change radiators with new combi boiler?

[finest1]

hi all

following from my other post about combi boiler recommedations, i've had a few installers visit me over the last few days.

there was one in particular that stood out from the rest. yes he came to see the Combi install but at the same time was talking to me about efficiency in heating the home. he did not like the look of our existing radiators! he advised that changing all the radiators will be more efficient as the new style radiators are made to be heat efficient compared the to the radiators of old. (the exsiting radiators have been with us since 1987!!) they are the big double ones. ovbiously it was advisory, but he stood out as the only one that was looking at the whole house, as well as doing the install. so i thought i'd throw it out to the forum and see what you guys think. do you think radiators need to be changed too?

thanks, and happy new year!!

Finest1

[dewaltdisney]

Changing them is a good idea as the latest radiators can be up to 50% more efficient than the current radiators installed. This is more important these days and coupled with a good flush, valves, and a simple Thermo control system it should be a good investment for your dad. I think the installer who specified that would give me confidence as he is clearly thinking it through thoroughly rather than being the cheapest to get the job.

DWD

[Rorschach]

How are they more efficient DWD? In terms of speed of heating a room? I can't see how they could be more cost/fuel efficient.

[dewaltdisney]

They are lower capacity heat up quicker therefore using less energy.

DWD

[Someone-Else]

If I could have afforded it when we had our boiler changed I would have done it, not only are new rads more efficient, where do you suppose sludge comes from?
We had a rad changed recently as you could see the rust on it, rads rust from the inside out.

[stevei]

We had a new combi fitted when we bought our current home 11 years ago. The fitter changed all the radiators and swapped as much of the microbore pipe for 15mm pipe as he could. Made a huge difference to the speed of warming up the house.

[Rorschach]

They are lower capacity heat up quicker therefore using less energy.

DWD

They use less energy to heat up, but that doesn't make them use less energy overall.

[dewaltdisney]

This is not really relevant in ice Station Zebra R.

Less water to heat and keep to temperature

DWD

[Razor]

A radiator can't take less heat to warm up - the specific heat capacity of water is (basically) a fixed parameter.

However if you are changing from old rads that are just two panels without the metal wriggles in between it's a very different situation.

The old style rads worked by radiating heat, (obviously) so you get a hot spot at one end of the room.

The wriggles between the panels change the heat profile. You still get the radiated heat but cold air will be drawn into the space between the panels and as it goes up the wriggles it picks up heat and you get a convection effect where the heat travels across the ceiling then falls towards the floor. This means the rad effectively covers a far greater area.

It's a pretty good idea to have the rads changed but you need to ask the installer to perform a heatloss calculation for each room to make sure they will work at the new Building regs Part L requirements which all heating engineers are supposed to be fitting too but probably less than one in fifty does.

This will ensure the rads can be run at 55 degrees and still heat the house properly and will make a massive difference to you gas consumption

[wine~o]

Probably worth considerig Cost vs. Return regards the radiators, may or may not be worthwhile. I'd ask your guy that quoted for the boiler how much in terms of % not pounds sterling you could expect to save old vs. new radiators and whether he will do a heat loss calculation as Razor suggests.

[Rorschach]

A radiator can't take less heat to warm up - the specific heat capacity of water is (basically) a fixed parameter.

However if you are changing from old rads that are just two panels without the metal wriggles in between it's a very different situation.

The old style rads worked by radiating heat, (obviously) so you get a hot spot at one end of the room.

The wriggles between the panels change the heat profile. You still get the radiated heat but cold air will be drawn into the space between the panels and as it goes up the wriggles it picks up heat and you get a convection effect where the heat travels across the ceiling then falls towards the floor. This means the rad effectively covers a far greater area.

It's a pretty good idea to have the rads changed but you need to ask the installer to perform a heatloss calculation for each room to make sure they will work at the new Building regs Part L requirements which all heating engineers are supposed to be fitting too but probably less than one in fifty does.

This will ensure the rads can be run at 55 degrees and still heat the house properly and will make a massive difference to you gas consumption

A bigger rad takes more energy to get it hot, but the overall energy consumption is the same as a smaller rad in terms of heating the house. So my original point was correct. You can only increase efficiency in terms of how quickly you can warm the house, you can't get any more efficient in terms of energy usage which is what the plumber was suggesting (or seemed to me anyway).

[dewaltdisney]

You are missing the point about the reduced capacity of the water in the system. As there is not as much water to heat it is more efficient similarly the room heat build up is quicker with the convection of the newer style radiators tripping the thermostat to close the boiler until needed.

DWD

[Razor]

A bigger rad takes more energy to get it hot, but the overall energy consumption is the same as a smaller rad in terms of heating the house. So my original point was correct. You can only increase efficiency in terms of how quickly you can warm the house, you can't get any more efficient in terms of energy usage which is what the plumber was suggesting (or seemed to me anyway).

Sorry you are still wrong.

Oversizing the rads allows you to run at a lower flow temp and get the same output. The figures suggest that almost 90% of condensing boilers in the UK don't actually condense because they aren't set up properly and too high a flow temperature is the most common issue.

To understand the situation properly you would need to know how the output is calculated for a standard rad, (ie what mean water temp and delta it's based on) and you would also need to know how to work out the output of the rad at a lower flow temp.

If the boiler is not running in condensing mode you will drop the efficiency down to around 85%. Almost 10% more gas consumption then is needed.

So yes new radiators can put the boiler in condensing mode and lead to decent longterm savings as long as everything is sized appropriately

[Rorschach]

Ah now well that's a separate issue. The way the original point was made, and the response from DWD was that the newer rads use less fuel. That may or may not be true but isn't down to the rads themselves, but having the correct setup on the system. Old rads on a properly set up system are just fine and won't be improved by replacement. New rads on a badly setup system won't be anymore efficient just because they are new.

When our boiler was installed the engineer tested all the temps and set the boiler at a temp at which he said would be the most efficient in terms of condensing. No rads were changed even though they are more than 40 years old because he said the system looked perfectly fine. He could have got a lot more work for himself as most of the replacement cost would have been covered by a grant.