yet - want to sort out under-gunwale first. And, as you say, the moisture-rich air needs somewhere to condense, and I'd rather it did so on the windows than where it can drip onto soft furnishings!

Odet, thank you. Yes, I did wonder whether it was the "extra" cooling the gas pipe gets as the gas expands, but the only use of gas on the boat is for cooking. The wet problem occurred hours after the cooker was last used, so I think it's more likely to be something else. I'll check about the lagging.

Elsie, Dave and Neil, secondary glazing is something I'll consider when I've sorted the under-gunwale issue. Thanks for the tips.

Bruce in Sanity said...


About the gas pipe: easiest thing would be to use the contact form on the BSS site and ask:
You can even upload pix of the situation, which is pretty neat.