Radiator sizes

[G4RHL]

Does anyone in the forum know of a site that is known to give accurate estimates of radiator sizes? I have looked at a couple, put in my data and end up getting different answers, one site does not even take account of insulation and other factors. My house was built in 1997 and I am sure the builder simply put in what he thought was right based on raw room sizes. I have a couple of rooms that I know could do with more powerful and efficient radiators but it is not a major issue at present. However, I am now into my 19th year of use and know my boiler will need replacing before long and it seems sensible to replace one or two radiators with ones that are more efficient. Finding out the correct size is not as easy as I thought.

[paulockenden]

I don't know how accurate it is, but this one seems to ask all the right questions: http://www.homesupply.co.uk/radiator...calculator.php

[emmeesse68]

You are right, it's not easy.

When I built my heating systemI spent an afternoon at an engineer computing heat dispersion based on wall type and thickness, neighbouring rooms, size and type of Windows and doors, orientation of walls and roof, type and thickness of floors, ...and so forth. This work gave me the basics to compute radiator sizes, the dispersion for each room, that means the power (in watt) that each room would need to keep the temperature steady.

Then you'll need to find radiators capable of a power that's greater than that, if you want to be able to heat up your rooms. The greater the power, the faster your rooms will be heating up.

With a control system like a EvoHome I'd choose large radiators rather than stingy ones, to be able to keep up with colder days and to make the system capable of heating up quick enough. With such an assumption, having an accurate radiator computation is quite useless, just stay on the large side and your EvoHome will take care of the rest.

Large radiators will also mean your boiler could keep lower water temperatures, resulting in better comfort and efficiency, if you choose a condensing boiler...

[G4RHL]

I don't know how accurate it is, but this one seems to ask all the right questions: http://www.homesupply.co.uk/radiator...calculator.php

Thanks, much appreciated.

[G4RHL]

You are right, it's not easy.

When I built my heating systemI spent an afternoon at an engineer computing heat dispersion based on wall type and thickness, neighbouring rooms, size and type of Windows and doors, orientation of walls and roof, type and thickness of floors, ...and so forth. This work gave me the basics to compute radiator sizes, the dispersion for each room, that means the power (in watt) that each room would need to keep the temperature steady.

Then you'll need to find radiators capable of a power that's greater than that, if you want to be able to heat up your rooms. The greater the power, the faster your rooms will be heating up.

With a control system like a EvoHome I'd choose large radiators rather than stingy ones, to be able to keep up with colder days and to make the system capable of heating up quick enough. With such an assumption, having an accurate radiator computation is quite useless, just stay on the large side and your EvoHome will take care of the rest.

Large radiators will also mean your boiler could keep lower water temperatures, resulting in better comfort and efficiency, if you choose a condensing boiler...

Thanks for the advice. It is the Evohome system that has drawn my attention to the fact some radiators ought to be bigger. Basically get a good idea of the size and then go bigger.

[no8080]

Builders always fit rads that are too small for a room, they often take in to account people and appliances in the room as heat sources.

Which is fine for occupied rooms, also bigger homes, say 4, 5 or 6 bedrooms builders will assume a high occupancy of the home, which is not always the case.

I have a modern build 6 bed home, but there is only me, wife and my daughter. All the rads are seriously under spec'ed. It's fine when we have visitors, say 4 adults in the living room, then it's warm, otherwise I have to have the heating on all day to keep the room at a decent temp, it takes about 3 hours to heat the room otherwise.

OK, so my advice, based on my experience. Find out what ever rad manufacture you have now, if you post a picture of one I may be able to identify it. If you have a single panel rad then fit a double panel double convector of the same size, width and height, this is the simplest DIY method, no messing with pipes etc. You need to slightly pull the valves to meet up to the new rads filler holes, if you have plastic plumbing then great, if not check there is a bit of slack in the pipes.

If the room is very cold, even with the rad on full, then replace the single panel rad with a double convector, same width, but go for the tallest (highest) rad you can get. If you can not go taller, then move up two sizes in width, you will need to relocate one or both of the wall brackets and redo the plumbing though.

You sort of get a feel for spec'ing rads, the calculator are no good, as factors such as number of external walls, window size, glazing type, bay windows affect the calc, an experienced heating plumber will use his experience, and likely use the calcs and add 20% to the estimate they provide.

Neil

[G4RHL]

Builders always fit rads that are too small for a room, they often take in to account people and appliances in the room as heat sources.

Thanks. In my case my wife grumbles the lounge is cold, never is when I go in (to me that is) but it does warm up more with two people in the room. I'll work out the sizes and take a view on what to upgrade but wait until the boiler needs replacing.

[no8080]

Fitting bigger rads does not mean you have to fit a bigger boiler, the opinion on this was to add up the BTU requirement of the rads and add 10K BTU for the boiler, that gives the size of boiler you need. Of course, you may be replacing the boiler for different reasons here, I am making an assumption.

Doesn't work in most cases, if that was the case I would need a 250K BTU boiler in my house. It works fine on a 80K BTU, and that's after I have sorted the rad sizes out. I have swapped out 75% of my rads.

Trick here is, builders nearly always fit the same size rads to house, cheaper to buy the same size in bulk, regardless of the room requirements. So for bigger rooms, fit two or more rads, thats what builders do. That's also why most modern homes have the same size windows throughout as well.

I come from a family of house builders, so my experience is first hand, not criticism of them.

The benefit to use though is, you can likely use some of the rads you remove from some rooms to upgrade other rooms. You need to think about the rads in your house, replace the coldest rooms with new rads of same design, use the ones you remove in other rooms, even if the room is OK.

For example, my hallway rad was a double convector, same size as a bedroom rad, so I removed the hallway one and replace the single convector rad in the bedroom with the hallway one.

Bigger rads mean the room heats up quicker, yes it places more demand on the boiler, so it will stay on longer and not go through cycling until the house is warm. Won't cause an issue as long as the boiler has a bypass valve and pump overrun fitted.

Neil