DIYblonde is in BIG trouble!!!!! Can you help?

[diyblonde]

Hi there - I'm in trouble!

My head is spinning around (like Kylie) I'm being thrown so much info I'm getting a bit overwhelmed.

We are doing the central heating from scratch. This is a 3 bed 2 bath detached house with 2 stories (which may later get another bed and bathroom addition) which right now needs 70 000 BTU for the rads. What boiler do I get?

The plumbing is in a complete mess ( I didn't see the horse outside when the plumber arrived and I've been told by 3 central heating engineers that it's rubbish and has to be re-done - luverly.) Now that I've been educated - a little - I'm horrified at what has been put in. So most - if not all of the pipework needs to be re-done anyway regardless of what boiler is chosen.

Two central heating engineers have suggested an unvented system 30W and not less than 100 000 BTU. The other one has suggested a floor standing Worcester combi. The combi does up to 99 thousand BTU, but I've been told by the other two that it won't cope with the load ... which is why I should have an unvented system.

But if the combi does 99000 BTU why won't it cope??? Or will it???

Arghh!

Am. Very. Confused.

Any advice would be a lifeline ... I don't know which way to go on this. Unvented system or worcester floorstanding combi?
Thanks .... diyblonde

ps Please don't tell me "I told you so" on the plumber ... I just didn't see it coming. He's a lovely guy - but his plumbing is not.

 

[Nixt]

Hi there - I'm in trouble!

My head is spinning around (like Kylie) I'm being thrown so much info I'm getting a bit overwhelmed.

Sorry in case I'm wrong but this approach is usually employed by someone who far from Kylie looks more like a cross between Mrs Slocombe and Boris Yeltsin. Either that or a sad bloke.

 

[gas4you]

Forget the combi on a 2 bath system. Go for a system boiler and unvented cylinder.

I to would go for a 30Kw, the Vaillant Ecotec Plus 630, and range rate it down to 22Kw for now.

Also go for a unistor 210S and a VR65 control unit.

This all assumes you have a good cold mains pressure and flow rate.

 

[ChrisR]

try dying you hair mousey grey?

 

[D_Hailsham]

We are doing the central heating from scratch. This is a 3 bed 2 bath detached house with 2 stories (which may later get another bed and bathroom addition) which right now needs 70 000 BTU for the rads.

1. Are you putting in a complete new system, including radiators or just a new boiler?

2. If new rads, were they sized using calculations of the heat loss in each room, or was it just a guestimate?

3.Where did you get the figure of 70000BTU from? Was this based on the calcs in (2) or another guestimate?

If you want a good estimate of the size of boiler you will need, go to Sedbuk and run the "recommended boiler size" utility. If you are going to extend the house later, you can include this in the calculation to make sure that you have a boiler big enough for the future.

If you are going to have so many bathrooms then a Combi Boiler would not be suitable.

 

[diyblonde]

Thanks Dave and D_Hailsham for your advice so far to answer your questions;

1. Are you putting in a complete new system, including radiators or just a new boiler?
2. If new rads, were they sized using calculations of the heat loss in each room, or was it just a guestimate?
3.Where did you get the figure of 70000BTU from? Was this based on the calcs in (2) or another guestimate?

A new system including rads is going in.
New rads were calculated by online BTU chart http://www.tertullian.org/rpearse/heating/radiators.htm.
The 70 000 BTU figure was a calculation from all the rads needed on the calculations, it actually came to 68 000 but I rounded it off.

I'm going to double check a couple of calculations on other sites to make sure they are accurate ....

I to would go for a 30Kw, the Vaillant Ecotec Plus 630, and range rate it down to 22Kw for now

Dave - I hear you on the unvented but I am torn because we are so tight on budet EVERYTHING has run over.

I guess one reason the 30KW Combi Worcester looks attractive is because it is a cheaper option. I spoke to a builder friend who actually has the combi in his house ... it services him, his wife and their two kids in their 4bed 2bath. His advice was do the unvented if money is no concern but the combi will cope. Do you agree?

many thanks

ps Nixt no offense taken but definitely way more Kylie and no sign of Mrs Slocombe!

 

[tabs]

I've installed the worcester you're talking about and it is excellent. As long as you are not planning to run 2 baths at once you should be ok with it. The last house I did had 2 bathrooms as well as utility ,it just depends what sort of use you want out of it. You could always put an electric shower in one of the bathrooms to relive some of the demand to the boiler

You should however make sure you run 22mm pipe as far as possible from the boiler to the draw offs.

 

[DIWHYCHICK]

thanks Tabs good to know

 

[diyblonde]

Thanks Tabs .. will consider the electric shower ...

 

[D_Hailsham]

A new system including rads is going in.
New rads were calculated by online BTU chart http://www.tertullian.org/rpearse/heating/radiators.htm.[/QUOTE]


The calculator you used is very old and does not take account of current regulations. The fact that it uses BTU is a dead giveaway, also the fact that it is dated 1998.

Although it does not give a room by room analysis, the Sedbuk calculator I mentioned earlier will give you a total figure for the size of boiler you need for Heating. It also includes a figure for Hot Water (2kW).

NB BTU=kW x 3414

If the sedbuk calculator comes out at approx 20kW, then the rads you have should be OK

You say that you are installing a completely new system. This means that it has to meet the current building regulations, though presumably your installer is aware of this and will be making sure it complies and will deal with all the legal requirements.

As for the combi/non-combi argument, The boiler will need to be well over 20kW to provide a decent flow of hot water, particularly if you have more than one tap/shower/bath running at the same time. Remember that, when the HW is being heated up, the CH plays second fiddle.

 

[diyblonde]

Thanks D_H I will go to the calculator you suggested and check it out. We've had some central heating guys around and the general thought is that 30KW will do the job. Is there a more up to date site that does the rad sizes for individual rooms or is that one OK for that purpose?

 

[Bon]

If you're tight on budget then why not look at a system boiler and traditional vented indirect cylinder?

The only way a combi would be suitable in a house that size is if it's well over-sized, which gets rid of the efficiency arguement and also increases the strain on your budget.

As for putting an electric shower on a combi to relieve the load, then surely that tells you on all but small houses, combis are pants.

 

[Andy165]

Rough guide to sizing radiators = width (of room) x length x height x 5 will give approx. btus to heat the room and put a trv on it. E.G. 13ft x 12.6ft x 8ft x 5 = 6552 btus. Pick rad. to suit and you can,t go far wrong.

 

[diyblonde]

Hi Bon ... do you have any specific boilers in mind?

Thanks Andy I'll check my calcs against that. Any things to think about re outside walls and other factors that will influence?

 

[D_Hailsham]

Thanks D_H I will go to the calculator you suggested and check it out. We've had some central heating guys around and the general thought is that 30KW will do the job. Is there a more up to date site that does the rad sizes for individual rooms or is that one OK for that purpose?

There are more detailed calculators such as the Quinn Radiators (formerly Barlo Rads) which you will find here:

http://www.quinn-radiators.co.uk/downloads_heatloss.php

You will need to download and install it on your computer. It will then enable you to carry out a detailed calculation of the heat loss in each room, taking into account the construction, window types, required temps etc etc. It comes with a PDF Manual which is fairly good.This will enable you to get accurate figures for radiator sizes.

The disadvantage of the Room Volume x 5 approach is that it tends to over estimate the rad size and does not take construction into account. It was prevalent in the 1960's when central heating was just getting popular and it was safer to over-specify.

The advantage of the Sedbuk "whole house" method is that it assumes any heat lost between rooms can be ignored (most people don't keep the doors shut all the time!); it's only the heat lost to the outside which has to be accounted for.

I have used both Sedbuk and Quinn calculators and they come up with very similar results. They can also tell you what the effect of, say, putting extra loft insulation or cavity wall insulation would have on the rads and boiler.

There are more complicated calculators, such as the one used to work out the SAP rating of a building, but you almost need a degree in thermodynamics to understand it

As you are putting in a completely new system, which will include a condensing boiler, your calculations can make sure that the boiler works at its most efficient for the maximum time. This means that the return temperature to the boiler should be about 60°C

I hope I am not getting too technical for you, but it's is worth getting it right when you are doing a complete makeover.