boiler and rad sizing

[its cold here]

Hi newbie on here so forgive my dumb questions.

I've a glowworm ultimate 100ff which i believe is 100,000btu's output, what is the maximum amount of btu's i can have on the radiators when I add them all together. My house is always cold and I'm trying to determine if i can upgrade the radiators by changing the rads.
Most of the rads are 30years old and all are Myson but without any convector fins on them. Was wanting to change for the newer Mysons with fins for better heat output but didnt want to overload the boiler.

Thanks

 

[AWheating]

what size/type of hot water cylinder do you have?

 

[its cold here]

Err not really sure its a copper one with a jacket round it and no markings that i can see. Takes up about half the airing cupboard and looks like its been here forever. Sorry I know thats not what you asked but short of putting a tape measure round it i dont know.

 

[Gray0689]

What size of a house is it??

 

[its cold here]

its an extended 4 bed with 3 showers and 2 baths

 

[AWheating]

at a guess i would think that your cylinder would account for 10,000 to 20,000 btu's which leaves the rest for your heating system.

 

[its cold here]

Hi thanks for that if my rad calcs are correct I'm using about 50,000 btu leaving plenty of scope for upgrades and a chance to be warm lol.

One more question is, I've read that fitting a boiler bigger than needed is a waste of gas/money. As we have now established that this is what I've got at present will i see any increase in gas bills once i use all my remaining 30,000 btu's (or some thing like that)?

 

[AWheating]

your boiler can most likely be range rated/adjusted via burner pressure to suit the system requirements. (not sure on this exact boiler) tho most get left of full setting. but yes the more energy you use the higher your bills

have you got trv's? roomstats? time controls?

fitting trv's will help reduce your energy consumption.

 

[its cold here]

Some of the new rads in the extension have trv but most are fitted without them. The older ones have both feed and return pipes going into the same point on the radiator so they cant be fitted untill i change the pipe work around to suit the new rads, but i will be fitting them at this time.

Apart from that just one room stat.

 

[WHPES]

Slightly oversized boiler won't make a lot of difference. True, if its bigger it needs more energy to get hot, but your losses elsewhere will be greater. Look at TRVs etc. It doesn't matter if your radiator is oversize as you can control the amount of heat with balancing and TRVs. After all, the more surface for heat transfer, the more efficient it is.

 

[its cold here]

Thanks to all for taking the time to spread some knowledge its greatly appreciated

 

[kirkgas]

fitting TRV's to properly sized rads will reduce energy bills by reducing consumption of fuel, but as you are too cold we need to go back to basics and work out whether your boiler can take bigger rads which i'm sure it will, then you need to calculate the exact requirement of each room, google rad design or heat loss etc you will find plenty of help, divide your 100000btu by 3412 to give kw's which will assist you on calculations, usually allow 2/3kw for your hot water so leaving plenty of scope to renew rads, but as i say back to basics first by checking rad fitted, temp of flow and return to ensure water is as hot as it should be, no point in doubling size of rad on a system with a dodgy pump or dirty water which is causing poor circulation, might be worth investing in the technical help of someone on site to service set up and check the boiler first then look at the wet side of the system

 

[its cold here]

I've been doing the calcs for each room but im struggling to find rad info for the myson rads with out the convector fins. I've found a calculator somewhere that gave me a formula to work it out and according to that most of the older rads are under sized. I agree that the boiler needs checking and setting up correctly but as i said above a lot of the rads are fitted with single entry points into them, so these need changing first i think and its a job i can carryout (hopefully!!). I plan to swap 4 of them over to new ones and size them according to the room requirements calculators on line. Now i know the boiler is big enough i think ill go this way first then once done ensure the boiler is working and set up correctly.

 

[WHPES]

For the old Mysons without the fins, assume 3/4 of the output of those with fins. The fins effectively double the surface area of the rear of the radiator (well not quite but its not a bad approximation)