sizing boiler - two boilers?

[virgilns]

Just looking to spec a new boiler -

1910 solid brick 3 story (built like that) semi about 250m2 insulation being installed betwene floors and in roof space as renovation progresses (no insulation currenty!). All good sized rooms (benefit of old build!)

2 reception rooms
kitchen
hall

5beds over two floors,

en suite bathroom with shower (used 4x daily)
family bathroom (bath used daily)

Happy to calculate heat loss for boiler size but how do I allow for unvented cylinder?

megaflo, santon, OSO all seem to have 20kw coils.

Telford has 16kw but can be doubled to 32kw high gain coil to reduce reheat time.

If I spec a boiler for the heating and add on the DHW coil I get a HUGE boiler that'll be totally inefficient in the summer, surely??

Could two smaller boilers be cheaper in the long run? one for DHW and one for heating, or do I just assume that the unvented cylinder will not really impact on the heating requriement as it'll be short bursts??

Any help greatly appreciated.

 

[dcawkwell]

glow worm ultrapower boiler and unvented and combi all in one will outperform a 300 litre unvented. All in one nice box.

 

[virgilns]

Preffer a more modular solutionso if anything packs up its easier to get generic bits. I have concerns about the oso for that reason(more cylinder specific components). Not sure I'd want to chuck a boiler and cylinder in together...

 

[Dan Robinson]

Have you asked any professionals to site? What have been their suggestions?

What is the pressure/flow into the building?

Agree a separate boiler and cylinder are a better solution for you. DC seems to have a thing for the Ultrapower - not that on paper it isn't a good piece of kit .

 

[virgilns]

Have you asked any professionals to site? What have been their suggestions?

What is the pressure/flow into the building?

Agree a separate boiler and cylinder are a better solution for you. DC seems to have a thing for the Ultrapower - not that on paper it isn't a good piece of kit .

Yes, but to get a quote or anything resembling a quote seems to be impossible. last one i had round was before christmas and still waiting after chasing a couple of times. I mentionned Wourcester and they liked the boiler but weren't sure if they went big enough for the property...but they go up to a 40 (which should be plenty enough??)

I've found that as soon as you ask people to think creatively, they back off as they'd (totally undrstandably) want the bread and butter walk in 'generic' boiler and off they go...

Pressure is good, 8 bar static and off the 'cup scale' (32mm mains upgraded).

So I really want to know what I shoudl be looking at size wise...the question is, how do I calculate the additional heating requirement for the DHW ?

 

[Dan Robinson]

You've asked the wrong people. Although I confess to being a bit slow with paperwork myself.

As a rule its not worth panicking over hot water allowances with a boiler and unvented cylinder. Just add a few kw onto the house total. Your control regime should cope.

Without seeing the house, and depending on the location of everything I would be looking at an Atag Q38s with a 250 litre cylinder possibly with a twin coil.

 

[Congreave]

I would second the ATAG Q suggestion, size it for the heat loss of the house and ignore the size of the HW Coil. The boiler works on HW priority and you wont get a domestic cylinder with a coil over 20 odd KW.
At a guess go for an ATAG Q38S with an ACV Smartline Tank and dont use ATAG's controls or you'll get a headache. Run the HW straight off the boiler with a sensor and split your heating up with Honeywell S-Plans.
Call Atag Heating and get them to recommend an installer in your area

 

[virgilns]

Runnign the DHW off the boiler would requrie a combi?? or have i missed a trick? Not keen on combi's. not even that keen on a system boiler...Want a standard and a tank (looking for a nice big fat store of water)

Atag is 1800quid which also pushes pretty far above what I was hoping to pay for the boiler. Is it really worth it that much above a woucester or a viessman?

Out of interest, why recommend a twin coil tank? spoke to a manufacturere yesterday and they said that it coudl be counter productive to run the coils in a solar tank in series...is there another reason?

Cheers for the input though - good to hear all the suggestions

 

[Dan Robinson]

No one is suggesting a combi.

The cylinder is heated off the boiler same as rads are.

Vaillant and Intergas are also worth considering before Worcester.

Pay peanuts get monkeys. Don't think about what components cost. Set your budget for the job and get the prices for the system you decide is best based upon n the various advice given. If you have a couple of quotes close to each other, then that's the price point whether you like it or not.

Another phrase I like.... Champagne ideas. Beer money.



Running a twin coil gives faster reheats. But its not worth doing unless you cf control it with hot water priority.

 

[Agile]

The energy efficiency advice on boiler sizing recommends just 2 kW for heating the hot water cylinder.

The reason this works is because the hot water is heated at different times from the heating when all the boiler power is available for the cylinder.

In any case the full boiler power is only needed for heating when its below freezing outside.

It needs calculating but your house is likely to need an 18 kW boiler if its being properly insulated. But do the calcs!

If four people then rule of thumb gives a 250 li cylinder but I would recommend a 300 li as cost is little different and it gives a little more stored water.

Tony

 

[bolshy]

With mains water flow like that, why haven't you considered a thermal store?
Your heating requirements could be met by a smaller boiler.

 

[Congreave]

The Atag is worth the money, the quality is really good but pound for pound I reckon an Intergas 36/30 Combi is best value if you're doing it on a budget.

Site the boiler near your kitchen sink or a shower room and use the combi HW for one specific HW outlet. Then use the Heating Flow and return on an S Plan to do your heating and HW zones.
Using the Combi HW for a shower room will mean you can fit a smaller cylinder for the other HW loads.

 

[virgilns]

Cheers guys. so the Worcester is not getting good vibes...was only thinking this route as I'd been advised Veissman or WB.
Will look at the Vaillant and Intergas as well.

Will do the full calcs tomorrow night when my brain is working again - been a long day at work!!

Thermal store and combi's...thanks, but not for me ta...i've got a specific location for my boiler and tank and it can't go in the kitchen for man reasons.

So house plus 2kw for DHW. Perfect!

 

[Agile]

The Atag is worth the money, the quality is really good but pound for pound I reckon an Intergas 36/30 Combi is best value if you're doing it on a budget.

A combi when he has a shower room and a bathroom ???

Nor does he say that he is working to a tight budget. In fact planning a heat only boiler and an unvented implies he is doing it correctly without any intention to skimp the job to save money!

Note many of the whole house heat loss programs do include the 2 kW for hot water in the output figure.

Tony

 

[mickyg]

The energy efficiency advice on boiler sizing recommends just 2 kW for heating the hot water cylinder

its outdated and stupid. Wouldn't add anything for hot water, just set the system up for the 21st century.