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

 

[Nostrum]

No offence taken, and as a professional plumber and heating engineer I will continue to use the method that is proven and works for myself.

You could also get yourselves a 4.8 v8 Chevy ( proven, tried and tested method that works) to carry your tools around in, but you wouldn't !.....? :hand:

 

[SimonG]

and you could cut the crap

 

[petercj]

Big room = Big radiator ... Medium room = Medium radiator ... Small room = small radiator

Big house = big boiler ... Small house = small boiler (ref: Vaillant eco pro max range)

Over-sizing unlikely to lead to come backs, whereas under-sizing might.

Job done!:yes:

 

[Nostrum]

and you could cut the crap

Sure thing pipe monkey



Seriously though sometimes you have to accept that things change, nothing about what you were doing before being wrong, just a different way otherwise we would still be burning coal.

 

[SimonG]

I refer you to post #62

 

[SimonG]

Anyway what's supposed to have changed?

All the old stone buildings with no insulation?

 

[Nostrum]

Double glazing, loft insulation, fitted carpets, less ventilation but more importantly an accurate method for figuring heat loss using a logical process rather than a formula written on the back of a *** packet in 1950.

Bottom line is each to their own, I don't care how big a radiator you specify as it won't be going in my house.

I'm surprised that some of the things people are advised against on here could be seen as trivial (whether or not to put jointing compound or PTFE on an olive) yet sizing a radiator and ultimately a full heating system in the correct way is frowned upon.

 

[SimonG]

I'm not frowning upon anything and if I had to sit down and design a heating system for scratch for money then calculations it would be. All I'm saying is that I can go and do a quck calculation (in my head) and define the rad or rads there and then. All based on experience and what I see.

I used to think this was magical because my boss used to do this when I was an apprentice. He would have me calculating the U value of all the surfaces using r values and define the heat loss down to the nearest btu. My calcs and his estimate would be within 50btu's either way.

All I'm saying is that it works for me and rarely get it wrong.

But to be called unprofessional because that's the way I do it is not on.

 

[Nostrum]

With all due respect simonG I did specifically say that no offence was intended. I'm not doubting or questioning your experience or ability in the trade, I've no right too, I don't know you and I've no interest to do so either. (doubt you)

The example above about being 50 btu's out cannot possibly be correct seeing as a simple change in wall construction from solid to insulated cavity could cause a greater difference and the ft2x5 rule of thumb can't allow for construction material.

Its pretty obvious not just from your replies but from the general response that the method me and Chris Watkins are familiar with isn't common practice amongst the majority on here and most definitely not with the majority of engineers I have met or worked with over the years in my area. That's not surprising as most systems aren't installed with economy in mind. If it gets hot enough it works tends to be the general approach, and it will because the rule of thumb and mears calculator All oversize by quite a way.

Its almost like saying we should put a 35mm gas supply in for every new boiler because it will always work.

All I will say is that times are changing and new technologies and restraints call for more accurate methods in sizing emitters, heat pumps being a prime example. If required there are spreadsheets available for free that make the whole process take about 2 mins per room, a little more if the construction material is non standard.

I'm happy to agree to disagree, and if you genuinely thought my comments were out of order, I apologise as it was intended to be a bit tongue in cheek and certainly not meant to cause offence.

 

[SimonG]

We agree to disagree then.

 

[chris watkins]

All I'm saying is that it works for me and rarely get it wrong.

But to be called unprofessional because that's the way I do it is not on.

How do you know that you don't get it wrong then Simon ? if you don't do a calc involving measuring the room & windows, checking the construction of the building etc how would you know? You, & I agree most other plumbers do guess-emate to size a rad & that includes no corrections to the rad table outputs which are based on a temp difference of 50deg C.
Do you know what I believe Sambotc, I think the hostile reaction we receive ever time this gets brought up (not just on this forum) has more to do with the fact that a lot of plumbers & so call heating engineers do not know how to do this, have no interest in finding out how it is done (even when it is reasonable easy & won't cost them either), they just keep on telling anybody who will listen that they have the 'power' to predict what the heat loss & rad size will be, based upon years of experience dating back to when BTU's where used & their plumber handed on this sacred knowledge. Even though as you say time s have moved on, designs, boilers, heat emitters, insulation etc etc have all moved on !!!!!!!!

 

[Nostrum]

It will filter through I think in the next few years as the courses start to include it. As i said above ive no interest if people don't want to know about the changes. In fact I see it as a bonus if I have to quote against a company who pulls numbers out of a hat or if I can sit down and work out the specific requirement on site in minutes and explain the process to the client.

 

[chris watkins]

one of the same Sam, one of the same.

 

[Mike Jackson]

When I quote a job I always specify the room temperatures that I've allowed but not the rad sizes. I tell the customer that they can have a copy of the calculations including the rad sizes when the job is accepted. If I'm in a rush when doing the quote I can guesstimate the rad sizes needed and do the proper calcs if i get the job. I normally find my guesstimate is larger than the required size.

 

[stevetheplumber]

ive always been a 5 per sqft man and also own a mears wheel for larger than the normal 3 bed house
its all very well having the wonderfull program for calcs if you are on new build work where a u value of each surface is probably an email to the desinger away
how do you work out the u value of a retro fit into a single flat in a block of flats built by persons unknown which is clad in some sort of finish you cant id ?where you dont know if the flat above and below may be heated or not and theres no access to loft space to check insulation levels ?

 

[chris watkins]

ive always been a 5 per sqft man and also own a mears wheel for larger than the normal 3 bed house Would that be a stone built with single glazing or a new build or something in between ?
its all very well having the wonderfull program for calcs if you are on new build work where a u value of each surface is probably an email to the desinger away
how do you work out the u value of a retro fit into a single flat in a block of flats built by persons unknown which is clad in some sort of finish you cant id ?where you dont know if the flat above and below may be heated or not and theres no access to loft space to check insulation levels ?

Simples, you do your best with would you can see but of the other 90% of the time you don't guess.

 

[chris watkins]

When I quote a job I always specify the room temperatures that I've allowed but not the rad sizes. I tell the customer that they can have a copy of the calculations including the rad sizes when the job is accepted. If I'm in a rush when doing the quote I can guesstimate the rad sizes needed and do the proper calcs if i get the job. I normally find my guesstimate is larger than the required size.

Now that's standard tender / quoting practice, Mike & I totally agree. No point in wasting time working it all out if no job at the end & why give info away as to what you are going to fit (mainly cos it will be a lot smaller that the others) but when it comes to selecting one well then sizing is a must.

 

[SimonG]

I thought we'd put this to bed and stopped all the petty mud slinging? Chris.

 

[chris watkins]

I thought we'd put this to bed and stopped all the petty mud slinging? Chris.

You hadn't posted for a while, didn't know that you had decided the tread should be shut down! Who's slinging mud ? Not me.
PS. If anybody whats any help or advice in doing heatloss or rad sizing correctly, just post in the arms or mail me.

 

[SimonG]

Busy working, fitting oversized radiators with trv's.

 

[chris watkins]

Busy working, fitting oversized radiators with trv's.

Well clearly you are not busy but if you must have the last word on this thread, so be it.

 

[SimonG]

Lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol 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[SimonJohns]

I can't see the point in my mears guage. It's quite good at stopping the table from wobbeling.

If a rad looks good in a room and you know it can heat the room. Then that's what their having

From what I can see this has been a pointless discussion.

From what I can see the ill experienced of us use calculations to avoid mistakes. And the experienced ones use their head.

 

[kay-jay]

Lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol lol 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Lol

Sent from my GT-I9100 using Tapatalk 2

 

[Nostrum]

I can't be arsed to argue/discuss any further, i'm not a mud slinger, mud wrestling with a fitty, maybe.

but please, before we say cheerio to this obviously useless thread, please answer me one question sensibly and logically.

Why would you spend time sizing a gas supply based on the required demand, but not a radiator on the same principle? We are talking about over sizing rads, so why not oversize a gas supply?

My guess is that its because installing an oversized gas pipe is hassle, hanging an oversized rad on someone's wall, nowt.

That's it from me

 

[PlumbersMate]

Chris Watkins would you mind inboxing me more details on how to work out correct size needed please? No rush but I'm intrigued after all this if not a little overwhelmed and would love to understand it all a bit better. Thanks

 

[SimonG]

Well that's made somebody's century

 

[Masood]

If anybody whats any help or advice in doing heatloss or rad sizing correctly, just post in the arms or mail me.

PM'ed you. It's an area that I don't know much about and I'd like to understand it better. Energy efficiency is here to stay, might as well learn all the ins and outs.

 

[petercj]

Surely there must be a computer program for this?

Whipping out your lappie in front of the customer when doing a quote and using a laser measuring gismo, and maybe an i.f. thermometer too, should impress over a few notes on the back of a *** packet?

 

[chris watkins]

Chris Watkins would you mind inboxing me more details on how to work out correct size needed please? No rush but I'm intrigued after all this if not a little overwhelmed and would love to understand it all a bit better. Thanks

PM'ed you. It's an area that I don't know much about and I'd like to understand it better. Energy efficiency is here to stay, might as well learn all the ins and outs.

Hi all, that are interested the book I recommended does not seem to be available from Amazon. Had a quick look around & if you are not a member of CIPHE then cheapest is through this link £23.99.
http://www.centralheating.co.uk/Dome...g-Design-Guide
I think it is the "bullhooks" not just for heat loss.
Peter, I use Myson Rads or Heatline CD (one of the same thing) which are free apply on-line, there is Stelrad's one called STARS which you can download & I am sure lots more, but to use them effectively you need to understand the basics which is where the books come in.
The level 3 JTL book has a section in the system planning at the back, which is not to bad.
Hope this helps