It is getting to the stage where I need to start buying some stuff and radiators are one such item. Easy enough I thought but what size radiators do I need? Obviously I will ask our plumber to advise but I do like to understand these things myself if I can.
Radiators are measured in Watts or BTU's (British Thermal Units) and there is a ridiculously complicated system for working out what sizes you need involving the volume of the room, number of outside walls, type of wall (solid, cavity etc), double glazing (yes or no), the aspect of the house (North, South etc), what type of room it is (bedroom, lounge and so on) your inside leg measurement, mother's maiden name and the number of pets you have.
I am convinced that this system has been made sufficiently complex and made to look like a dark art to stop the rest of us from trying to understand it. What makes it worse is that every different method of calculating you use gives a completely different result!
Room volume seems to be the biggest single factor in the calculation with the number of outside walls the room has being another important number. In this respect the house suffers quite badly as every room I need to heat has three outside walls. This seems to add about 40% to the calculation.
Radcalcs gets a lot of recommendation from various websites and is easy to use without being overly simplified. The only problem with this is that in one room it is recommending a radiator with 10,523 BTU's which is a very big radiator in quite a small room.
Ultimately I shall have to go with some common sense but I'll wait and see what the building control officer says during his visit tomorrow about insulation etc before making a decision.
If anybody knows of any other sites with a calculator I would be pleased to hear about it.
Incidentally my calculations state that the bedroom require 6546 and 7469 BTU respectively and the downstairs room will need 7294 and 10523. I know that Tim (see earlier comments) pointed out the downstairs toilet will be cold. Fear not; there will be a an electric towel rail / heater to take the edge off.
Radiators are measured in Watts or BTU's (British Thermal Units) and there is a ridiculously complicated system for working out what sizes you need involving the volume of the room, number of outside walls, type of wall (solid, cavity etc), double glazing (yes or no), the aspect of the house (North, South etc), what type of room it is (bedroom, lounge and so on) your inside leg measurement, mother's maiden name and the number of pets you have.
I am convinced that this system has been made sufficiently complex and made to look like a dark art to stop the rest of us from trying to understand it. What makes it worse is that every different method of calculating you use gives a completely different result!
Room volume seems to be the biggest single factor in the calculation with the number of outside walls the room has being another important number. In this respect the house suffers quite badly as every room I need to heat has three outside walls. This seems to add about 40% to the calculation.
Radcalcs gets a lot of recommendation from various websites and is easy to use without being overly simplified. The only problem with this is that in one room it is recommending a radiator with 10,523 BTU's which is a very big radiator in quite a small room.
Ultimately I shall have to go with some common sense but I'll wait and see what the building control officer says during his visit tomorrow about insulation etc before making a decision.
If anybody knows of any other sites with a calculator I would be pleased to hear about it.
Incidentally my calculations state that the bedroom require 6546 and 7469 BTU respectively and the downstairs room will need 7294 and 10523. I know that Tim (see earlier comments) pointed out the downstairs toilet will be cold. Fear not; there will be a an electric towel rail / heater to take the edge off.
11 comments:
But why have an elec towel rail when they cost 4x as much to run, and are harder to get to turn on and off automatically with the CH? Fit a proper one.
(PS Since you are Decorum, shouldn't your wife be termed Dulce?)
My reading of Treloar says that your 10500 BTU estimate is right, but that insulating the walls brings it down to 6300, or even lower if you use really modern insulation.
I assume 3.5m x 4.3m x 3 m high. Window = 1.8m2, Door = 1.7m2
Temp diff is 22 external, 3 internal
The formula is ventilation plus heat loss.
Vent (w) = m3 x 22 / 2
45 x 22 / 2 = 500
Heat loss (w) = area m2 x temp x U value
Surface loss (w)
Windows and doors (single gl, deduct 48% for dbl):
3.5 x 22 x 5.7 = 440
front wall
7 x 22 x 2 = 310 (*50% if cavity, *25% is insulated cavity)
side walls (each)
13 x 22 x 2 = 570 (ditto)
back wall
10.5 x 3 x 2.2 = 100
ceiling
15 x 3 x 1.7 = 80
floor
15 x 22 x 0.65 (wooden, 0.45 if solid) = 210
Total = 2.8kW (nb 1.45kW is external walls)
Add 15% for heating up allowance = 3.2kW, which is 11000 BTUs
What you need to do is insulate the walls. If you do that to insulated cavity standards, you will need 1.7KW + 15% = 1.95KW = 6640 BTUs, which is a double radiator 600 x 1200 (7083 according to screwfix).
Saving 1.25kw an hour, 6 hours a day, half the year comes to 1350 kw, which is about £80 a year and a lot of carbon. You will get similar savings for the other main rooms, so insulation will pay big time.
Indeed, the Champion insulation guide says that building regs require you to get the U down to 0.35 for walls and 0.25 for the floor. They sell a 30mm insulation that gets to 0.19 - that is a cut of 90% compared with your current walls. (Actis Tri-ISO super 10). "Superquilt" is 16% better, and only 25mm thick. Just using Actis Tri- would reduce the heating demands by 50% for that room - you would need 5400BTU then. All for losing 1" of space! You cut it with scissors, and attach it with a staple gun. Also says, "no need for vapour barrier". It is usually used in lofts, but why not talk to Champion, and building control?
Hope that this is helpful
More than helpful. Thank you very much.
It is interesting to that two different styles of calculator have up with broadly the same figure. It is perhaps worrying though that the on-line style calculators don't take insulation into account. I suspect that the prevalence of over specified radiators is very high as a result. An 11000 BTU radiator is a very large beast.
You are quite right about the building regulations but these guidelines are more geared around new buildings rather than refurbishments. We have to follow a less rigid code but none the less there is an obligation for anyone with a house with three outside walls for every room to do everything they reasonably can bearing in mind practicality and cost.
The reason for going for an electric towel rail for the downstairs cloakroom was to avoid the out and return pipe work that is required bearing in mind it has to run across the top of a solid floor. I think it might be worth re-considering this along with the provision of a 6th radiator in the kitchen.
More calculations to do.
Tim asks “Since you are Decorum, shouldn't your wife be termed Dulce?”
I think I am suffering from a crisis of identity.
You are quite right to have surmised that my name is taken from the Wilfred Owen poem “Dulce et decorum est” however that is decorum not decorum as I have spelt it. There are several websites spelling it the way I have but rather more with the letter u in it. I think I have made the classic mistake of thinking that I remembered it correctly.
This may be quite an apposite post bearing in mind the date today.
Wilfred Owen was anti war but there again - aren't we all?
Here is a link to the full poem http://www.poetryoutloud.org/poems/poem.html?id=175898
Are you declining to describe Mrs D as Dulce? Careful how you answer that one...
You can cut another 200w (680BTU) off my figures for having dbl glazed window and door.
Where is the boiler going to go? remember that you can run CH pipes down the back of the units. If the boiler is above the thin units on the LHS of the kit, you could run pipes to the end of the kit, by the door and have the kit rad there, and the downstairs loo rad by the loo (not perfect, but very simple and better than freezing!)
And you can box them in behind the skirting - that is how our downstairs is done.
nb I still don't know what the big thing next to the cooker is, and if you are ever bored, you could put a scale on your plans, and provide a link to them from the home page.
Looking at the plans again, have you thought about reversing the upstairs loo and basin? I am still concerned that people might have to push past the loo to get to the basin.
"Dulce" means sweet in Italian or Spanish. Presumably from the "It is sweet to die etc..." bit of the poem. I know that part of the poem is Latin but you won't get much closer to Latin than Italian.
Whether Mrs APD would like to be called "sweet" is something I will discover when she has read these comments!
While admiring your demonstrated ability to speak Latin like a native, it occurs to me that you’ll need to know, inter alia, how thick your wall coverings are if your plumber is first fixing before the walls are plastered. Otherwise the pipes leading up to the radiators won’t align with the valves. Similar with electrical sockets.
pleased to see mention of a very large beast
Thank you Wall Observer.
I believe you are suggesting that it will be appropriate to make an adjustment pro-rata to the width of the wall.
I think the plan is to run plastic pipes close to the radiators and then connect coppper L shaped pipes when the radiators are on the wall.
In order to further your latin may I suggest we continue our discussions here http://latinforum.org/viewforum.php?f=19&sid=9e1b8b3dce969a0fe210e6590c1b6184
OK Tim, you win!
I have spoken to the plumber this evening and a radiator is going into the kitchen and a proper towel rail in the downstairs cloakroom.
Excellent. I grew up in a house without heating in bathroom or kitchen. And we had no heating in the bathrooms at college. Believe me, it is not a good idea to have rooms without heat!
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