New heating system - 130m^2 with 2x power showers

[markocosic]

Evening,

Kid brother is after a new heating system and he's asked me for help speccing it. I'm after a sanity check here!


The house is a 130m^2 Wimpey house built in the late 1980s. Nominally insulated cavity wall construction with dabbed plasterboard, but the detailling is rubbish and it leaks heat like a sieve.

It presently has a "17kW" potterton suprima feeding single panel rads in a single zone (no TRVs but does have a room stat in the hall) and a vented hot water cylinder via two two-port zone valves. One shower via a pump from the HW cylinder and the CH header tank (yes!) and the other shower is electric.

Issues with the current system:
-electric showers are hopeless; two high pressure 12L/min with 5C mains inlet temperature showers are desired.
-the heating is inadequate both in ultimate output and response time; the ability to maintain 20C down to -5C external temperature is desired, and as the house leaks heat like a sieve and is unoccupied for significant parts of the day he'd like a system that allows it to drop to 10C, then can bump it to 20C in an hour or two for the 10 hrs/day that the house is actually occupied.
-one zone heats lots of the house unnecessarily; he'd like two zones; one bedrooms/bathrooms and another "other" zone - upstairs/downstairs essentially.
-the radiator sizing is all over the show and combined with a lack of TRVs means that the room temperatures are all over the show.
-It's a non-condensing boiler/ludicrously inefficient; boiler limits current radiator output but the rads would limit any larger boilers output.


I propose swapping all the rads for "oversize" double panel affairs. Providing that they're all equally oversized so that each room in the zone heats up evenly, am I correct in assuming that there's no problem with this bar the delta cost of the larger radiators?

I propose fitting one roomstat in the downstairs hall; one roomstat in the master bedroom. Reasonable?



Then we have options:

1) One system boiler, one pump, three 2-port valves, a programmer capable of running this lot, plus an unvented cylinder.

2) Two combi boilers with built in pumps etc. Run the upstairs and one bathroom as one zone/"house" and the downstairs/other bathroom and kitchen tap as another zone/"house" with each having their own programmer.


The latter appeals. Thanks to volume, an entire combi with all the gubbins built in costs about the same as an unvented cylinder and all associated pressure gubbins and zone valves.

The labour with the skills to bung in a combi vs fit an unvented cylinder and zoned system boiler is also cheaper. (we can install the water side in ourselves, fit the backplates, then have an RGI in to run the gas and hang/comission the boilers) Plenty more semi-qualified (capable of servicing one brand of boiler, but utterly hopeless at servicing/fault finding a "system" of components) service techs out there too.

The inevitable breakdowns/general servicing are also less of a showstopper, as you'll always have somewhere warm in the house/some hot water.

How daft is this? Seen it done elsewhere?


Concerns:

-Gas supply. The existing gas supply is f**king sketchy. A single 15 mm pipe ~12 metres in length feeds a 7kW heat input living room gas fire, 17kW boiler, and large (10+kW heat input) gas range. If the hob is lit on a low-medium output, it'll be extinguished when the boiler fires. Pipework after meter all needs replacing anyhow, so the options are equal here anyhow. The supplier is arranging a "GT1" test for the gas to see what pressures/flows are available. At the minute it has a U6 meter; U16 would be required for this setup, correct?

-Water supply. The existing water supply to the house appears good. (>24L/min on an open pipe via the 15 mm stoptap and meter, no doubt more when the stoptap is replaced with a large dia MDPE one and the supplies branched in 15 mm after this)

-Boiler *minimum* output in CH mode. To get 12L/minute with 5C input we're looking at large combis. 10:1 modulation is still 4kW minimum output. No problem in winter as the heat loss exceeds this comfortably. No problem in summer as it'd need just a quick "boost" then a low heat loss/some thermostat hysterewsis would prevent the boiler firing too often. Spring/autumn are a concern. How short a cycle is "too short" for a boiler?


I'm looking a pair of Vokera Linea Ones (fitted in the attic space) for around 3k the pair inc sundries at present:

http://www.vokera.co.uk/trade-professionals/boilers/linea-one/

Includes modulating pump, gunk filter, filling loop, weather comp heating control, frpst stat, predictive DHW control for preheat etc - just add water, gas, expansion vessel, and radiators?

 

[Mark Br]

Edit - sorry couldn't be arsed with a full reply

Simple answer is get an RGI who knows what he's doing to advise your brother

 

[markocosic]

Location Sutton Coldfield; advice and quotations for the gas work and commissioning from competent persons - welcome.


Being an RGI/member of competent persons scheme means nothing about their ability to specify a heating system though; the overwhelming majority are just plumbers with gas tickets not heating engineers. Not so much can't be a**sed to specify as can't.

 

[denso13]

So you don't trust the professionals but are happy to trust a DIY forum?

 

[Bunnyman]

Threads like this make me chuckle u really got no idea!

 

[CBF]

you would be better sorting out the insulation rather than this total overkill of fitting two boilers & bigger rads, unless of course you want twice the amount of heat in the street & a vastly increased gas bill

 

[Breesey]

One correctly sized boiler heating correctly sized rads with an unvented cylinder and upstairs/downstairs zones.

A bit of work to insulate the building properly.

A U6 meter delivers 6m3/hour, this should be enough for what you are considering.

And call someone in who knows what he's doing. Your assumption that 'the overwhelming majority are just plumbers...' comment is based on what exactly?

 

[hazetimesfive]

his fellow eastern europeans i guess

 

[muggles]

Seal and insulate your house and get an unvented cylinder installed

 

[swbjackson]

I'd suggest you go elsewhere and ask. You've already put the backs up of the trained professionals here who may have been willing to help. Coming onto a forum and requesting advice from professionals by insulting the entire profession is hardly the correct way of going about things. God help your brother if you have anything to do with dealing with the professionals that he calls in. Faced with that sort of attitude my first instinct would be to walk and if I bothered to quote it would be at twice my normal rate so that if I was unlucky enough to get the job I'd have the comfort of knowing that at least I was making out of the job despite working for a PITA.

 

[Dan Robinson]

this is 130m2? Not 1300 right?

Two boilers?

 

[markocosic]

Exactly that Dan. A pair of boilers on 130m^2 to replace the two existing boilers. (and make the 3rd gas heater redundant/decorative)

Two? One open vent gas system boiler and indirect cylinder and one unvented instantaneous electric boiler for the 2nd shower. Both pretty ****ty. Plus that gas fire for the living room that unfortunately isn't decorative at the minute.


Heat loss calculators say 12kW +2kW to meet bare minimum standards for ability to heat the home. (already has insulated cavity walls, insulated roof, but long/thin building with many windows and poor detailling by late 80s Wimpey homes - that irritatingly average specification that's neither great nor bad enough to warrant tearing the building apart to bring it up to modern standards)

If you want the place warm in current temperatures you need about 17kW. 20kW if you intend to use night setback and only heat the place when occupied, which requires the ability to warm up in a reasonable time. (heat required 0530-0630 and 2100-2300 for bedroom zone; 1630-2200 for downstairs zone) 24L/min on a 40C temperature rise required if instantaneous hot water, else a 300L unvented cylinder to do four showers back to back.

The "majority are just plumbers" comment comes from the above Breesey. As soon as you ask for "not building regs minimum" spec, a G3 ticket, or even zoning I think that the majority of RGIs are out of their depth. State who you're not after and those whose advice has value generally smile knowingly to themselves and emerge from the woodwork.


20-25 kW system boiler, zone valves, and a 300L unvented were indeed Plan A and the U6 would work fine with this. It would be compatible with solar in future too, but the "MCS accredited installer premium" required for RHI eligibility makes it uneconomic at the minute.

The pair of combis came about when pricing up. Combis the same price as system boilers and modulating down to similar levels? Combis the same price as unvented cylinders? Why not fit two and have one doing HW for the shower only. Or even ditch the zone valves altogether and effectively run the house as two flats, with the entire heating system (controls, valves, pumps, filters, 'n all, covered by one warranty from one manufacturer, with a large degree of redundancy for the inevitable breakdowns) No standing losses/loss of interior space, no limit to the draw off, and a CH output for bringing the house to temperature quickly limited only by the radiator output.

Downsides are solar incompatibility and the gas supply as far as I can see. They (plus range and fireplace) would require U16 for when both showers were in operation, but the meter is FOC if the supply will support it; pipework all requires replacement anyhow as the current installation is (dangerously I would say, given that it extinguishes the hob) undersized. Hence price-wise there's nothing in it.


For any interested, I had a chat with Vokera and they were happy to discuss the application. In answer to the specific questions:

Large rads. Yes good, drops flow temperatures especially with weather comp and will reduce cycling. Beware overall system capacity and the need for an additional expansion vessel, and there'll be a delta cost involved here.

Roomstat locations were appropriate. Definitely don't put the upstairs stat in the hall, and avoid outside walls.

I'm not the first to ask about fitting a pair of combis to feed a pair of showers. 130m^2 is certainly the smallest property though.

Minimum output. The minimum output is on par with the smallest of their system boilers. Your minimum is now nominally twice that (8:60 kW modulating rather than 4:20 kW of the smallest system boiler) but given the timing of the zones and it being likely that each one needs 2/3rds of a house worth of heat to heat the zone from cold it isn't quite so bad. The boiler has decent anti-cycling controls and hysteresis/system water content ought to take care of the rest. Watch the first 15 minutes @ 75% output default setting for CH though (set it lower/off) and cap the maximum CH output to suit the radiators that you're hanging off each one. You'd need a larger expansion vessel than the built-in one with a single boiler, but not with two as two zones.

 

[Agile]

I am sorry that you have such a low opinion of those who work in the heating industry. Obviously you know more than most of them do, particularly the ones who left school at 15 as they were academically challenged.

But then you are wanting to do most of the work yourself so there is really little to be done for you by anyone.

Have you engaged someone to do the gas work yet? That may not be as easy as you imagine.

By the way, contrary to what you expect, the boiler mounting bracket should also be fitted by an RGI.

Tony

 

[Breesey]

So you don't want, or need, any advice? You just want to show everyone how clever you think you are.

Interesting that you have a 'kid' brother, you sound like an only child!!

 

[Dan Robinson]

Bonkers.


Just bonkers.

U16 in a what? 3? 4? bedroom house? Fook me.

I bet the OP is a project manager.

The "majority are just plumbers" comment comes from the above Breesey. As soon as you ask for "not building regs minimum" spec, a G3 ticket, or even zoning I think that the majority of RGIs are out of their depth. State who you're not after and those whose advice has value generally smile knowingly to themselves and emerge from the woodwork.

The minimum output is on par with the smallest of their system boilers. Your minimum is now nominally twice that (8:60 kW modulating rather than 4:20 kW of the smallest system boiler) but given the timing of the zones and it being likely that each one needs 2/3rds of a house worth of heat to heat the zone from cold it isn't quite so bad. The boiler has decent anti-cycling controls and hysteresis/system water content ought to take care of the rest. Watch the first 15 minutes @ 75% output default setting for CH though (set it lower/off) and cap the maximum CH output to suit the radiators that you're hanging off each one.

Biggest load of crap I've seen since my customer's dog laid a big steaming one on the carpet this morning.