Upgrading CH to per-room control, removing the facehuggers

[very_pointy_ears]

Hi,

Firstly, please forgive the long post. I was never any good at precis at school.

I am doing some renovation work in our house, part of which involves an upgrade to the central heating control. The current setup is an oil-fired boiler (no mains gas here) with the radiator feed being only what I can think to describe as a pair of facehuggers in the airing cupboard before it goes out via a random mix of 8mm and 10mm microbore to the rads:

The boiler is pretty old and right now we can't afford to replace it:

Now ... although the heating system works, it's ridiculously expensive to run, in part because there's only one thermostat for the entire house, and being as it's quite a spread out and extended 1850s house with 2ft stone walls and a great variation in temperature between one room and the next there's no obvious place to put a system-centric thermostat. The result is that either my wife ends up smuggling peanuts or the boiler runs far more than it needs to and burns up loads of oil.

My plan:

• thermostat in each room
• replace facehuggers with up to date manifold
• each manifold outlet has its own valve controlled by that room's thermostat
• any thermostat demanding heat fires up the boiler
• no hot/cold mixing, as this is for radiators not underfloor heating
• a bypass valve a bit like this one between the manifolds: https://www.screwfix.com/p/straight...odFawJFA#product_additional_details_container to maintain flow through the boiler in case only one or two rads demand heat and there isn't enough flow to keep the boiler happy
• I have looked at various manifolds, and these seem as reasonable as any: http://emmeti.co.uk/products/heating-manifolds/t2-topway-fm/

All of this of course would also benefit when we do replace the boiler with something not signed off by a triceratops.

So, I have a few questions/thoughts

1. how much flow or perhaps pressure differential should I allow for with the bypass valve?
2. is the bypass valve I have highlighted going to flow enough, and if so what pressure should I adjust it to? If not, I could install a couple in parallel unless there's a better one. The Honeywell one seems quite expensive.
3. the Emmeti manifold's electrothermic actuators allegedly take 2.5 minutes to respond. For a radiator system that seems to be to be adding a lot of lag to the response, so I wondered about using these instead http://emmeti.co.uk/wp-content/uploads/2013/06/TPG-Motorized-ball-Valve-Modulo-Compact-Oct-2012.pdf though they still seem to take 60s to actuate
4. I heard that using ball valves in a CH system was a bad idea because of rust causing wear on the nylon seals, so wondered about adding one of these: https://www.screwfix.com/p/adey-cp1-03-00022-01-2-magnetic-filtration-22mm/49961

Sorry I've gone on a bit, but there's a lot to cover, and I've been on the home brew. I'm not sure which is worse.

Any comments or info most gratefully received.

Cheers,
Kingsley,

 

[very_pointy_ears]

Oh, forgot to add - I was wondering about the feasibility of a constant pressure pump (if such a beast exists) so that the pump can adjust it speed according to demand. The water heating is (for the moment) gravity fed.

 

[copea]

Honeywell Evohome would do what you want, better and cheaper than what you propose.
Yes, a bypass should be fitted. The one you have linked to is suitable.
A system filter is not needed until you change the boiler.

 

[D_Hailsham]

1.how much flow or perhaps pressure differential should I allow for with the bypass valve?

This is determined by the required flow rate and the pump setting. See the attached DU144 Installation guide.

The bypass doesn't go "between the manifolds". It is connected between the flow and return after the pump and before the manifolds.

is the bypass valve I have highlighted going to flow enough, and if so what pressure should I adjust it to? If not, I could install a couple in parallel unless there's a better one. The Honeywell one seems quite expensive.

You will only need one bypass valve. The Honeywell valve is not expensive; the one you suggest is cheap.

Instead of using actuators or motorized valves, use electronic TRVs on each radiator as in the Evohome system.

 

[very_pointy_ears]

The Evohome system looks brilliant. My main reservation with that is that it's wireless. We've got 2ft thick stone walls througout our house, so unless the wireless has a very large range, it's unlikely to reach everywhere it needs to.

We have to have 4 wireless access points around the house so that we can get wifi everywhere.

 

[very_pointy_ears]

I've emailed a Honeywell connection specialist. We'll see what he says about the walls. Our internal stone walls are topologically equivalent to a "+" sign with rooms in each of the four quadrants, so the signal needs to be able to penetrate these effectively.

 

[very_pointy_ears]

The Honeywell connection specialist said that if we have trouble with normal wifi coverage throughout the house then it's likely that the same issues will affect Evohome.

They offered to send an engineer out to do some signal testing but wanted £75+VAT for this (understandable). Given that I'm reasonably sure that such a visit would reveal that it would indeed be a problem and therefore the Evohome system wouldn't work reliably here, I'm unwilling to pay for an engineer to come round. I am therefore going back to my original plan.