I have a problem with finding out more about boilers and what size I need for the house.
Ordinarily I know the correct thing to do is to get a registered Corgi plumber in to quote for the whole of the central heating system and to supply and fit a boiler within that price. This is what I have done and whilst I can get another more competitive quote the first proposal was too high.
Subsequently I approached a friend of ours who is currently on a plumbing course if he would like to do the work at the house (apart from the bit connecting to the gas supply of course). He is up for this as it is difficult to practice when you are training and getting a house to do from top to bottom is excellent experience. Whilst he is comfortable with every aspect of laying the pipes etc he is not sure about how to calculate what size boiler is required and nor am I.
I have scoured the web for sites that help to calculate it but have not been very successful. After a lot of messing around I think I need a 24Kw Combination Condensing Boiler for a house with 6 radiators, one shower, one bath and three sinks. It will be well insulated with double glazing (the house that is not the boiler!).
I have no idea if this is appropriate and will need to continue my research.
Obviously our friend will be checking with his tutors on his course but I prefer to try and understand these things rather than just taking people’s word for it. It would be an expensive error if we bought the wrong one.
Ordinarily I know the correct thing to do is to get a registered Corgi plumber in to quote for the whole of the central heating system and to supply and fit a boiler within that price. This is what I have done and whilst I can get another more competitive quote the first proposal was too high.
Subsequently I approached a friend of ours who is currently on a plumbing course if he would like to do the work at the house (apart from the bit connecting to the gas supply of course). He is up for this as it is difficult to practice when you are training and getting a house to do from top to bottom is excellent experience. Whilst he is comfortable with every aspect of laying the pipes etc he is not sure about how to calculate what size boiler is required and nor am I.
I have scoured the web for sites that help to calculate it but have not been very successful. After a lot of messing around I think I need a 24Kw Combination Condensing Boiler for a house with 6 radiators, one shower, one bath and three sinks. It will be well insulated with double glazing (the house that is not the boiler!).
I have no idea if this is appropriate and will need to continue my research.
Obviously our friend will be checking with his tutors on his course but I prefer to try and understand these things rather than just taking people’s word for it. It would be an expensive error if we bought the wrong one.
6 comments:
For boiler sizing, any boiler manufacturer’s technical department may well be helpful.
Personally I would stay clear of a combi boiler – good idea in principle but they do struggle when demand is high. Having had one years ago if you have room I would suggest separate units.
R D Treloar "Plumbing" has a section on boiler sizing. I can lend it to you if you like - it is a good book.
The dishwasher will use v. little hot water. The only issue is the bath. The key is to minimise the distance between boiler and shower/bath, as you lose a lot of heat with every inch of piping. At very least you must insulate the DHW pipe all the way from the boiler to the tap, inc any bits hidden in the wall. Otherwise you are throwing away heat.
We have a combi boiler. It is a Worcester Bosch 24CDi. I am sure you can google the kWh rating. If you want to measure the hot water flow rate, you can do so at the party this weekend. That will give you an idea of the power, and whether it is strong enough. My gut feeling is that 30 is too much - I think that is more than ours.
Also, I think the temperature is a temperature rise, not level.
Which? magazine test boilers, again, I can try to dig you out the recent test
Ah, the bit about the temperature rise would make sense. I did think that 35 degrees seemed a bit low. That does mean that the boiler can produce hotter water in the Summer and lower in the Winter. Makes sense I suppose but that isn't the way round you would want it really!
You are also spot on about the insulation. I think the official measurement is something like "a tap 1 metre from the boiler" which is not far at all. Luckily in this house the distances from boiler to bath and shower will be quite small so we should be fine.
The Worcester Bosch 24CDi is discontinued now but if it is like all of the other boliers I have looked at the 24 bit gives the Kw rating. Your house is a lot bigger than this one so that would indicate that 24Kw would be ok.
Yes, my assumption is that our boiler is 24KWH. The water is the same temperature at all times, what happens is that the flow rate changes seasonally. Given that it is cold now, measuring the flow rate at the weekend will be a good way to see whether it is fast enough. Our house is 1800 sq ft, but don't forget that it is well-insulated - cavity wall insulation, modern dbl glazing, 8" loft insulation.
Where are you going to put the boiler? I would look into putting the boiler at the house end of the kitchen, rather than the other end. That will shorten the run to the shower by the length of the kitchen.
Also, check the SEDBUK ratings - they are online. The 24KWH is input, not output, I think, so you need to multiply it by the SEDBUK % to work out how much heat it will deliver.
Without wishing to appear to mercenary, I would point out that, curiously, very few people look at anything in great detail when buying a house. So purely from the point of view of maximising profit I wouldn’t worry about the manufacturer, but perhaps it’s worth paying for a name that you (and thus others will probably) recognise. By the same token, going for a good brand name for the kitchen appliances would also give the house credibility as they are one of the few things in the house that are obviously badged. As your plumber is inexperienced it might be worth him checking with his tutor as to which manufacturer’s boilers are the easier ones to fit, if the tutor has recent knowledge which he may well not.
As you might gather from the above my instinct would be to go for the 24Kw model, but if you such a party animal that you want to check flow rates remember that the current water temperature is still relatively high as the ground is still warm from the ‘summer’.
PS. When Jona Lewie sang, “You'll Always Find me in the Kitchen at Parties” I never though he checking combi boiler flow rates!
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