Radiators Cals - Do these seem correct.

ryanneil · 21 Dec 2010

Hi.

I used the Kermi calculator to work out the following calcs.
First Floor Apartment.
Attic above, 300mm insulation.
Non insulated concrete follow assumed temp of 10c.
Non insulated cavity walls.
External walls factored into tool.

Not factored in is the fact site is very exposed and north facing. Would you recommend adding ten or twenty percent for a very exposed north facing room.

Not sure if the calcs I receive too high. The reason I ask is that the bedroom which it has reported as requiring 7291 btus was left on full over night at full power even when it was - 5 outside.

Sitting Room: 6.6 x 5.5 x 2.5 meters. Windows: 5.7m. 17300 btu
Bedroom: 3.4 x 4.5 x2.5. Windows: 2.05m. 7291 btu
Bedroom: 2.8 x 3.5 x 2.5 Windows: 2.95m. 2330 btu
Bathroom: 1.8 x 2.0 x 2.5 Windows: None. 1750 bt
Hall: 0.96 x 6.6 x2.4 Windows: None. 1355btu

Any help would be much appreciated.

Thanks

75pete · 22 Dec 2010

have a look at inspiredheating .co.uk/radiators

ryanneil · 22 Dec 2010

Thanks for the link, even more confused now

Some come out spot on others are a mile off. Maybe I will just over size by 20% and add trvs

Diyisfun · 22 Dec 2010

Add try's, much easier to get each room at correct temp as long as the rad is man enough.

D_Hailsham · 22 Dec 2010

Have you tried using the Boiler Size Calculator? It does not do a room by room calculation, but it will tell you if you are in the correct ballpark. Deduct 2kW from the boiler calculator result to give the Heating requirement.

The only calculators I know of which take orientation and exposure into account are the expensive ones used when calculating the SAP rating of a house.

ryanneil · 22 Dec 2010

Thanks. Getting 9.18 when I remove the 2kw for hot water. So 31345 BTUs. Quite intresting as the Kermi rad cals are within 5% of the boiler sizing calc. Should I be allowing extra for the fact the apartment is on an exposed site with no shelter on any side at all. Completly open to wind and rain on all sides with open land to everyside. Single building in now a green belt/park.

Thanks again all for the replies so far.

ryanneil · 22 Dec 2010

Just one thing, I know you guys get a lot of requests on here for rad sizing, perhaps it is a good idea to as you advised myself to tell people to do a room by room calc using say Kermi and a Boiler sizing, the double book keeping of rad sizing, the fact the boiler sizing and kermi have matched up so closly really helps clould out any doubt. Now only need to figure in if I need to add extra as im on an exposed site with two northly facing sides.

damn little details. That 20% extra and trvs sounds good

once again.

D_Hailsham · 22 Dec 2010

ryanneil said:
Now only need to figure in if I need to add extra as im on an exposed site with two northly facing sides.

Most calculators already include 10% extra, mainly to allow for heat loss in the pipes and to provide a faster warming up time. It also allows for the times when the outside temperature is lower than the standard -1C; but not as low as some have been experiencing recently!

I would oversize the boiler by another 10%. How you oversize the rads could be done on a room by room basis; e.g. those on the north side by say 20%, and those on the south side not oversized at all - as long as the rad total does not exceed the boiler output.

Using two calculators is a good way of confirming your initial findings. The important thing is that you use the same data each time as many online calculators make assumptions about the construction of a house.

ryanneil · 22 Dec 2010

Thanks for the tips re over sizing, the boiler is a 24kw combi so is well over sized, as the largest room is also the north facing one and has three windows 20% sounds a good idea. I set the outside design temp to -3 to all for this cold spell becomming a annual event. For those who want to know I used the Kermi calculator and the boiler sizing tool linked above here. I think I will add another ten percent to the other rad sizes to allow for the apartment below my own being empty and the fact they also rarley use their heating, as everyone here says better too big with trvs than too small altogether.

diynot

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Radiators Cals - Do these seem correct.

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