21 Jan 2023
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United Kingdom
I just moved in a 4 bed 3 bath 80s built house which doesn't look like anything has been done to it since it was built. I have been reading about heating systems and think I have a vented system with regular boiler. There are 2 tanks in the loft which look like a large cold and small header. The boiler has one flow and one return, a valve splits the flow into (I guess) the central heating and into a tank on 1st floor, which also has (a backup) electric immersion heater. There is a single Grundfos pump. I wanted UFH but the cost and disruption has pretty much put me off it. We are planning to convert the loft, and a small ground floor to replace an unheated conservatory. Ground floor rad pipes are in the screed. We only need a toilet in the loft, not a shower. Plan is to move the cold and header tanks to a corner when converting the loft.
Q1. I guess toilet and basin could be fed by mains cold as that is in the loft for the cold tank, could we get hot up there given the cylinder is on the floor below? A pump?
Q2. As the existing heating has a pump, should it be possible to extend the system to the loft?
Q3. There are 3 showers, am I looking at 3x power shower pumps? We want concealed rather than shower box units.
Q4. Any suggestions on extending central heating to the group floor extension given the existing pipework is in the screed?
Q5. Could we have vented heating with header tank, indirectly heating an unvented pressurised hot water cylinder to remove the need for the cold tank, and run hot to the loft basin?

Massive post, if you made it to the end then thank you!
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First job is how good is your water supply at the house- Ltrs per min and dynamic pressure. Unvented cylinders want min 20 Ltrs/min at 2 bar dynamic...

Q1 If you've got room in the loft for header tank for conventional dhw and the bottom of the header tank is above your washbasin - ideally a metre above- then yes you can have hot water in the loft, no pump needed.
Q2 long as the bottom of the f & e tank is above the top of the loft radiator (500mm min, a metre would be better) you can have rads in the loft.
Q3 3 showers on your existing setup might empty the cylinder a bit fast (if it's std 150ltr). Put a 300l cylinder in with a single boost pump at the larger cylinder (lots of detail here- type of flange, cold water feeds from the header tank) should work ok.
Q4 If you're replacing the conservatory with a proper extension then yes extend rads in there. If the copper in the screed hasn't been wrapped or ducted you are right to be concerned. Easiest may be drops from the first floor 22mm trunks.
Q5 Yes. Check your water supply. If you're planning on renewing the boiler there's no law against a combi running a cylinder (vented or unvented)- use the combi dhw in the kitchen and downstairs shower, use cylinder for the other 2.
Thanks for the quick response and clear answers!

Q1, Q2 aim was to put the tanks in the eaves, meaning they would be below both rads and basin in loft. I will need to test the water pressure and flow, a water softener sales guy who used to be a heating engineer estimated it was 'good' and 22l/min+ a couple of days ago. Aim is to have an electric hot water tap in the kitchen sink, washing machine would be using main hot water supply though.

Q5 can you have vented unpressured space heating system and unvented mains pressure hot water system running off a regular or system boiler? I am wondering if the feed to hot water tank is simply switched from cold tank to mains, removing the need for power shower or pump and getting hot water supply to loft. This wouldn't get rads into the loft though, which I guess is why you suggest a combi? I think using a combi would require pressured CH system and would potentially cause leaks in old pipes?

Q4 I just pulled up some carpet and took this photo of the pipe in screed, does this look like the type of wrapping you are talking about? Would this make digging out some screed to connect the extention rads to existing downstairs a better option than routing down from 1st floor? I will be getting a heating engineer to do all the work but want to try and avoid regrets from doing work based on a single opinion.


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Your pipes- it looks from the pic as if it's been coated with something but I can't tell what. No visible corrosion where it drops into the screed (which is a good sign).
Boiler options- yes modern boilers (system or heat only or combi) can run pressurised which would solve your loft radiator problem. If there are 'weak spots' in the pipework, now would be a good time to find them?
Combi was more to do with spreading the dhw load than running pressurised. Depending on the layout of the house you could do something similar to my setup (combi looks after kitchen, utility room and ground floor shower, cylinder looks after both upstairs bathrooms). Combi and cylinder do not have to be mutually exclusive.
Yes the primary of an unvented cylinder can be connected to an open vent heating system. There are limits to where you can put unvented cylinders- pressure relief pipework is required.
Disadvantage of the unvented- yes it's mains pressure cold water in, mains pressure hot out. If the mains pressure turns out to be not up to the job your options are limited.
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Thanks a lot for the detailed replies, I think I now understand! Plan is to fit a new, higher, F&E tank in the loft to allow rads in the loft, replace whole ground floor with UFH and leave 1st floor as rads. Will remove existing vented cylinder and cold tank and replace with megaflow or similar mains pressure hot water cylinder. Next step is to get a plumber to do it, and potentially replace all pipework to hot and cold outlets, if needed. I am thinking/hoping that this mix of vented CH and unvented HW will work. Will get pressure tested before starting, water softener installer chuckled and classed it as "well good", even with the stop cock half open.

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