question on Central heating

[ashfordtown]

I am looking to replace/upgrade our central heating system, at the moment we have a Baxi back boiler thats about 30 years old, I intend to replace this with a condensing boiler in the kitchen,not a combi as we want to keep the cold water tank in the loft, mains cold water pressure is terrible in the summer and we want to keep the power shower.

I have worked out the BTU needed for the new radiators as about 70,000 btu, I was looking to have the feed and return on the first half of the system 28mm pipe feeding the bedroom rads and going down to 22mm to feed the living room etc, am I being overkill by using 28mm ? I assume the bigger the pipe the better the flow. Do the boilers have 28mm (1") outlets. Would appreciate any comments on my idea.

Steve

 

[clf-gas]

22mm will serfice

 

[gas4you]

As you will probably be upgrading to a fully pumped system from the age of your present one, I would recommend running 28mm from the boiler flow and return to the airing cupboard where the cylinder is then after pump and 3 port or 2 port valves reduce down to 22mm for each circuit.

Just use a 28mm-22mm reducer straight off the boiler flow & return.

This will ensure a fast heat up of system and will future proof against any additions you may make later.

I always use 22mm up to a max demand of 60,000 btu

 

[Bambergaspipe]

I am looking to replace/upgrade our central heating system, at the moment we have a Baxi back boiler thats about 30 years old, I intend to replace this with a condensing boiler in the kitchen,not a combi as we want to keep the cold water tank in the loft, mains cold water pressure is terrible in the summer and we want to keep the power shower.

I have worked out the BTU needed for the new radiators as about 70,000 btu, I was looking to have the feed and return on the first half of the system 28mm pipe feeding the bedroom rads and going down to 22mm to feed the living room etc, am I being overkill by using 28mm ? I assume the bigger the pipe the better the flow. Do the boilers have 28mm (1") outlets. Would appreciate any comments on my idea.

Steve

You`re gonna lose your gas fire if you upgrade you need 22mm pipes from your new boiler, any drops in 15mm (some may argue 10mm), not for me it`s prone to blockage.

 

[Bambergaspipe]

As you will probably be upgrading to a fully pumped system from the age of your present one, I would recommend running 28mm from the boiler flow and return to the airing cupboard where the cylinder is then after pump and 3 port or 2 port valves reduce down to 22mm for each circuit.

Just use a 28mm-22mm reducer straight off the boiler flow & return.

This will ensure a fast heat up of system and will future proof against any additions you may make later.

I always use 22mm up to a max demand of 60,000 btu

Absolutely no point in doing this, once your system is fully pumped you will only need 22mm pipework, you will get away with smaller but I would stick with 22mm as for faster heat up times because you have a bigger bore of pipe is rubbish.

 

[gas4you]

Each to his own. Water flow through pipes should only flow a specific rates for each pipe size, can't remember what they are off hand. In theory text book says about 45,000 btu for 22mm.

For how little 28mm will cost extra on the entire job one would be foolish not to do the job properly in the first place.

Why don't you use 15mm everywhere then , this will still get everything hot but take a few hours to do so.

 

[Bambergaspipe]

Each to his own. Water flow through pipes should only flow a specific rates for each pipe size, can't remember what they are off hand. In theory text book says about 45,000 btu for 22mm.

For how little 28mm will cost extra on the entire job one would be foolish not to do the job properly in the first place.

Why don't you use 15mm everywhere then , this will still get everything hot but take a few hours to do so.

It won`t m8, it will get hot nearly instantaneous in a normal 3/4 bed house, unless he lives ina 30 bed mansion 28mm is normally reserved for gravity fed systems or pretty huge gaffs . He`s whacking a boiler in the kitchen for Gawds sake

 

[Rob]

22mm can only carry so much, i always thought was around 60,000btu. So anymore is a waste.

Although this is usually plenty for 3 bed house.

 

[Balenza]

gas4you wrote

Each to his own. Water flow through pipes should only flow a specific rates for each pipe size, can't remember what they are off hand. In theory text book says about 45,000 btu for 22mm.

For how little 28mm will cost extra on the entire job one would be foolish not to do the job properly in the first place.

11C Temperature Difference Between Flow and Return
(81C flow - 70C return) Non-Condensing Boilers

Pipe size - Output in kW
15mm - 6.0 kW
22mm - 13.4 kW
28mm - 22.5 kW

20C Temperature Difference Between Flow and Return (70C flow - 50C return) Condensing boilers

Pipe size - Output in kW
15mm - 9 kW
22mm - 24 kW
28mm - 70 kW

The condensing boiler can use 22mm pipe where 28mm would be required for a non-condensing boiler.

The wider the delta T the more heat is being transferred, so smaller pipes - condensers shine here, as installation can be cheaper eliminating 28mm pipe in most cases.

A shame most don't know.
And incidentally my 90,000btu non-condensing oil boiler has 22mm f&r pipes and no problems.

 

[Agile]

I think you may have mistaken over the heat required.

First most BBUs are only 8-12kW output.

70,000 is about 21 kW !!!

A typical three bed house requires about 10-12 kW. This is adequately supplied with 22 mm flow and return.

Is yours really a large six bedroom detached house? If so how on earth has your little BBU been heating it adequately?

Tony

 

[Bambergaspipe]

gas4you wrote

Each to his own. Water flow through pipes should only flow a specific rates for each pipe size, can't remember what they are off hand. In theory text book says about 45,000 btu for 22mm.

For how little 28mm will cost extra on the entire job one would be foolish not to do the job properly in the first place.

11C Temperature Difference Between Flow and Return
(81C flow - 70C return) Non-Condensing Boilers

Pipe size - Output in kW
15mm - 6.0 kW
22mm - 13.4 kW
28mm - 22.5 kW

20C Temperature Difference Between Flow and Return (70C flow - 50C return) Condensing boilers

Pipe size - Output in kW
15mm - 9 kW
22mm - 24 kW
28mm - 70 kW

The condensing boiler can use 22mm pipe where 28mm would be required for a non-condensing boiler.

The wider the delta T the more heat is being transferred, so smaller pipes - condensers shine here, as installation can be cheaper eliminating 28mm pipe in most cases.

A shame most don't know.

Beautiful figures, a shame you are talking through your ***. Next time you install a boiler (improbable) take the time to measure the Flow & Return temps, if you get the magic 56 degrees diff erence on the return to make the boiler really condense I will show my *** in Woolworth`s.

 

[Balenza]

Agile wrote

A typical three bed house requires about 10-12 kW.

Can you define typical ?
The bedrooms must be about 10 sq feet in these homes.!

 

[Balenza]

gas4you wrote

Each to his own. Water flow through pipes should only flow a specific rates for each pipe size, can't remember what they are off hand. In theory text book says about 45,000 btu for 22mm.

For how little 28mm will cost extra on the entire job one would be foolish not to do the job properly in the first place.

11C Temperature Difference Between Flow and Return
(81C flow - 70C return) Non-Condensing Boilers

Pipe size - Output in kW
15mm - 6.0 kW
22mm - 13.4 kW
28mm - 22.5 kW

20C Temperature Difference Between Flow and Return (70C flow - 50C return) Condensing boilers

Pipe size - Output in kW
15mm - 9 kW
22mm - 24 kW
28mm - 70 kW

The condensing boiler can use 22mm pipe where 28mm would be required for a non-condensing boiler.

The wider the delta T the more heat is being transferred, so smaller pipes - condensers shine here, as installation can be cheaper eliminating 28mm pipe in most cases.

A shame most don't know.

Beautiful figures, a shame you are talking through your ***. Next time you install a boiler (improbable) take the time to measure the Flow & Return temps, if you get the magic 56 degrees diff erence on the return to make the boiler really condense I will show my *** in Woolworth`s.

Not mine . Just stating my findings.

 

[Agile]

[
Beautiful figures, a shame you are talking through your ***. Next time you install a boiler (improbable) take the time to measure the Flow & Return temps, if you get the magic 56 degrees diff erence on the return to make the boiler really condense I will show my *** in Woolworth`s.

I think you are getting confused by the differential temperature of the flow and return and the simple return temperature!

The return needs to be about 55°C to get much conddensing.

Tony

 

[Bambergaspipe]

Not mine you Just stating my findings.

What does that mean? not really an answer was it? if you are going to just paste figures from a text book, please have the **** to back them up,