Rad sizing

[mutley racers]

When sizing rads using the method ft3 times 5=BTU's does this include the extra 20% for condensing?

Also, i am quoting for a whole house install and am thinking of putting in a system boiler. Does anyone have any makes they like? I am looking at viesmann or Vailiant. Probably vailiant 618.

So all floorboards up and down stairs. rip all old out and replace with new system. Boiler, 10 rads and hot water cylinder. How long should this take on my own do you think?

And any rough ideas of pricing? I like the add 20% to final bill method as I always seem to come up short in the end from something i missed

 

[petercj]

I've got a Valliant ecomax pro which has developed problems due to restriction in the small bore pipe used in production of the heat exchanger - having sought opinions on here about boilers with larger bore heat exchangers, the Viessmann and the Atag came well recommended on this site, you might want to check out opinions on this thread:-

http://www.ukplumbersforums.co.uk/central-heating-forum/37878-boiler.html

In every other way the Valliant has run without fault, but I wouldn't buy another one with such a small bore heat exchanger fitted.

 

[fuzzy]

When sizing rads using the method ft3 times 5=BTU's does this include the extra 20% for condensing?

Also, i am quoting for a whole house install and am thinking of putting in a system boiler. Does anyone have any makes they like? I am looking at viesmann or Vailiant. Probably vailiant 618.

So all floorboards up and down stairs. rip all old out and replace with new system. Boiler, 10 rads and hot water cylinder. How long should this take on my own do you think?

And any rough ideas of pricing? I like the add 20% to final bill method as I always seem to come up short in the end from something i missed

extra 20% for condensing? rads are designed with low flow temps so if sized correctly as per rad schedule and condensing boiler is set up properly then the boiler will condense. i find its just clouding the issue to consider it at this stage, it shouldnt come into it

 

[chris watkins]

R U having a laugh mutley is this what you call heatloss calculation to size rad's ??? This (ft3 x 5 = BTU's x 20%) is no better than guessing !! you might as well stick to the does it fit under the window. Why don't you get your self a heatloss program & do a professorial job Myson, Heatline or Stelrad all do them on either CD or to down load for FREE & it does not take to long to master them. (& you don't have to use there rad's either).

 

[mutley racers]

oh is that right fuzzy? these days we don't need to add 20% then for the boiler to condense?

Chris, i have looked on here for ways to calculate as a rule of thumb and that method has come up a couple of times

 

[fuzzy]

the boiler must have a return of around 55 degrees to condense. If the flow is set at around 68 then with properly sized rads it should return at a temp which will ensure it condenses. in reality who sets up the flow so low? most people whack it up anyway and it barely condenses

 

[petercj]

On the sizing issue, have a look at Valliant's range before scratching your head too much - the choice in the eco max pro range fives years, or so, ago was 18.5kw, or 28kw. According to pencil and paper calculations, the 18.5 was too small, and the 28 was too big for my property.

Because of the condensing issues I opted for the 18.5. The undersizing has hardly ever been a problem, i.e. if everything was on at once the boiler wouldn't keep up, but with TRVs it's not a problem in practice. But if you are sizing for a customer, I guess oversizing is a safer bet for you than undersizing - although maybe Valliant have more choices in their latest range.

If they've got kids, allow a couple of extra KW's - they never shut doors!

 

[SimonG]

Nowt wrong with cubic feet x multiplier (dependant on room) to give an estimate of rad size.

 

[petercj]

Allow 1kw per child on top.

 

[mutley racers]

wow so many different ideas and methods people use. Thanks for the input guys. So simon, would you or have you ever used the cubic ft way? I also remember being on the honeywell course and they said you should add 20% extra for the rads. But only calculate boiler size for the original calculation without the 20%. It is all a bit confusing.

 

[chris watkins]

Nowt wrong with cubic feet x multiplier (dependant on room) to give an estimate of rad size.

Because as a professorial you would not surely want to estimate the size of something as important as a heat emitter.
Ever noticed the difference in size between a rad in a new house & one in an older one yet they are the same size rooms ??

 

[SimonG]

Because as a professorial you would not surely want to estimate the size of something as important as a heat emitter.
Ever noticed the difference in size between a rad in a new house & one in an older one yet they are the same size rooms ??

Must be unprofessional then.

I know what works and what doesn't and I'd rather use the cubic foot method and take two minutes to find the rad size than take longer to get exactly the same result.

 

[Best]

That cubic feet x method seems surprisingly accurate, as I have been working out a room heat loss by online calcs + a Mears calc & that give the same as the highest results I got, - although I would add 10 or 20 % usually, especially for larger rooms or colder regions & also considering condensing boilers.

 

[fuzzy]

Nowt wrong with cubic feet x multiplier (dependant on room) to give an estimate of rad size.

in most cases yes, all too often poor plumbers will guess the size and add 50% because they are afraid of undersizing. the upshot is rads waaaayy too big and more water to heat, they rely on the trv too much. if we are honest a properly sized system wouldnt need trvs

in my opinion it depends on the size, a small house this system is fine, anything bigger then i would be more accurate

 

[Roger Welton]

Other than cost, oversizing in my opinion is not such a massive problem, it allows for lower flow temps and giving the same amount of heat into the room.

 

[mutley racers]

awesome. thanks guys. i shall use this method for now but i have just downloaded the stelrad stars app so shall use that for any thing bigger

 

[tamz]

Btw you should be able to do the job comfortably in a week (5 days)

 

[mutley racers]

a week?!!! wow, that is ripping up boards and taking out all old pipework? I was thinking more like 2 weeks

 

[mutley racers]

it takes me 2-3 days to do a combi swop with powerflush, wiring and commissioning. I must be really slow. Am glad my clients still don't mind paying me!! he he

 

[tamz]

a week?!!! wow, that is ripping up boards and taking out all old pipework? I was thinking more like 2 weeks

It would take me 2 days on my own, 2 1/2 if i paced myself but i don't price things on a day rate:smile:

A week should do it easily. Just think ahead of what you are doing and it all falls into place.

 

[fuzzy]

Other than cost, oversizing in my opinion is not such a massive problem, it allows for lower flow temps and giving the same amount of heat into the room.

whilst heating up much more water in the process. how does a bigger rad allow for lower running temps???? you control the temp at the boiler

 

[mutley racers]

right tamz. as this is my first big quote on my own i asked the guy who taught me how much to quote roughly. he said 4k for just labour. if it did take me a week, i think the client would be wondering about the quote. Although, they are getting in someone else to quote as well.

But the thing is, the builder who is running the project is more likely to come to me as he uses me all the time

 

[mutley racers]

and the electrician who is doing a whole re-wire said 3 weeks and 3,1/2k for labour. and the builder has got labourers in to chase all walls and so on. So i don't want to be much cheaper than him as its just the same amount of work i thinks?????

 

[mutley racers]

sorry for diverting the thread to an off topic thread chaps

 

[petercj]

New EU regulations come into force next year re sizing. They take into account the behaviour of inhabitants and calorie burn.

The assessment involves a questionnaire that is mandatory and must record certain information in relation to all occupants, such as: how much time they spend watching TV, and use of the remote; how many times a-week they have sex; how much time they spend arguing; whether the kids are HDD, etc.

Apparently, research shows that randy parents with six rowdy kids who fight over the remote require 50% less heat input per square metre than a couple who live the quiet life.

Assessors will need to register, and be able to show that they have level one C&G 6372 in counselling, and Relate 217 in mediation skills.

The Government are calling it the: 'Small Clean & Green Radiator Assessor's Program', or SCRAP for short.

Watch this space for more details.