Background: We live in a 3 bedroom house-on-a-hill. From the front it looks like a bungalow. Once inside you go downstairs to the bedrooms. The (non combi) boiler is in the garage on the front. The hot water tank is downstairs in the airing cupboard (pumping hot water downstairs against convection, hmm who thought of that one!). There is a header tank in the loft. The CH radiators are all on Microbore pipe. In the 6 months we have lived there the CH top up tank has required about 2-4 litres of water to top it up. We had a combi boiler fitted in our last house (non condensing
"ChrisJ" wrote | I've also been told that if your system leaks a combi boiler | will make it worse because of the pressure. (Remember its needed | toping up already!)
If by 'combi boiler' you actually mean sealed pressurised radiator (primary) loop, then the *advantage* of this is that if there is a leak, the amount of water in the system is limited. With a header tank (fed by mains from a ballcock) the amount of water is unlimited.
| ATM my understanding is our DHW comes from the hot water tank in the | airing cupboard downstairs (there's also a pressure vessel in there | too, not sure what for though).
But from where does the cold water come from for the hot. From the "header tank" or is the hot water tank (cylinder) actually a mains pressure hot water system?
| Does the above sound feasible? (IE are there any glaringly obvious | mistakes I've made or things I've overlooked.?)
It sounds like you don't want a combi, so you don't need a new boiler. You need a pressurised primary system and a mains pressure hot water system.
| Are there issues with microbore pipes for CH? | Can you mix micro bore and standard piping in one CH system?
No and yes.
| We will then have the possibility of using 2 showers at the same time | (one a floor up from the boiler and one a floor down from the boiler if | than makes any difference). I'm presuming some sort of HW storage tank | (as opposed to a combi) will be required to allow both to be used | together. Is this the case (most "Combi yes/no?" threads so far have | only concerned one shower being used. Could a combi and mini tank be | used or would the best idea be to go for a mains pressure storage tank | solution?
Mains pressure, I think. Remember you do have the option of having some taps/shower on the 'hot water' part of the combi, and a conventional hot water cylinder powered by the 'radiator' part of the combi.
| As the back half of our garage has been converted to a store room there | is not a space issue with putting a hot water tank in there with the | boiler but I'd prefer it to be compact as possible.
As you will be taking a 2 storey to a 3 storey building you may be subject to additional fire precautions with your loft conversion. I say "may" because with a middle-floor ground level you may be able to plead exemption.
You can avoid the hot water taking ages to reach the taps by taking a loop back from the far end taps to the cylinder and putting in a circulation pump. With insulated pipes and the pump on a timer for peak use periods only, there should not be significant energy loss.
Thermostatic blending valves below all the hot taps except the kitchen may save accidents.
With 3 storeys you might want to put some cabling in for a home intercom system.
I'm struggling a bit to understand your current setup! You mention a header tank in the attic. I assume that this is a large tank (50 gallons or so) acting as the header tank for the hot water supply?
You also mention a top-up tank for the heating. Is this the *same* tank, or are there two? If separate, how big is it, and where is it? You also mention a pressure vessel. I am confused about this, because if the primary circuit (i.e. the "sealed" circuit taking water from the boiler to the indirect coil in the hot water cylinder and to the radiators) is non-vented (pressurised), there won't be a top-up tank - but there will be a filling loop and pressure gauge instead.
As I see it, you need, in addition to your existing requirements:
Extra radiators in the attic at a height equal to or greater than your existing primary circuit header tank (if any!). This means in my view that the primary circuit will *have* to be pressurised.
Hot water delivered to the attic for the new shower/washbasin. Whilst your existing hot water flow is gravity driven from the header tank in the attic, your new shower/washbasin cannot be gravity fed without raising this header tank above roof level!
You thus need a mains pressure hot water system for your upstairs requirements. There are three and a half possible ways of achieving this:
Replace the existing conventional boiler with a combi, and use it for all your hot water requirements. This is a BAD solution - particularly if you want to use both showers at the same time, or have lots of baths.
2A. Install a mains pressure hot water system, still heated by a (new or existing) conventional boiler. This is fine as long as you've got adequate mains pressure/flow - but needs expert installation because you'll have a
*lot* of hot water at high pressure.
2B. Install a heat-bank, heated by a conventional boiler - and obtain instant mains-pressure hot water via a plate heat exchanger. Almost as good, and can be DIY'd.
Install a combi boiler, but retain your existing stored hot water system. Let the HW side of the combi provide just *part* of your hot water requirements - I would suggest the kitchen sink and the new upstairs shower. "Zone" the CH side of the combi so that it heats both the radiators *and* the hot water cylinder. Use the hot water from the cylinder for the downstairs bathroom/shower. You will still need a header tank for the hot water, of course. You'll have lashings of hot water for baths, and no problems running 2 showers at once because one will be using the stored hot water and the other will use instant mains pressure hot water from the combi.
I think 3 would be my preferred solution - but you'll still have to find somewhere for the header tank. [Actually, you could go for a combination of
2B and 3 - getting the combi to heat the heat bank. You wouldn't then need a header tank.]
I haven't attempted to answer the questions about micro-bore and pipe runs - lets get the basic principles established first!
Old wive's tale. With respect to the heating system, a combi boiler is not really any different to a system boiler. Microbore pipe is a form of pipe - there is nothing magic about it either positively or negatively. What you do have to do, and should do with any system design is to make sure that the bore of pipe used is adequate to support the water flow rate required for each radiator. If you look at the web site of the Copper Development Association, there is a downloadable paper on how to calculate this. Where 15mm pipe is used, it is possible to get away with some degree of murder in that a reasonable length will support flow for about 6kW of radiators. Similar lengths of microbore will support 1-2.5kW which is normally one radiator. It is why microbore systems are often done with manifolds but there is nothing to mandate that. If an installing firm is giving you stories about microbore, it either means that they don't know how to calculate for it or can't be bothered. Either is a flag to consider shopping elsewhere.
Not exactly. it's more a function of the primary radiator circuit being sealed and pressurised. Mainly combis are used on sealed systems, but this is a separate issue.
If the system has old radiator valves, it is worth changing them for good new ones like Pegler, anyway. Then with competent plumbing, you won't have leaks.
In any case if you do, the situation is better than with open vented systems because the volume of water is limited.
No it isn't, but there is no reason not to use microbore. If the space needs a lot of heat (i.e. > 2.5kW or so) then it mivht imply two radiators, but that's probably a good idea for heat distribution anyway.
If you add radiators using 15mm and the rest of the system is microbore, then in order to balance it, you will need to turn down the lockshield valve on the new radiator(s) so that the flow becomes comparable to microbore anyway - somewhat defeats the object.
If the radiators are in good condition, there is absolutely no need to replace them or the pipework. If the plumber is leading you on this path, you are being taken for a ride.
It certainly does make sense to give the system a good clean by either emptying and taking the radiators outside for a good flush, or by using a powerflush machine. Don't get suckered into paying multiple hundreds for this service - you can rent the machine and DIY it quite cheaply.
Is there a large and a small tank in the loft? If just a small one, then it means that your HW system is pressurised. Unless you go for a very large combi with production rate of at least
15litres per minute, you are going to get inferior results to it. In that scenario, with young kids, I would try to keep the cylinder. You could go for a combi to supply the kitchen requirements perhaps and keep the cylinder to rapidly fill the bath and give good showers.
Otherwise, if you have a large tank, then the implication is that the primary circuit is sealed already.
This is reasonable as long as you make sure you insulate the pipes in the garage.
Yes, although I would check into what you have as a cylinder. If it's pressurised and you have the space, I would keep it.
None apart from those mentioned.
Yes, although bear in mind the balancing issue.
I would check the radiators. Don't replace them for the sake of it. If the system has had inhibitor in it, then they should be fine.
If pipework is changed, it would add a lot to the cost and is not really necessary. There is no reason to change it to 15mm, even if the radiators have had it. I would just take one off and have a look. and see if there is much sludge. Careful because it stains.
Discounted Heating.
If you have a high end combi at 22 litres per minute, it would imply
11 litres per shower at shower temperature in the winter. I think that that is marginal.
Some form of storage of the hot water, or a heatbank would be a much better choice if you think that you are going to use two showers simultaneously and decently.
You could look at a CPSU. This is a floor standing unit with some water storage inside. Whether that is enough to last for the duration of a shower where women are involved is another thing.
If you are using microbore it is soft and you can thread it through holes in the joists. With 15mm, you would have to line up the holes perfectly and joint together short sections - not a good idea.
You can thread plastic through joist holes as well.
15mm copper is normally put in by notching the joists. If you can avoid that then it's a Good Thing.
No. It might mean that the installer has little experience of fitting anything except combis and/or does not have any microbore fittings in the van.
See my Sealed CH FAQ. below.
Yes; but it's only a matter of balancing the flow between the new and old radatiors.
Since the existing heating is open and the HW cylinder is vented I can't think what it does. What is it connected to?!
A hybrid system with a combi heating nearby small DHW and the airing cupboard tank, might well serve you best.
If there is no HW needed in the loft conversion then simply pressurizing the existing primary (if the existing boiler is good for this) is a simple option.
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