Hello there
What dimension / BTU of heated towel rail (working off the centra heating) would be recommended to heat a small bathroom? There will b no other heater in the room. Any factors anyone can think of of whic I should be aware
-- Totally clueless
How long is a piece of string? How small is small? Big windows? Solid brick walls or cavities? etc. etc.
Towel rails are not a good sole source of heat for a bathroom anyway because their output is small to begin with.
Cover them with a nice insulating layer of towels and the output reduces even further.
You need to workout the heat loss for the bathroom, any other way will be guesswork. If you are going to guess, then fit the biggest you can!
(google this group (uk.d-i-y) for working out heatloss)
On Wed, 30 May 2007 16:31:18 +0100 someone who may be Totally clueless wrote this:-
A room with a bath is not small. A heated towel rail will not heat such a room unless it has a radiator in the middle or the room is in a highly insulated house (and even in such a house the necessary ventilation means the towel rail may not be sufficient).
A small radiator is a better bet.
Search the group. However, being able to operate the rail separate from the radiators is very useful.
Here are a pair of examples; Shower /toilet in modern extension - nominally 5ft square; kept just warm with an electric towel rail which is 33" high and 21" wide and has 3 rails in it (similar looking Screwfix example is 130w)). Additional fan heater on the wall - necessary in the winter. One average size DG window
Bathroom - original 3ft thick stone walls with insulated lining, one small single glazed window, north facing. 12' x 6' . CH radiator estimated output 500w keeps the room comfortable. SWMBO had me fit a fan heater but it is rarely used.
Typical height ceilings are fully insulated. We're near Edinburgh.
Rob
If its insulated well (the room) a couple of hundred watts is enough.
>
It can be.
Bollocks
It is.
sure, but its ugly, and you can't hang towels on it.
That is true.
>
As long as you don't cover it with towels... which is easily done on the smaller rails.
I found with the one in my loft shower room[1] (room 6x7' ish, smothered in PIR foam insualtion - 100 to 130mm in outside walls, 100mm on inside, one dg window 20mm gap, argon fill etc), that the rads nominal 400W or so is adequate when uncovered, but if you throw a couple of towels on it carelessly it gets chilly in there.
[1] this one:On Thu, 31 May 2007 09:42:30 +0100 someone who may be The Natural Philosopher wrote this:-
That depends on what one means by small.
A room with a bath, even if has just has a bath, will be roughly twice as big as a room with a toilet and basin. A room with a toilet and basin can be heated by a towel rail, in the circumstances I outlined, a room with a bath cannot.
Ah, proof by assertion. The calculations are easy enough to do and I have done them often enough to know what is what.
Not every house is well insulated. You appear to be talking about a specific instance, I am talking in general. Given that the OP did not state how the house is constructed I suggest it is best to stick with the general.
No more ugly than any other radiator.
It is much better to hang them on the towel rail.
On Thu, 31 May 2007 10:43:52 +0100 someone who may be John Rumm wrote this:-
If one throws towels on it with care is it adequate:-)
On 31 May 2007 01:16:09 -0700 someone who may be robgraham wrote this:-
Supplementary infra-red heaters are far better in bathrooms, which tend to have a high ventilation rates. They also give a genuine olde worlde feel.
Really? Even without the size of the room as input data?
You must be very clever.
Yes.... sort of 1950s olde worlde. Lovely.
Mine is.
well so have I.
A typical bathroom with sensible U values and only one or two outside walls needs 200-400W at most. Well within a decent towel rail.
"There is nothing more useless than a general maxim"
A single storey single brick extension bathroom, with three outside walls, a ceiling and a floor all uninsulated, will vary by a factor of around 40:1 compared with a bathroom upstairs under decent loft insulation with street legal isnulation to only one outside wall.
Somewhere between 100W and 4KW. rewquired. YOU tell me what the GENERAL case is.
I have had and used bathrooms that coonformed to both those criteria. Chalk and cheese.
So hea the towel rail and save space.
Far better to run a few uninsulated hot water pipes under the floor.
On Thu, 31 May 2007 11:37:43 +0100 someone who may be The Natural Philosopher wrote this:-
Yours is what? Roughly twice as big as a room with just a toilet? Heated by a towel rail in the circumstances I outlined?
Ah, "sensible" U-values and only one or two outside walls.
Whether that amount of heat is desirable just to dry towels in summer is debatable. 100W or perhaps 150W tends to be enough to dry towels. Far better to separate drying towels from heating the room. The towel rail heat input can be added to that of the heating system and if it is enough to keep the room warm the radiator will turn itself off via a thermostatic valve.
Oddly, that *is* the point I was making.
With our small rail, if you drop a bath towel right over it then you reduce its output to near enough nil. Thread it through the slats so that a couple of the top rails are clear, along with the uprights and it will still dump enough heat into the room. Its not so much of an issue with bigger rails since it is harder to lose them under one big towel.
The room is 2.4 long x 2.8 high by 1.4 wide (one of these short wall
faces onto the unheated common stairwell of the Edinburgh tenamen block where I live). There is no window. The flat is from 188 approx, and the walls of it are brick (the outside of the block i stone).
Sorry I didn't give all of these details beforehand - I'm very muc learning as I go....
Thanks for all your help to date - any further thoughts as to whether towel rail would be sufficient by itself, and the BTU you'd recommend ( don't think I can use watts - it will be running off the combi boiler would be much appreciated. I'm aware that the BTU calculator indicate
1500-1800 - what do you think of this? Too much? Too little?I'm a hardy lass, living way up here in Edinburgh, but I don't want t freeze my a*se off
-- Totally clueless
This isn't going to have the lowest heat loss possible :-)
It's better not to mix units. The conversion between Watts and BTUs/hr is 3.413, so 1500 BTU/hr is 439 W and 1800 is 527W.
Basically, the heat required to maintain the temperature of a room is whatever is needed to compensate for the heat loss which will be through walls, ceiling, floor and air changes.
These are calculated by measuring the surface (e.g. the large wall is
6.72 sq. metres), multiplying by the temperature difference (e.g. you would like 22 degrees in the bathroom when it's -3 outside, so a 25 degree difference) and multiplying again by a factor (called U value) which depends on the construction of the surface. This gives a figure in watts. Repeat for all surfaces. There is a similar calculation for heat required to warm the air because of air changes. Bathrooms are normally reckoned on at least two air changes per hour because of the required ventilation. All of the figures are then added together and this tells you what the radiator needs to actually deliver to achieve the temperature you wanted.If the radiator is too small, then the room will be cooler, easy as that.
I don't have the tables in front of me for the walls, but I would estimate that the amount of heat from a towel radiator of this size is not going to do too much more than take the chill of of the room.
There is an effect called thermal mass which is basically the heat storage effect of the walls. In a place with substantial brick and stone, this becomes significant. The good news is that that tends to retain heat. The bad news is that is takes time to warm up. This suggests that having the towel rail running as much as possible will be a good solution when the weather is cold.
OK to work out the heatloss you need to know:
1) the area of each surface (i.e. walls, floor, ceilings, windows). 2) You need to know the u value for the material each wall etc is made from (this is a figure that tells you how good or bad the material is at passing heat). 3) You then need to know the anticipated worst case temperature difference from one side of the surface to another. (The heatloss through a wall that is a really poor insulator, will still be nil if both sides are at a steady 20 degrees) 4) Finally you add in a fiddle factor based on how often the air in the room is "changed".Well for the sake of argument you could treat the walls as if they were
9" solid brick.Some u values for you:
Wall - outer 9" solid brick 2.2 Wall - internal plaster over 4" block 1.2 Wall - internal PB over stud 1.8 Floor (ground) - solid concrete 0.8 Floor - PB + joist + FB flow up 1.9 Floor - PB + joist + FB flow down 1.5 Roof pitched with felt + 100 insulation 0.3 Window - wood DG 2.9 Window - wood - low E 1.7 Door single glaze 3 Wall Insulated 0.6
So you have two walls of 2.4 x 2.8m = 6.72m^2 and two of 1.2 x 2.8 = 3.36m^2 and a floor and ceiling of 2.4 x 1.2 = 2.88m^2
So lets say wall 1 is one of the big ones. Its made of plaster over block construction, and you have a room the other side of it that is typically 3 degrees C cooler than the bathroom. The heatloss through that wall would be:
6.72 x 3 x 1.2 = 24WFor your wall onto the unheated stairwell, the worst case temp difference might be much more - say 18 degrees So you get:
3.36 x 18 x 1.2 = 73Wnow repeat for the other walls, and the floor and ceiling. Note that it is possible to get negative heat loss through a wall, i.e. gain from a warmer room next door.
Add up the total. That is the basic heatloss for the room. Now add a fiddle for air changes:
Typical room temps and air changes:
Room type Room temp Air Changes Lounge 21 1 Dining Room 21 2 Bedroom 18 0.5 Hall and Landing16 1.5 Bathroom 22 2 Kitchen 18 2
To do the air change bit you multiply the volume of the room by the air change factor by the temp difference between the warm air in the room, and the air you are exchanging with. So if most of the ventilation is to the outside you would take a bigger temperature, than if its all into the house.
The room volume is 1.2 x 2.4 x 2.8 = 8 m^3
So say your bathroom came to 500W of loss, and the air is being exchanged into the hall which you keep 6 degrees cooler than the bathroom. You get:
8 x 6 x 2 = 96WAdd that to the first total, and you know know what power radiator you need to keep up with the losses of the room.
If all your walls bar one are internal, and there are heated appartments above and below you, your loss should be quite low and it may cope. However you need to do the sums to find out.
1 watt is equal to 3.4 BTU/hour...Type this search into google: "1800 british thermal units per hour in watts" and it says 527.5W
In the range of a biggish towel rad if you don't smother it with towels.
Blue is never a good colour for an arse!
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