Adding CH to new loft - advice please

[abuse]

Hi all,

I've just had a new loft conversion done (well, it took about 12 months what with the loft company taking forever to finish and the decorators mucking around and eventually running off - fortunately with me owing them money rather than the other way around).

Due to some bad advice and planning early on, there is no central heating in the conversion (which is a bedroom with balcony ie lots of Velux, plus a bathroom). The bathroom is all tiled, with electric underfloor heating and an electric towel rail. The underfloor is nice as it keeps the tiles from freezing the skin off the soles of your feet in winter, but the towel rail is awful - takes ages to warm up and uses masses of electricity without really heating the bathroom. Also the bedroom is very cold - the old insulation in the original ceiling seems to be stopping any heat from the rest of the house from making its way upstairs.

Ideally I'd like to extend the central heating upstairs, so I'd appreciate any comments from those in the know. First here's a summary of the CH/HW system:

Boiler is an old Potterton Netaheat 10-16 Mk II F, conventional gas-fired boiler, pumped, with a 3-port motorised valve. There is a cold water tank in the eaves space, a hot water cylinder in the airing closet on the 1st floor next to the pump/3-port valve, and the header tank for the CH is in the apex of the roof not next to the cold water tank. The CH is a micro-bore system (with feed and return at opposite ends of the radiators). I have no idea where the manifolds are located.

Based on the airing closet and loft location, the following scheme is possible in terms of running pipes - I'd like to know if it's feasible though:

- tap into the CH feed just after the 3-port valve

- take the pipe straight up about 2m to the ceiling of the 1st floor then under the loft floor into the south eaves (about 3m), across the outside of the loft room wall (another 3m) then enter the loft room

- install a long low radiator or two into the loft room along the 5m wall, with return to the eaves space

- across the eaves again (8m) and into the bathroom, with a single radiator

- back into the eaves (5m) under the floor (3m) and down to the original junction (2m) for a total of about 30m extra pipework

- presumably a pressure relief valve would also be needed between the new outbound and return pipes

Does this sound feasible? Effectively it creates a combination of single pipe loop and micro-bore piping, but other than locating and hooking into the split of the hot feed into the manifolds & the corresponding return is there anything else I can do? As the loft will get the freshest hot water, will the returning water still be warm enough to heat the rest of the rads (there are 12 existing radiators at the moment)? The eaves spaces are uninsulated (well the floor and walls of the eaves are but the roof is just the back of the tiles) - would the CH piping need to be insulated to retain the heat or is that overkill?

Alternatively I could install a new 2-port valve on the Ch side of the

3-port valve, to split the CH system into two separate circuits - one for the existing house and another just for the loft. This way the loft circuit would just have the loft radiators on it, and a separate thermostat could be used so that the two zones are independently regulated. This would require a more complicated control system than the current mechanical/thermostatic one though.

Does the pipework have to be copper, or can parts be plastic? Owing to the spaces that need to be worked in, parts might be really difficult to work in copper.

Is the existing pump likely to need to be replaced to handle the work of pumping hot water up 2.3m above what it does currently? Or is it ok since the header tank is right at the top of the house ie way above the proposed new loft radiators?

I haven't done any formal calculations on the boiler rating to see if it has sufficient output to heat the new space but gut feel says its ok as it can heat the original parts of the house pretty fast from cold; also the new loft is well insulated so should retain its heat well if I can just get it in there in the first place!

I've read about using long low radiators which resemble standard skirting boards but are metal and contain two pipes for feed and return, which I could run along 5-10m of the room instead of using conventional radiators. Any thoughts?

Thanks, Zane.

[Andy Hall]

It's a bad idea to try to combine a one pipe and a two pipe system and to be honest a one pipe system is not great to begin with.

Really, you should plan to add the new pieces in two pipe. This doesn't need to be done in microbore or into a manfold. You need to tap into the main (probably 22mm) run after the 3 port valve as you say but then find the return.

Since the pipe runs are quite long, it is important to size the pipes adequately - don't guess because you will be disappointed if you make them too small.

There is a note on how to do this at

need to size the radiators to meet the heat loss and then the flow rate required and pipe size are determined from this. Again, do do the proper heat loss calculations using one of the radiator company's programs - don't guess or you may have another disappointment like the towel rail.

The number of radiators is irrelevant. What matters is their heat output. You can get these figures by measuring them and referring to manufacturer data sheets. On a conventional boiler such as you have, the actual outputs will be 89% of the numbers in the table because the temperature is lower than that used for testing them.

Ideally the pipes should be run on the inside of the insulation. However, if you have to run them outside the insulation, then they must be insulated with pipe insulation of at least the pipe diameter thick - i.e. the total insulated size of a 22mm pipe becomes 66mm.

You could do that, but it might need more work on the rest of the system to convert it to use entirely two port valves. If you look on Honeywell's web site it is called an S-plan plus system then. You could just zone it off with a two port valve, but then the loft heating is at the mercy of the rest of the house if you see what I mean.

yes.

It can be in plastic if you like.

Hard to say. The issue is delivering the volume of water at the rate required - both will increase as a result of this addition.

As long as you have about a metre of head of the tank above the top radiator circulation should be OK. The issue is as above.

Don't work on gut feel. This is not a large boiler so again you may be disappointed. On the other hand, it is probably due for replacement and you could simply try it out and replace the boiler if it proves to be inadequate.

Myson make them among others. I've used them in a similar situation to yours. I've also used long conventional radiators 300mm high.

You have to see whether you get enough heat output for your requirements.

.andy

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[Peter Taylor]

snip

The old insulation should have been removed. This would make the loft bedroom much warmer, probably enough to need only very minimal heating, if any. Is it impossible to remove it now? This seems like a lot less work than all the heating extensions you are planning.

Peter

[abuse]

It would be tricky as it is no longer possible to lift the floorboards. However with a bit of stiff wire and some patience it may be possible to fish it out from the eaves.

However this would increase the heat loss of the 1st floor bedrooms, as the heat would be able to escape into the loft. Once the insulation is out it will be very difficult to impossible to put back. You can sort of see how it's been done here:

like the idea of improving the heating without installing CH but I'd hate to make the 1st floor cold as a side-effect. Any ideas as to whether this would be a problem?

Thanks, Zane.

[abuse]

Thanks for the quick & detailed reply.

Fair enough. However if the CH is split in two (as described below) surely a single pipe system of just two radiators is not such a bad thing? It's not long enough to end up with the last radiator being too cool.

How would I go about finding the return? There is no access to any of the pipework except in the airing closet where the hot comes in. Presumably where the coil exits the hot water cylinder is a return - would that join the CH return and would it therefore do to connect the loft radiator return to the hot water return?

Would it work to tap into the main with a simple T (and same again at the return)? Ie would enough water flow up 2.5m in this situation, or would it require a motorised valve to shut off the "easy" route of the existing CH piping?

probably do it.

Agreed.

What about a second 3-port valve installed on the CH side of the existing

3-port valve? This could split the CH water into two circuits. If controlled by a thermostat in the loft, then this could switch the CH hot water between the circuits, favouring the loft first. This could then be independent of the rest of the system. The loft would heat before the downstairs but once warm enough the downstairs would heat up. As long as the loft thermostat had a range (eg heat to 20 degrees, but don't reactivate until temp drops to 16 degrees) there wouldn't be excessive switching between the two.

I'm hoping not to have to do this for a while, but might be forced into it.

Thanks, Zane.

[Bob Mannix]

Even if there were no insulation there in the first place, the requirements for 30 minute fire protection between the old house and the new loft conversion would require new mineral fibre insulation beneath the floor of the loft conversion, nailed to the joists. To remove it would be highly irresponsible. The new room requires its own heating. To extend the CH will almost certainly require repositioning the header tank. The common approach is to fit an electric wall heater with integral timer and thermostat. The loft room should be well insulated and will heat up quickly.

[Peter Taylor]

Bob Mannix wrote

You are right about the ceiling needing to be 30 minute FR, but this is achieved by the plasterboard and skim (or by lath & plaster in older property). Thermal insulation material laid above the ceiling adds nothing to the ceiling's fire resistance. As I said, the original insulation to the area of the new loft floor should have been removed - this is not needed as there will be new insulation on/between the rafters. The original insulation in the eaves should remain unless the new rafter insulation is carried on down the slope to joist level.

Peter

[Christian McArdle]

Yes. Perfect for it, provided it is run in 22mm.

Making the water flow down all the lines when the zone valves are all open is called balancing. You will need to balance the entire system after it is all plumbed in.

Why do you want to favour the loft? A properly balanced system will get all the radiators in the house hot fast. To subzone, I'd recommend replacing the

3 port valve with multiple 2 port valves.

If you must keep the 3 port valve (i.e. it is a diverter and you like HWC priority), subzone just the heating circuit with an extra two 2 port valves. Wiring then gets slightly more complicated as it is non-standard.

Christian.

[Christian McArdle]

I disagree. If the OP intends to have subzoned heating, then insulation between zones is actually quite useful, as heat required for occupied rooms doesn't leak into unoccupied zones.

Christian.

[Bob Mannix]

I don't believe you are correct. A single sheet of skimmed plasterboard is insufficient to provide the fire protection (unless it is Fireline plasterboard). The requirement for mineral fibre insulation was part of the fire protection requirements for my loft conversion and its protection was added to that provided by the ceiling to make up the required 30 minutes. A depth of 65mm of mineral fibre insulation, nailed to the joists either side was required (glass fibre is not allowed as it melts). The floor was not allowed to be laid until the BCO had inspected the installation of the mineral fibre.

Two sheets of plasterboard with a 12mm (AFAICR) gap would also do, but that's a lot more difficult.

[abuse]

Interesting. The plans state various FR requirements including the floor-boards, insulation, doors etc. They were approved and the BCO made several visits including before the floor-boards went down. The insulation between the 1st floor ceiling and the 2nd floor boards in the original

50mm insulation that went in years ago - no special mineral fibre.

To where? It's already in the apex of the roof, ie in the ceiling of the

2nd floor. As it's there already I am thinking of piping in new CH as I believe in the long run ...

... it will be cheaper than electrics (especially if I can do it myself for the cost of the materials + my time and a few crates of beers for my more handy friend with all the tools). The loft bedroom is large (5m x 3m

• 1.5m x 2m = 18m2) and so is the bathroom (5m x 1.8m).

One thing I was considering instead of CH is to install an air conditioner with integral heat pump. Apparently the heat exchangers are very efficient, and as the loft gets very hot in summer air-con will be a nice-to-have anyway.

Zane.

[Andy Hall]

The problem is that you are going to feed the entire house heating circuit around this extra loop, and I suspect that you would have real problems getting balancing to work between the different parts.

The exit from the cylinder coil will eventually join the return going back to the boiler. However, it is not a good idea to connect your additional radiators to that point. You should really connect to the return from the heating immediately before where the cylinder coil return joins it. There's a fairly good chance that it will be close to the cylinder and probably under the airing cupboard floor. If you are going to use zone valves then connecting to the return near the cylinder should be OK.

This is why you need to do the pipe resistance calculations. You need to make sure that the new pipework has enough water carrying capacity to cover the needs of the new radiators.

The flow between radiators on the new part and those on the old part need to be balanced. This will mean that you will have to balance radiators on the old part of the system against the new. It may also be necessary to increase the pump setting. In principle, there is no reason why a pump can't cover a three floor building - it really depends on the flow conditions in the system.

It's actually not that bad. At a guess, I suspect that you will end up wanting to use 22mm for most of the distance to the radiators and

15mm for immediate connections, but it does depend on the heat requirements. You might be able to get away with 15mm throughout.

You could do that, but it might cause some funny temperature effects around the house. If you use an electronic type of thermostat you could play around with setback temperatures and with hysteresis (i.e. the difference between the on and off temperatures).

You can check that pretty easily by measuring and sizing the existing radiators.

.andy

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[River Tramp]

The current requirement is for sound insulation to a loft conversion floor means mineral wool is required, and as the floor needs to be 30min FR, the wool will often need to be laid on chicken wire drapped over the joists. The boarding & wool has to be taken eaves to eaves (ie the void areas also need it).

RT

requirements

[Tony Bryer]

If you do you might just have problems with radiators getting warm when they shouldn't: if returns from the heating connect into the system at two different points (A and B in the diagram below), when the DHW is on the pressure at these points will be different so you may get a reverse flow through the radiators.

reverse circulation ------+------->------+----------< CH flow (off)- || --+ RAD RAD | reverse^circulation V | | | Pump | +---A------->------B------------------Boiler --X----MV | | CYL | | | +--------------------------------

[Bob Mannix]

requirements

Well I can only quote my own experience. "Mineral fibre" just means Rockwool or similar, as long as it's not glass fibre - nothing special. It may be that the plasterboard and floor boards together just about make it to 30 minutes and some authorities allow you to get away with that and some insist on the extra given by the mineral fibre to give a safety margin. If it is indeed old insulation and is not nailed to the joists and is even glass fibre, then pulling it out will not be irresponsible, as it's doing nothing (in terms of fire protection).

Sorry I may have missed the current tank position in an earlier thread.

Yes - for an area that size, you are probably right.

Noisy though, and it's cheaper to open the windows!

[Andy Hall]

[Peter Taylor]

Bob Mannix wrote

I don't know any details about your loft conversion Bob, so I pass no judgement on whether you are right or wrong. I can say for certain that I have never come across a BCO requiring thermal insulation when upgrading the fire resistance of ceilings. Maybe there was an issue about sound insulation in your case?

I checked my copy of the British Gypsum White Book just to make sure my understanding was correct. There are various different constructions considered but the two important cases are:

a minimum 15mm thick T & G flooring on 38mm timber joists at 450mm centres with a ceiling of 9.5mm plasterboard with 5mm skim coat gives ½ hour (modified) FR. The Building Regs permit this relaxed construction over rooms but not over the escape route.

b ditto but with 12.5mm plasterboard and 5mm skim gives full ½ hour FR. This is what the Regs require over escape routes.

There is no requirement for thermal insulation in these details I am looking at.

I've also never heard of using 2 sheets of plasterboard with a 12mm gap. In the above examples, 2 staggered layers of 12.5mm wallboard (without skim) will give

1 hour FR and 2 layers of 15mm Fireline unskimmed will give 1½ hours FR.

You can see the latest on-line version of the White Book on timber floors and ceilings on

at page 4 onwards

Peter

[abuse]

What about just installing one-way valves on both the cylinder return and new CH return just before the two returns join? That will prevent the HW return from supplying hot water into the new rads, won't it? Actually the one-way valve on the cylinder side would not be necessary as it wouldn't matter if hot water returning from the radiators made its way into the cylinder coil, would it?

Zane.

[Andy Hall]

It may work.

You don't want water flowing through the cylinder coil either when not wanted, because it may transfer heat out of the cylinder.

There are three basic kinds of non return valve, as far as I am aware.

- The first is typically used in a mains water supply to prevent back flow of water and is normally based on a spring loaded plunger. I am not sure that you can get these suitable for the low pressures in a heating circuit.

- The second type is intended for vertical mounting with an upward water flow and has a small weight or flap inside. These are typically used in the pumped heating part of a system when a back boiler is in use with gravity hot water.

- The third type is based on a metal disc which swings. These can be mounted horizontally or again vertically on an upward flow.

Look at

part 7463 and 7464

.andy

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[Bob Mannix]

< snip stuff where I am sure you are correct but which differs from my experience! I am in Vale of the White Horse District Council (Oxfordshire) >

As it happens my brother (same county but different district & planning area) is in the middle of a loft conversion by a national loft conversion company - I was there yesterday and could see the construction of part of the stair wall which had the first layer of plasterboard and then battens to take the second layer - he told me the rest of the walls were the same.

As an aside, having used Fireline plasterboard myself with no problems (aside from its weight), I can't understand why anyone would use two layers of ordinary instead, irrespective of the regs!

Thanks for the reference.