Is My Electomax boiler undersized?

[andysmif]

I have recently bought a newly converted flat. The boiler that is installed is a Heatrae Sadia Electromax 9kW. This powers a wet heating system but whenever the central heating is on the boiler runs at full power continuously. I think the boiler is undersized for the 5 single panel and 2 double panel radiators that I have but I need some calculations to go back to the builder with in order to get this problem sorted. Any ideas?
Thanks

 

[ianmcd]

you will have to measure the sizes of the radiators to see what their KW rating is but I would doubt from the information you have given whether the boiler at 9KW would be undersized I have fitted that size boiler with more rads than that

 

[andysmif]

The double radiators are:
120cm x 60cm
80cm x 60cm

Single:
50cm x 60cm
40cm x 60cm
3 at 100cm x 60cm

 

[JohnD]

as a rule of thumb, a single radiator 600mm high uses about 1kW per linear metre of rad. A double rad about 1.8kW. These figures are a bit generous as they are calculated at optimal conditions. the lower the water temperature, the less energy the rads can disperse. It looks to me like your rads and your boiler are about right. If you have TRVs, the load will drop as the house warms up and the rads turn down. What temperature do you set the thermostat to?

If you have a HW cylinder it will draw some while going from cold to hot, but if well insulated, will only lose about 2kWh per day, but if you keep running baths or it is badly insulated, then it will keep drawing heat.

Does your boiler have a buffer tank?

Are you in a top-floor flat, or a corner one with several outside walls?
Or are you in a ground-floor flat with no carpet?

A conversion in an old building might have quite poor energy performance. We don't know how big it is or how well insulated, or if you ran your test in cold weather.

see examples:
http://www.screwfix.com/p/kudox-pre...ingle-convector-radiator-white-600x1000/36126

http://www.screwfix.com/p/kudox-pre...ouble-convector-radiator-white-600x1000/65888

 

[andysmif]

The flat is split over 2 floors. The top floor being in the roof with noone above and all four sides meeting the external walls. The ground floor of my Flat has 2 walls meeting the external walls and unoccupied flats to the sides and unnoccupied offices below. It is converted from quite an old old building. The living room has a large bay window made up of 3 sash windows. They are not very well insualted and let draught through. I do have some curtains to cover but they are not as thick as I'd like them to be. The ceilings are almost 3m high as well so a lot of space to heat. The HW comes from the boiler as well but it seems to last a long time once its heated up. I did have the thermostat set at 20 degrees but it hardly ever reached this temperature causing the boiler to run at full power continuously and then trip its fuse in the fuse box. I had the heating on for 2 hours in the morning and 2 in the evening and it was costing me around £50 a week. I now only have one radiator on for an hour a day.

 

[JohnD]

if it's an old building (you mean prior to 1930?) then the wall are probably solid, no cavity, lose a lot of heat unless they have drylining with insulation.

the roof rooms ought to have been well insulated with mineral wool all round. See if they are.

When the rest of the building is occupied and heated, your flat will get warmer.

Buy draught-strip for your windows. It sticks well to clean new paint. Get the EDPM E-section or P-section, not cheap foam strip.

edit
for sliding windows, use the furry brush pile draught strip. It is more expensive but will give better performance and allow the windows to slide.

 

[ianmcd]

If you have a HW cylinder it will draw some while going from cold to hot, but if well insulated, will only lose about 2kWh per day, but if you keep running baths or it is badly insulated, then it will keep drawing heat.


The Electromax has a built in stainless steel highly insulated cylinder you dont need to worry about this

 

[andysmif]

Thanks Everyone

The building is a listed building and yes I think it's pre 1930's. If the walls are therefore solid, is there anything I can do to reduce heat loss through them? I'm looking into getting the windows replaced with replica double glazed sash windows but my wallet doesn't yet stretch to about 4k!

 

[JohnD]

cheap and quick for this winter, you could apply the plastic film over the windows. You could insulate the walls better by drylining with an insulating layer. But start with the loft insulation and any walls inside the roof as that will be cheapest and not disruptive.

You might also consider Secondary Glazing, which retains the original windows. It is also better for soundproofing than DG.