Guesstimate on BTU power needed

[trevorbayliss]

I am making an extension which leads off the kitchen. This will be a new lounge. It will be single story with 100mm full fill wall insulation and a 150mm kingspan flat roof. Dimension will be 5.6m x 4.45m x 3.1m. There will be a big 3.5 x 2.3m patio door plus 2 x roof lights 2x1m in size each. These will be triple glazed.

When i have done the BTU calculators most come up with 11000 BTU size needed.

However i wondered how much effect will be the UFH which will be in this new room a little. The area it will run is the back corridor of the kitchen now. This is 4.45m x 1.55m x 3m.

Any ideas on how this heating may reduced down the size of the rad needed for the main new room ?

 

[PrenticeBoyofDerry]

Any ideas on how this heating may reduced down the size of the rad needed for the main new room ?

Simply answer, would be to calculate the output of the UFH in that area and deduct it from you overall calculation.

 

[trevorbayliss]

Well not sure how to calculate the UFH part of it.

 

[PrenticeBoyofDerry]

I would expec it would be designed to give a room temperature of between 18c and 23c.

 

[trevorbayliss]

Well i am thinking a rad giving 8500 BTU will be ok for this room. So a 1400 x 600 double fin rad should be ok. The kitchen is fully open to this room and this has UFH as mentioned, so i guess the two zones will merge in.

 

[Agile]

Heating power has been metricated since 1980.

BTU are an ancient unit from the days of steam power.

kW are so much easier to work with. Just two digits for any rad.

A simple check on power needed is to work out the heat requirement on the floor area. About 0.1 kW psm for a less well insulated and 0.05 kW psm for well insulated.

 

[Dan Robinson]

Tony, why do you jump on people using BTU's when you are totally inconsistent in your own use of conventions and forum rules?

And 100W/m on UFH? Only on screeded floors and tiles with 18mm pipe at 200/150mm centres.

 

[Agile]

I was only quoting what the heating requirement is going to be based on the floor area.

I did not mention UFH.

As you say 100 W/m2 is about the most that UFH can usually deliver. That is why UFH is not very ideal with a poorly insulated house ( like mine ).

Although with my recent new double glazed sash windows it is somewhat better. And much less draughty.

Mine are plastic ( Rehau ) but a friend has just had his house refitted with wooden DG sash windows at huge cost!

 

[Dan Robinson]

I did not mention UFH.

Apologies - you did not.

As you say 100 W/m2 is about the most that UFH can usually deliver. That is why UFH is not very ideal with a poorly insulated house ( like mine ).

It was perfectly fine in my 1910 workman's cottage with solid walls and mickey mouse double glazing. It comes down to the control and the design; but IO agree it certainly not for everywhere.

 

[Agile]

Was that cottage detached?

With the limited heat output of UFH it can take ages to get up to temperature. Once heated it really needs to have heat input all the day, set back a little at night perhaps, to be even usable.

I have also replaced the windows in my 1860 cottage, but when I fit heating that is going to be rads to enable rapid heatup and adequate output.

 

[Dan Robinson]

It was one of those mid terrace with a path splitting the ground floor from the neighbours.

Current house is mid 80's detached with solid concrete floor and no insulation underneath. Rubbish cavity insulation and average, but dated upvc windows. Ufh overlay works very well here too.

 

[trevorbayliss]

I didn't know it was 0.1 KW per sqm. So if i use this calculation, or half it as the extension will be well insulated, and my new room size is 25sqm. Then i need a 2.5 KW rad or a 1.25 if well insulated. So the 1400 x 600 double fin size rad is more than fine for what i need plus a guy is selling a lovely rad for £10 on gumtree so off to get that tomorrow night !