correct temperature setting for gas boiler

daver123

Hi,

Does anyone know the correct temperature setting for a baxi condensing boiler ( the boiler is a megaflo 24 he ie ).

Thanks

The correct temperture is whatever temperture you need to keep yourself warm, I like to set a stat on the boiler to 65c, lower than 60c and you have to take legionnaires disease in to account, over 70 and rads can start to get hot.

You have to take preferred temperture, type of heating system and system controls in to account, everybody is different.

For a condensing boiler you want the return temprture to be below 56c to get the boiler to continually condense.

daver123

Thanks gary71, if i want to get a return of 56 should i set the boiler temperature to 65 - 70

daver123

daver123 wrote: »

Thanks gary71, if i want to get a return of 56 should i set the boiler temperature to 65 - 70

It's your control knob so you need to put it at a temperture that suits you taking the above in to account, the return temperture would be dependant on system design and desired room temp, the lower the flow the more Likly the boiler will condense.

shane0007

daver123 wrote: »

Thanks gary71, if i want to get a return of 56 should i set the boiler temperature to 65 - 70

To keep the boiler in full condensing mode you will generally require a delta T temperature difference of 20C. The ideal flow temperature is 73C with a return of 53C.

To enable this, the system needs to balanced, possibly increase the size of radiators, a modulating circulating pump and a balancing valve between the flow and return.

shane0007

shane0007 wrote: »

To enable this, the system needs to balanced, possibly increase the size of radiators, a modulating circulating pump and a balancing valve between the flow and return.

Your absolutely right, but I have yet to see this or DT of 20.

Do you think when replacing a boiler it's worth upgrading in the manor you mention to get the extra 4-5% lost due to the reduced time a boiler condenses on "normal" rads?

shane0007

It really depends on the system parameters really. The problem is you can achieve the 20C delta T when all circuits are open quite easily but when say hot water circuit only is on then this is much more difficult.

I have had lengthy chats with Stephen Grant about the possibility of incorporating a small buffer tank onto the side of an oil boiler and make it a system boiler with a modulating Grundfos Alpha pump to keep the boiler in condensing mode. Economics wins every time!

shane0007

shane0007 wrote: »

The problem is you can achieve the 20C delta T when all circuits are open quite easily but when say hot water circuit only is on then this is much more difficult.

Yep, with a system that has a fluctuating demand, achieving DT across the board would be difficult, I havn't seen many who have cracked it at my end of the market and I wonder for the savings over a exsisting installation out their how practical it would be.

shane0007

A Grundfos Alpha pump is a huge help. Basically open all circuits, set the full power button and it will modulate down from there as required when circuits/TRV's close down.

A thermostatic balancing valve between the flow and return will also be a decent aid.

shane0007

shane0007 wrote: »

A Grundfos Alpha pump is a huge help. Basically open all circuits, set the full power button and it will modulate down from there as required when circuits/TRV's close down.

A thermostatic balancing valve between the flow and return will also be a decent aid.

Don't forget now I'm just a gasman so I have to work with whats in the boiler, but I'd be interested to know how you think a T balancing valve would work in a usual gas installation.

shane0007

Basically a thermostatic link between the flow and return. It will only ensure the return will not fall below the required/desired return temperature. I suppose more advantageous with a non-condensing boiler that is under-sized for the installation.

It comes more into play with varying demand types such as UFH and radiators within the same installation.

shane0007

Forgot to mention the thermostatic balancing valve is called an ICV (injection control valve).

Also if you look at radiator manufacturer sizing charts, you will have 2 different sizing charts. One at 62C and the other at 52C. The 62c is for standard efficiency boilers with the 11C and the 52C is for high efficiency boilers.