Heating our bathroom

The bathroom in our old house was cold. Really cold. It had two external, solid brick walls, and the room was tiled floor to ceiling. We had a rubber floor covering, so at least you didn’t suffer from very cold feet.

We had a lot of condensation, which unfortunately led to some mold. We tried to mitigate this by installed a large ceiling extractor fan over the bath, which helped a little, but one of the biggest problems was the radiator – it was just too small.

In our new house, we weren’t going to make the same mistake!

Our plan was two fold; we would install underfloor heating and a towel rail. Our new bathroom has three external walls, but as it’s cavity wall, it won’t be as cold. We aren’t tiling the entire room this time, so the walls shouldn’t be as cold.

How much heat do we need?

The first port of call when trying to determine our heating requirements is a BTU calculator. There are dozens of these online and they use crude bits of information to determine how many watts of heat you will need to warm a space.

I’ve checked a few calculators, putting in three external walls, one window, insulated ceiling and cold floor and got a result of around 1500 watts.

As we had chosen a tiled floor, we decided that we’d use a combination of a towel rail and underfloor heating (UFH). The towel rail to dry our the towels and the UFH to ensure the tiles weren’t too cold in the winter!

Unfloor Heating

We figured that starting with the underfloor heating was the best bet.

UFH comes in two types, wet and electric. Wet involves a series of pipes in the floor that are heated using the central heating. Electric uses a long wire, which gets heated, well, eh, electrically. As we were only heating a small space, the electrical UFH was the better option. It also is pretty easy to install as it doesn’t require a plumber and a complex manifold. This meant I could do it.

There are three parts to electric UFH. First, there is the heating wire. This contains the heating element. Then there is the temperature probe, which measures the temperature of the floor (and optionally the air) and lastly, there is the control unit, which turns the heating wire on and off and regulates the temperature.

The heating element

I found that the heating element comes in two forms. One is a loose wire and the other is a mesh mat, which has the wire attached. When dealing with a really unusual room, the loose wire is recommended, but it’s much more involved in putting it down. The mat, on the other hand, offers an easier solution, but it can be difficult put down when you’re dealing with irregular layouts. You can cut the mat and even remove the wire completely if you want to get into an area where the mat isn’t suitable.

For my bathroom, I was pretty much covering a rectangular area, so the mat made the most sense. They seem to all come with sticky tape, so you can literally just stick them down.

When it comes to these heating elements, it’s worth pointing out that they come in fixed lengths and the wire itself cannot be cut, so it’s impossible to lengthen or shorten it. More on this later!

The temperature probe

This is probably the simplest big. It’s just a long wire with a little bulb at the end. They are usually put into the floor and measure the temperature the floor.

The Controller

The controller turns the heating on and off to keep the room at the desired temperature. As I’m a smart home nut, I wanted to have some ability to control and manage this remotely, so I opted for a Heatmiser neoStat-e V2. This unit is designed for electric UFH and supports 16A mat (way more than I’d need). Heatmiser units can also be connected to an optional hub for remote control. Whilst I may never connect it up, it’s nice to have the option.

The controllers all seem to come with a temperature probe, probably because they are calibrated for them.

Getting Started

I started by drawing out the bathroom floor and blocking out where the shower, bath and toilet would be. These occupy floor space, so heating them made no sense.

My plan to lay out to mat

I figured I needed to cover approx 3sq/m. You have to leave 10cm gap between the mat and any walls etc.

We knew that the towel radiators would offer between 600 and 1000 watts of heat, so I then choose a mat which provided 200 watts per square metre. A total of 600W.

The mat I bought was a ProWarm model and I got it from https://www.theunderfloorheatingstore.com/

When the mat arrived, however, it was for 3.5 square metres!! The mat is 50cm wide, so this equated to an extra meter of mat, which was going to be lots of extra wire. Initially I panicked, but then my bother-in-law pointed out that I can simply cut the wire off the mat and lay it down any way I want. I looked at my floor layout again and decided it would work and I could just heat heat either side of the toilet. An extra 100W of heat for free!

The electrician got the important part setup for me, with a fused spur and 35mm backing box for the controller.

The electrics outside the bathroom
The final arrangement with power running from the fused spur up to the box where the controller will live.

The white conduit holds the mat’s power cable and the temperature probe. Heatmiser recommend that the probe can be accessed and removed in the event it fails. I used the white conduit down the floor and then a 7mm flexible black conduit, which would under the tiles.

Electrician added outlet for radiator and I took the UFH wires through the same spot
I stuck the conduit down to test how easy it would be to remove and reinsert the probe.

To test this setup would work, I stuck the black conduit down to the floor to simulate it being in position in the finished floor. I think removed and replaces the probe twice. It was pretty easy and just required a little pressure to get it moving. In the event the temperature probe did fail, I had *some* hope of being able to replace it.

The next step was to put down concrete backing boards on top of the floorboards. The builder recommended this as it would reduce movement in the floor and prevent the tiles from cracking.

The concrete backing board on top of the existing floorboards

At this point, I was very conscious of what the finished floor level would be. The backing board, the mat and then the tiles. One problem at a time.

The tiler, who was going to put down the self levelling layer over the mat asked me to make sure there were no gaps around the edges of the room. He said the liquid would simply pour through the holes making his job very difficult. To tackle this, I used a mixture of expanding foam for the larger gaps and decorators caulk for the smaller gaps.

Foam to seal the edges
Caulk in the joints of the backing board

I also put caulk into the joints of the backer board. Belt and braces.

Next, I had to cut a whole in the floor and locate the bath waste. The plumber had left a mark on the subfloor, which *thankfully* I had photographed!!

Some masking tape and a distance from the wall

The multitool came in handy, yet again. I marked out the positions and cut the backer board….

X marks the spot!
The moment of truth!

With the bath waste hole cut, I turned my attention to the heating mat. I’m not going to lie. This really, really frustrated me.

My mistake was not understanding that the mat could be laid either side up. I had initially unrolled it thinking the tape strips (for sticking it down) were on the bottom; which they weren’t. I had already cut the mat when I realised this, so I flipped the mat over and carried on. When I’d unrolled it, the extra amount was *way* more than the 1m I was expecting. It was closer to 1.25m

Long story short, after much cutting and thinking (99th percentile for spatial reasoning at age 17) I had it down.

Better coverage than I expected

It’s a little rough, but I got better coverage than I expected. Once it’s stuck down and covered with the self levelling stuff, nobody will know except me, my wife and the tiler. And you, dear reader.

Next job was to sink the wires and temperature probe, so they didn’t stand proud above the mat. I marked it all out and using the multitool, I cut grooves for the power wire and probe conduit. I think used a chisel to cut out the groove.

It was slow work, but I got there in the end. Of course, by cutting through the backing board, I’d added an break in the mat, but hopefully this wont’ introduce any more movement.

The temperature probe in position. It’s curved to take it closer to a heating wire.
I taped down the mat to ensure it didn’t stick up too much

You can see along the shower tray that I cut the wire away from the backing mat and just stuck it down, ensuring I left spacing between he wires. The tiler then came and put down the self levelling. I was initially going to do this myself, but I reason that the tiler would be much happier working off a surface he was responsible for, rather than my amateur effort.

The self levelling compound in place! You can see a few places where the mat pokes out about the surface

After 24 hours, the floor was ready to walk on. I checked the resistance of the mat and temperature probe for the umpteenth time and all was good. The tiler then set to work.

The fabulous tiles my wife picked out!

The Radiator

Not much to say here as you probably know what a radiator is. Powered by your central heating, this is the most common way of heating a bathroom. This time around, we also wanted to install a dual fuel radiator.

What is Dual Fuel?

As towel radiators are connected to the central heating, you are guaranteed of a nice warm, dry towel during the winter months, but once you get into the summer, the radiator is never hot. This can leave towels damp and lead to excessive moisture issues.

During the course of my research into moisture issues in my previous bathroom, I discovered something called Dual Fuel radiators. Essentially, you can install an electric heating element into the radiator, so that during months when the central heating is off, the radiator can be heating up electrically!

The operation of the element requires a manual step where you essentially switch from water heat to electrical heat. In the spring, once the central heating is off, you need to shut the radiator valves and open the little “bleeded” valve at the top. You can then turn on the electric element. In the autumn, when it’s time to switch back, you operate in reverse.

Things, however, turned out to be a little tricky when it came to the dual fuel element. Regulations here in the UK, have strict rules about electrical items and water and dual fuel elements are governed by this rules. Anything electrical typically has to be 60cm away from the edges of showers, baths or sinks. We confirmed this with our electrician just to be sure.

Sizing it

With 700W coming from the floor, We only needed 800W to make up the difference. The output of a radiator is measured in two ways – BTUs and Watts. The output also depends on the temperature of the water running through the system and the temperature difference between the radiator and the room it’s heating.

We also only had 75cm of space on which to hang the radiator and we had to allow at least 10cm for the spur.

We needed something that was around 500mm wide, black, not too tall, output at least 800W and supported dual fuel. We’d left it quite late to order a radiator, so our options weren’t actually that large. I found something, which suited our needs perfectly and was able to get it delivered within a week.

We ended up with a Radox Hercules. A good strong name for a radiator. I ordered it from Designer Radiator Concepts. There was some confusion around delivery date, but we were able to get it within a couple of days. They provided the valves and dual fuel kit.

When the plumber came to hang the radiator we discovered that a part was missing – the t-piece. This mean the plumber couldn’t position the tails (a fancy way of saying pipes) of the radiator correctly. He fixed the value on one side, but not the other.

The rad on the wall. It looks really nice. Ignore the pipework.

The layout worked out very well. The plumber was able to hand the radiator, centered on the wall. By placing the valve under the radiator as opposed to outside (which I hadn’t even thought of), the rad size worked perfectly!

Backing box for spur in relation to the radiator. Perfect!

Unfortunately, a large lump of plaster fell off the wall when the electrician was trying to cut out the box. Once I had positioned the mat’s wire and probe, I used some bonding to stick a lump of plasterboard into position.

Fixing the wall

Next steps

Once the first fix is finished and the radiator plumbed in correctly, I’ll write up another post covering the setup and control of the underfloor heating and go into some depth on my plans to control the dual fuel element using a Shelly 1 relay.

Stay tuned!

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