Converting to Zoned Central Heating

I'm converting my loft to create a couple of extra rooms and about to start thinking about plumbing in some central heating.

I currently have a combi boiler whose outlet/inlet splits for ground floor and first floor, but isn't zoned. I am planning to splitt three ways at the boiler to take the hot water up to the loft, then splitting again to do the two rooms.

I'd like to end up the four zones as it makes sense to add zone valves while I'm cutting the existing pipes and the new loft needs to be two zones as there's a small room which will be used as an office during the day, so it'll be neat to be able to leave the house cold and have a toasty work space.

I've not done much of this before, so wanted to run my plan by some experts and check I'm doing it right and not missing anything.....

So my plan is 4 zone valves on the returns, two at the boiler for the ground floor and first floor, then two in the loft on the returns to the split in the loft. Does that sound right? And do I need to retain a bypass circuit? If so, how is that normally done?

Any recommendations for zone valves? I would need two for 22mm pipe and two for 15mm pipe.

1. You need a room thermostat for each of the four zones, unless you use "intelligent" thermostatic radiator valves.
2. You do need a bypass. There may be one already inside your boiler (check manual). If not it needs to be as close to the first branch point as possible to allow maximum pipework to cool the water when it operates.
3. My personal preference is Honeywell V4043's. I don't think they do a 15 mm valve, so you'd need 22 mm to 15 mm fitting reducing couplers such as Screwfix 61183.

Dont put the zone valves on the returns, the will be noisey when closing, put them on the flows

I'm happy putting the valves on either, a quick Google said put them on the returns so they are kept at a lower temperature. Is that not better than a bit of noise when they close, or is the operating temperature not a problem?

I'll check the bypass, from memory the boiler doesn't have one. What's the purpose of the bypass exactly? It would be better if one of the valves was programmed to sit open when the boiler is off, to give a larger circuit for heat dissipation, but I suppose it's a fail-safe incase that valve fails closed.

I have a single room thermostat at the moment, it's one of the Tados, I know I need another three and I think I know how they all work together, that's one for some more googling and maybe another thread. I think I just need to run control wires to both the valves and to the boiler for the new ones to cover all options and then sort that out later. I think my existing extension kit will control the boiler and the individual thermostats will control their valves, but if anyone knows better please shout up!

The bypass is there to allow the boiler to dissipate heat when none of the zones require it. Imagine the whole heating system running, then one by one the zones are satisfied, closing off their zone valves. The pump will still be running against a closed load, and need to be bypassed so that the water can circulate until the boiler stops the pump.

OK, so is the bypass for the pump or for the heat or for both? And is the bypass valved as well, or what stops the water just circulating the bypass and not bothering with the radiators?

These days the bypass is automatic. It is essentially a spring loaded valve connected between flow and return. Once water pressure exceeds the spring pressure, the valve opens, allowing water to flow from flow to return. The bypass does not normally have valves fitted.

You would also need to connect the thermostats, probably through a relay or series of relays, to ensure that when all thermostats are satisfied, the boiler is turned off. Its called interlock, and is a requirement of the building regulations. You could probably obviate this with a four channel programmer / timer.

The Tado system manages the boiler demand for the for controllers, with a box wired to the boiler. The four thermostats then control their zone valve and all the boiler box to turn the boiler on. I think. So that side is relatively simple, so long as I put wires in from the wall boxes to the valve locations.

Bypass sounds simple enough too, though it would be neat if it could just be programmed to open one of the zone valves.

There are a few different ways to control zones, as already said the boiler modulates its output depending on return water temperature so there needs to be return water at all times, so the by-pass valve ensures water can return to the boiler.

I am told EPH do a thermostat range where one is the master and the others are slaves which can work with OpenTherm so you can have zones with modern condenseing boiler, I don't know of any others, however the normal way to form zones is to use thermostatic radiator valves (TRV) rather than zone valves and thermostats as it reduces the wiring required, and likely does a better job.

However systems like Wiser, EvoHome, Tado, and Hive get rather expensive when the TRV heads cost around £50 each, you can get cheap programmable TRV heads for as little as £10 if you don't want wifi and linking to the main thermostat, so the big thing is to decide what if any cost cutting measures can be taken, and this depends on your home, in the last three houses I have lived in, upstairs is never cold, heat raises, and the main thing is to stop higher floors getting too hot, so ground floor may need TRV heads linked to a main thermostat, but upper floors can use stand alone programmable TRV heads.

oldbuffer said:

1. You need a room thermostat for each of the four zones, unless you use "intelligent" thermostatic radiator valves.
2. You do need a bypass. There may be one already inside your boiler (check manual). If not it needs to be as close to the first branch point as possible to allow maximum pipework to cool the water when it operates.

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I hear this word "intelligent" and "smart" and it seems all programmable TRV heads do have features which could be called "intelligent" and "smart" but it really depends which features you want, and what you want to pay, including a yearly fee for using some systems, even the really cheap eQ-3 stand alone programmable TRV has a open window detection so I use one in the kitchen so it auto switches off heating for ½ hour when outside door is open as I unload shopping from the car. Now with geofencing the rooms are only heated when your phone is detected within a selected distance from home, I know my Energenie TRV heads can be set up to turn up heat as I travel home, using IFTTT, however they also have a anti-hysteresis software which means to hit target temperature can take 2 hours, the Wiser TRV heads have a memory built in so they can reheat the room without over shooting far faster, each system is slightly different and it is a jungle trying to work out which system is best for any house.

And that assumes they do what they say on the packet, the Energenie I bought were claimed to link to Nest, and in a way they do, but not in a successful way, I ended up removing the link and simply setting same schedule, EvoHome and Wiser have a good name, rest are suck it and see, there have been reports of Hive TRV heads not being strong enough and loosing wireless links, but one has not idea of other factors, insulating foil on plaster board can stop wireless links, so one has no idea if the bad report down to house design or Hive design. All I can say is how mine work, I find batteries last around 2 years, but to be certain they are going to work I change batteries every year, so with 9 electronic TRV heads that's 18 good quality AA batteries a year. I know the eQ-3 fail open, not sure on the Energenie, the eQ-3 only shows target temperature, the Energenie also shows current temperature, so in the summer I will check on room temperature to see if I need to turn on the AC unit. Since using an Energenie socket likely I could use IFTTT to automatic turn it on, but never bothered.

Personally although EPH wall thermostats can link master/slave with OpenTherm, I would not fit zone valves, I would use programmable TRV heads, on my top floor I have 4 bedrooms, however one is now an office and one a craft room, with TRV heads I can program them to heat two rooms in the day and two rooms at night, zone valves in the main are not that flexible. So with zone valves you end up heating a whole floor because one child is in a bedroom doing home work, with TRV heads you can just select that room.

I don't really know why you're going to all that bother. It seems wildly over complicated and expensive to zone each room using 2 port valves and individual stats when simple TRV's and manual control or more intelligent wireless E-TRV's controlled by a wireless router and app could be used.

Much simpler, cheaper, easier to install and much easier to maintain.

Simple TRVs don't do anything other than balance the radiators badly, they don't allow for different temperatures in different parts of the house at different times of the day at all, which is what I'm after.

The powered TRVs aren't a very good solution, they're handy if you want to zone every room without ripping all your floors up, but having the thermostat low down at the bottom of the radiator means they will tend to reach temperature too quickly and that effect will dissipate as room warms up, so they can't simply be offset to get the right room temperature.

They also require a powered TRV on every radiator, so that's 14 required in my relatively small house. Compared with 3 valves and controllers, there isn't a cost benefit, it's unlikely to be less maintenance if there are 14 batteries to look after, it's going to be more problematic to install if you have to run power to each radiator instead. And it's a worse system.

All I'm doing is zoning each floor, which is a Building Regs requirement for new builds anyway isn't it? The only extra beyond that is zoning the top floor into two as one of the rooms has a completely different use profile to the rest of the house and that's trivial given it's all new plumbing and wiring.

paulrockliffe said:

Simple TRVs don't do anything other than balance the radiators badly, they don't allow for different different temperatures in different parts of the house at different times of the day at all, which is what I'm after.

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The cheap eQ-3 heads will allow different temperatures in different parts of the house at different times of the day, but they don't balance the radiators the lock shield valve does that. OK there is one brand where the lock shield valve and TRV is combined.

paulrockliffe said:

The powered TRVs aren't a very good solution, they're handy if you want to zone every room without ripping all your floors up, but having the thermostat low down at the bottom of the radiator means they will tend to reach temperature too quickly and that effect will dissipate as room warms up, so they can't simply be offset to get the right room temperature.

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eQ-3 heads do have an off set, and the radiator causes the air in the room to circulate, so monitoring air temperature at the bottom of a radiator is likely the best position, I can say since I have nine electronic TRV heads, that the only room with a problem if you can call it a room is the hall, where the air does not circulate due to height of ceiling being on the next floor on the landing, all other rooms setting to 20°C gets room to 20°C +/- 0.5°C

paulrockliffe said:

They also require a powered TRV on every radiator, so that's 14 required in my relatively small house. Compared with 3 valves and controllers, there isn't a cost benefit, it's unlikely to be less maintenance if there are 14 batteries to look after, it's going to be more problematic to install if you have to run power to each radiator instead. And it's a worse system.

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14 radiators = 28 AA batteries, however the bluetooth eQ-3 can be set in groups up to 5 in a group so if more than one radiator in a room all will work together.

paulrockliffe said:

All I'm doing is zoning each floor, which is a Building Regs requirement for new builds anyway isn't it? The only extra beyond that is zoning the top floor into two as one of the rooms has a completely different use profile to the rest of the house and that's trivial given it's all new plumbing and wiring.

Click to expand...

It depends on who's interpretation is used, some LABC publish on line PDF documents which state a simple TRV head is considered as zoning, clearly using electronic TRV heads is zoning, and it is only required with new build anyway. What is important is how the boiler works, my new house with oil fired boiler which is simple on/off zones work without a problem, but with gas condensing modulating boilers there are two ways to control the boiler, one is the return water temperature, the other is connection to the ebus, with boilers which can use opentherm as I said EPH do linked thermostats, but some boilers force you to use their own modulating thermostat or don't have the option to use a modulating thermostat, so your forced to use a single thermostat.

The on/off thermostat is not to control room temperature, it is there to stop the boiler cycling on a warm day, if you use an on/off thermostat to control a room temperature it will result in the return water temperature not stabilising, either a modulating wall thermostat or a TRV is required to control room temperature when the boiler needs to modulate.

Have a look at your boiler specs and the heatloss figure for your office room- if the boiler can't modulate down to the kwh required to heat that one room on its own in the daytime it may start cycling frequently (which is inefficient and could accelerate wear and tear damage to the boiler). You might find it is more cost-effective to chuck an electric convector in that room & stick with 3 heating zones ( remember you can reclaim costs for operating your home office on your tax return )

I think @ericmark beat me to it and explained the approach very clearly. E-TRV's can happily work individually or together & via a router and there are various apps that can control individual spaces and use sensors in every room to control the air temp well away from the rad itself, even manual TRV's can control individual spaces but that takes a fair bit of manual intervention but that's another story.

If you are happy with thermostats and 2 port valves then that's fair enough. Controlling 1 or 2 radiator(s) in one room via a 2 port valve and their own thermostats is kind of a sledgehammer to crack a nut approach IMO. Shutting off all the rad valves in the house except the one in the office and then set the temp in that room using a phone whilst in the room, I would find much slicker.

If you are happy to install and control the system via 2port valves and individual control then of course that is a way of doing it. Whether it's a better/more exact/more cost effective way of doing it is another question.

You'll be hard pushed to get a better valve than a Honeywell as @oldbuffer suggests.

14 radiators in a relatively small house or would that be 7? Some may say that changing 14 batteries ever year or 2 is easy compared to replacing syncro motors or full valves if needed.

A bypass is set as a mechanical device within the system, you wouldn't be able to set a normal bypass valve to open an electrical valve. There may be a way using pressure/flow sensors to activate a switch to control it but that would have to be a hybrid system I would think.

I will admit when I first converted my mothers house to using electronic TRV heads it was not as good as expected, however it was just a case of adjusting to get them to work.

I will explain, the radiator should be set so the return water is at around 40°C so the boiler can extract the latent heat, if the lock shield valve is set, then the TRV head works well, however there is some laziness on the part of some installers and they don't set the lock shield valve, this is specially bad if the TRV is on the return, what happens is the heating starts the radiator gets really hot then the TRV closes but it takes time for the radiator to cool so the room over shoots causing a high hysteresis.

I did not have thermometers I could put on the radiator pipes, but the TRV showed both target and current temperature, so once the heating had been on for a while so stabilised, if current was above target I closed lock shield a little, and if below then opened a little, once set the temperature stayed spot on, the only problem was the TRV had rather too much anti-hysteresis software, and when the temperature in morning went from 16°C to 20°C it would get to 18°C fast, but from 18°C to 20°C it slowed up, so I set it to go to 22°C for an hour then back to 20°C this was with Energenie heads, I am told the Drayton Wiser heads work out the time taken, and adjust themselves so it can reheat a room faster.

Now when we sold my late mothers house the buyer did not want the smart TRV heads, so they were removed and the old mechanical TRV heads replaced, it was found they now worked very well, as now the lock shield valves were set, so had they been set in first place likely would have never fitted the electronic TRV heads.

With this house we don't have gas fired boiler, it is oil, so it is not so important to control return water temperature, however we do have rooms only used every so often, I found the cheap eQ-3 heads actually work better for me than the expensive Energenie, the big thing is I can set the Eco and Comfort setting to what I want, so the Eco is set to 17°C and comfort to 20°C and twice a day with rooms not normally used the temperature is set to change between 16°C and 17°C this means if I forget to turn the room down it auto turns down at those times, when I come to use the room I press the eco/comfort button on the TRV head and room heats up. For rooms like bedrooms they are set to heat at night, and kitchen during the day etc.

They work well, I use the bluetooth version it makes setting up easier, I paid £15 each, the non bluetooth I have seen for under £10 each, but the main point when using gas boiler is the TRV is analogue, it slowly opens and closes, and the boiler is analogue it slowly raises and lowers flame hight, but the old zone valve is digital i.e. on or off, it does not gradually open or close, so is simply not any good to control temperature with, yes on a time switch so an area is heated only at set times, but if you try to control a zone valve with a thermostat then the very cleaver boiler software which turns the boiler flame hight up/down to gain the latent heat will be defeated, it will still heat the home, but not in an efficient manor.