Can anyone explain CH heat output requirement???

A new boiler may be more efficient, but the energy needed to heat the house is not based on the boiler output, rather the heat loss of the building itself. The only real way to reduce heating costs is to improve the insulation levels.
You could look at alternative heating systems, such as air source heat pumps etc, but you will still have the issue of heat loss. Just to be clear a smaller boiler will not help to any real extent and the costs of fitting may never be recovered through reduced gas bills.

If it is such an issue, then I would look at the options to insulate the building.

 

As Caig says you would still need to generate the same amount of heat to keep the house the same temperature as it is now. Look at insulation, walls, floors, roof any drafts from windows and doors. Victorian house is going to be solid walls search this site for insulating solid walls either batoning or insulated plasterboard will make a huge difference.

 

Hi Mark. It's as Craig says.

Is your boiler a combi? I'm guessing it is since you mention 'keeping the same DHW flow rate'.

In which case, your 105's max 34kW will only kick in when you open a hot tap. And the same applies if you were to replace it with the slightly smaller WB's 30kW - it'll only produce this when demanded of it, and that's when instantly heating cold mains water for your tap.

Also, both these boilers (like all modern HE boilers, I believe) are 'modulating' so automatically adjust their burners to meet the actual demand made on them - a bit like turning a gas hob burner down to 'simmer' once the pan of porridge has boiled. So, in practice, if your 105 is keeping your 17kW of rad demand happy, then it's only producing 17kW - it's turned itself down to suit.

So there is no 'missing' 17kW - it chust ain't being generated.

You probably could get a very marginal improvement in efficiency by turning the boiler's CH output down as low as still heats your house - the cooler the return flow, the more it'll 'condense' - so more efficient. Careful control might gain you - ooh - a couple of extra %... ?

A better way - too late now - would have been to increase the outputs of the rads you replaced last year. This would mean that they'd deliver the same heat output on a slightly cooler flow water temp - again giving more efficiency.

So that leaves, as Craig says, insulation insulation and youknowwhat.

Or a completely different heating system like an heat pump. Worth it, when your current system is near-new? No, surely not.

But you can do a lot with £1k's worth of insulation. If you can DIY this, then you could transform your house's insul value. Eg, lining all your external walls with 25mm insulated p'board will have a huge effect. Making sure there are no draughts coming up through your floor boards would ditto.

Anyhoo, you live in a huge Viccie semi, so you pays your costs

 

Think insulation,HW,CH pipes insulate them where possible,you got supended ground floor, insulation between the joists can help.

 

Better boilers than baxi 105e available.

 

Insulated plasterboard is far superior to battening and in-filling. No cold bridges. High quality insulation, so even a thin layer will give huge results.

The thinnest of this stuff ( http://insulationgiant.scene7.com/is/content/travisperkins/C0597_778056_TECH_0 ) is only 25mm total thickness (15mm + 9.6mm) and has an R of 0.70. The next size up is R 1.2.

Either will make a HUGE difference and will transform your home.

Dot and Dab - it'll be dead easy. Follow some video guidelines, and go for it.

 

Main point You have a combi, the priority of a combi is to heat hot water, therefore the higher the output of the boiler the better the flow rate of the hot water.
So to counter this you need a combi that can be range rated on the heating independently from the water, your old Baxi 105 wont do that, but a Valiant Eco TEC will, as will a Worcester Greenstar Cdi

 

Valiant Eco TEC top of my list.

 

Ah - the 105e ain't a condensing or modulating fellow? My bad...

Chust had a wee look - it basically cycles once it reaches max flow temp, turning off for 3 minutes to prevent too much cycling.

Realistically, still not worth him swapping sooner rather than wait until it simply packs in?

 

Just insulate the external walls. The internal walls aren't dragging the room's heat anywhere.

 

Heating setting range output is adjustable, for an example on a ecoTEC exclusive 835, it's 4 - 25Kw.

 

1. The lowest model is actually the 24kw Ecotec Pro
2. The flow rate depends on the water pressure, size of feed pipe from the mains etc, not the size of boiler
3. A higher output boiler will just give you hotter water for the same flow rate.
4. If you are happy with the hot water flow rate and temperature, there's no point installing a higher output boiler
5. The boiler output required for CH is normally lower than that for HW, so it's worth getting a boiler which can be adjusted to give a lower CH output.

 

Mark, I dont know which area of the country you live, but if and when you decide to replace your existing boiler and are happy with the Valiant, have a look on the Vaillant Advance website for an installer. We "Advance" registered installers can offer extended warranties on the boilers because weve been trained to install them as the manufacturers want them installed and commissioned correctly.

 

A new boiler will modulate the heat load depending on the readings it receives from the sensor within the boiler on the flow and return pipe work. So a new boiler may start output of 24Kw then is would modulate the range down and up when required.

Insulation of the house would be advised to help with the heat loss.