"John Rumm" wrote in message
...
wrote:

I think this house is pretty leaky/poor
u values. there is more to do

That was the point I was making to dribble about modulating boilers. The
fact that the boiler can't modulate from 0kW to full output is generally
neither here nor there since the house will still have some heat losses.

Oh my God, Chav, you really haven't a clue. Most boiler don't go below 8Kw
when up to temp the house will be calling for less than 8kW and then
inefficient boiler cycling occurs with the by-pass valve opening and then
efficiency drops like a stone.

A heat bank/thermals store can trickle kWs into a heating system and no
impair boiler performance, efficiency and longevity either.

One thing a store does very well, is allow very high flow rates of hot
water at mains pressure

Cha, you are getting it.

They were also very good in the days when boilers only ran at high fixed
outputs

They are still very, very good, nothing has changed.

- acting as a buffer allowing the boiler to do longish burns heating the
store, while in turn it fed heat to the house at a slower rate. While
this is still the case, a modulating boiler can make a pretty good stab at
doing this all by itself these days.

A poor stab at it I'm afraid. Modern boilers are designed for the
replacement boioer market, where rads were designed to run at 82C, hence
modulation which is not that effective a sthe boiler makers tells us. Then
TRVs on all rads makes matters worse for the boioetr. When having TRVs all
around best have them fed froma buffer cylinder (thermal store)

The 90%+ SEDBUK ratings on modern boilers assume typical setups and
controls, so even if you can improve on the efficiency and squeeze few %
more out of the system, you need to assess if the extra hardware and
install costs of the store are going to give worthwhile returns.

A boiler can be running at over 100% if set up properly heating a store.

There is a fair chance that in financial terms alone they never will
unless you have huge gas bills.

Chav, you just made that up.

So will you get improvements in comfort or functionality to make the cost
worthwhile?

Most certainly!

Heat Loss:

If a boiler is correctly sized for the heat loss at say -3C outside, when -3
it should run flat out continuously. Few do as most are oversized, then
boiler cycling occurs.

A great thing about a thermal store is that doesn't care how large the
boiler is, as long as the flow and return pipes are sized correctly. If a
house requires say 15kW and a 30kW boiler is coupled to the store cylinder,
it will just heat up faster and still no cycling. A boiler twice the size
of CH requirements directly heating rads will cycle like hell.

Also having the CH and DHW off a thermal store 100% electric backup is
available to CH & DHW, and also a second cheap backup boiler can be coupled
directly to the store too. So, a cheapie B&Q job boiler can act as a backup.
It will last as it will only be used once in a blue moon - so full cheap to
run on gas, 100% backup. Or have both boilers on and zippo re-heat. Great
when there is multiple showers and baths going on.