Can't work out how many BTU's my extended room needs

[DIYedboy]

It's a ground floor extension at the rear of my 30's semi. The new bit is 4m out 7metres wide, made from 215mm solid aircrete blocks with 65mm PUR foam thermal plasterboard on dabs on two sides. The party wall is a 100mm block cavity wall with 40mm celotex in the cavity (nextdoor also has built the same extension at the same time. The roof is pitched but I have fitted ceiling joists so I have a flat 8' ceiling with 150mm celotex inbetween the joists. there is a patio door which is 12 feet wide by 7ft high, brand new with argon in the units. there are 2 velux windows in the roof, each is 120cm x 120cm. The floor is suspended timber with 75mm celotex between joists, this new bit is open to the original rear room which is 7metres by 4metres and doesn't have an outside wall and also has 70mm celotex between joists.

sadly the calculation is too trickey for me to work out. Could you tell me how much the new part needs and how much the old part needs (the old bit will be kitchen, the new part will be lounge and dining).

 

[Agile]

I would make a guess of 2.8 kW for the new bit.

For the old bit about 1.4 kW for the old part!


BTUs are an ancient unit from the days of steam!

Since 1980 we have used kW.


As you have a kitchen in the old part then how are you going to ventilate that and introduce make up air?

Tony

 

[45yearsagasman]

BTUs are an ancient unit from the days of steam!

Since 1980 we have used kW

You're wrong again. Rad manufacturers still use Btu's, but hey, what do they know?

 

[oilboffin]

Right again pete.

 

[motorbiking]

Approx 10,000 BTU for the extension. Depending on the flow to the rads and their location I'd over specify by at least 10-20% - The rads must be fitted with TRV any way, so over specifying wont cause a problem. A lot of it will be down to the rate of air change.

 

[Agile]

Rad manufacturers still use Btu's, but hey, what do they know?

Rad manufacturers still quote in BTUs for those dinosaurs who have still not converted their mind even after 36 years!

 

[Agile]

I did a very similar, but larger, room recently.

Used a vertical rad either side of the window at 2.4 kW for the new section.

Then a single one at 2.4 right at the back.

Although in this case the existing part never had the insulation fitted to the floor for some reason!

 

[JohnD]

Radiator manufacturers use BTU because the numbers look bigger.

 

[motorbiking]

The other thing to do is make sure whoever fits the radiator pipes insulates them. In my case my builder was happy to leave 30M+ of uninsulated polypipe in an uninsulated floor void, which I calculated to be the same as having a 5,000btu radiator on the outside of my house. It cost be under £100 to properly insulate them.. Money I'd have lost in the first year if I left it as per the install.

 

[Agile]

Radiator manufacturers use BTU because the numbers look bigger.

That's why I always measure mine in mm.

So 6 inches becomes 150 mm !

 

[Terrywookfit]

Rad manufacturers still quote in BTUs for those dinosaurs who have still not converted their mind even after 36 years!

It will be a cold day in Hell before I retire my Imperial "Mears calculator"!!
When working on older properties it can not be beaten.

A quick calc on my Mears gives me 10200 btu/hr for the new bit.

 

[Terrywookfit]

That's why I always measure mine in mm.

So 6 inches becomes 150 mm !

No s hit Sherlock !!

 

[oilboffin]

What do you measure that's 150mm long sounds rude to me,and a bit short.

 

[45yearsagasman]

That's why I always measure mine in mm.

So 6 inches becomes 150 mm !

Yes Tony, I see what you mean by a little tool.

 

[DIYedboy]

Apologies for not thanking you sooner lads, very grateful to you, I'd have been buggered without your help