SYSTEM SIZES

[chrisw1]

Hello,

I have a Victorian semi currently with electric panel heating. A £3,000 catch up electric bill has motivated me to install GCH but cost is a major factor for us.

I am thinking of purchasing the system and getting the pipes and rads ready for a qualified engineer to connect all and test.

I calculated that I need 40,000 BTU for downstairs and I believe that means I need 28mm piping as the limit on 22mm is 36,630.

All the TRV's for rads are 15mm so I can't see how 28mm will connect.

Would I just use a standard reducer from the 28mm pipe and connect to the rad with standard 15mm pipe? This seems daft if 15mm pipe is limited to 13,620 BTU when one of the rads is 5,500 BTU - surely it wouldn't be heating to its potential and I may as well stick in a smaller cheaper rad and sit there cold!

All suggestions welcomed.

Thanks in anticipation.

 

[chrisw1]

SORRY-

I've also calculated that I need a boiler capable of 19Kw.

I've seen one that states its output is 10.9 - 24.9Kw.

Do I go with the minimum or maximum?

 

[D_Hailsham]

I am thinking of purchasing the system and getting the pipes and rads ready for a qualified engineer to connect all and test.

Not a good idea.

1. The installer will be able to purchase the parts cheaper than you
2. If any parts are missing or faulty the problem will be yours, not the installers.
3. The installer will not give you any guarantee. So, if the something goes wrong with the boiler six months down the line, you will have to call the boiler manufacturers service engineer and if they find the fault is caused by an incorrect installation, you will have to bear the cost of remedying the problem.

I calculated that I need 40,000 BTU for downstairs and I believe that means I need 28mm piping as the limit on 22mm is 36,630.

What did you use to calculate the requirement? My guess is an online room-by-room calculator (BTU gives it away - kilowatts are used now)

Use the Boiler Size Calculator. As you have a semi, there are two walls side-to-side and one wall front-to-back.

All the TRV's for rads are 15mm so I can't see how 28mm will connect.

The 28mm, if needed is used for the main ring. Rads are connected in 15mm to the ring using 28/15 tee couplers. If you don't understand this, I think you will have considerable problems designing the system.

Read SmallBore heating Systems and Copper Tubes in Domestic Heating Systems

 

[mysteryman]

One of the best boiler manufacturers has 35kW boilers with 22mm connections. A competent installer will know what is needed.

 

[chrisw1]

Thanks for the responses.

I calculated in both BTU's and Watts and also used the boiler size calculator.

I just don't get how a 15mm pipe can adequately seve a radiator larger than 4250 Watts / 13620 BTU.

According to:

http://www.diydata.com/planning/ch_design/limiting_factors.php

the diameter of the pipe restricts the radiator. If you use a reducer from 22mm to 15mm then surely the radiator is limited to the 15mm feed?

Isn't it like a motorway going into a single carriageway?

 

[D_Hailsham]

I just don't get how a 15mm pipe can adequately serve a radiator larger than 4250 Watts / 13620 BTU.

You haven't read the first reference I gave you, have you?

For an 11C difference and a speed of 0.9m/sec the capacity of 15mm pipe is 6kW. I don't see where your ref gets 4.25kW from; the figure of 1.4W/litre is meaningless.

If you use a reducer from 22mm to 15mm then surely the radiator is limited to the 15mm feed?

If the 15mm was feeding into 22mm there would be a problem, but it's the other way round. The 22mm pipe will be carrying the flow for more than one radiator. Just as the motorway is carrying more traffic than the roads connected to it.

And you haven't read the second reference I gave!. This explains how you should size all the pipework on a system. However there is a reluctance by many installers to use sizes smaller than 15mm, even if they would be more appropriate for the required flow.