Posted by: @jo2255

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Main concern is heat geek numbers dont add up for radiator suitability and 5kw heat pump sizing. 

Agreed given what you have said, although Im still struggling with 7kW for a 2004 140sq m house (mine is 1930s 200sq m, partly upgraded to perhaps 2004-2010 standards, 7kW)

BG seems better value assuming all else is equal.  Have you confirmed they are not fitting a buffer or external controls?  I wonder why Octopus are fitting the Daikin not their own Cosy.  I presume they would not fit a buffer or external controls but worth checking if you are considering them.

The 9kW Daikin proposed by Octopus would worry me somewhat.  Its actually the 14-16kW downrated in firmware (unless they have changed their models recently) so is really seriously oversized.  Personally I wouldn't consider this without a bit more thought! and assurance.  Everything you and the surveys tell us would suggest that the 8kW Daikin, which is actually an 8kW machine at heart, would easily suffice.

@jamespa 

Not considering octopus as I do not agree with their heat loss, in addition they want scaffolding, asbestos survey as well as can only fit maximum 200l cylinder. 9kw would be quite oversized for me.

Incase my heat loss actually does turn out to be lower, the new 2026 vailant plus 7kW units can modulate quite low

Inclined towards British gas. They have confirmed no buffer. Intially they had added a 25l volumiser but later confirm not needed as almost all radiators are going to K2 so water volume isnt an issue. 

Posted by: @jo2255

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@jamespa 

Not considering octopus as I do not agree with their heat loss, in addition they want scaffolding, asbestos survey as well as can only fit maximum 200l cylinder. 9kw would be quite oversized for me.

Incase my heat loss actually does turn out to be lower, the new 2026 vailant plus 7kW units can modulate quite low

Inclined towards British gas. They have confirmed no buffer. Intially they had added a 25l volumiser but later confirm not needed as almost all radiators are going to K2 so water volume isnt an issue. 

 

 

Noted.  I updated my post, probably crossing yours, with some negative comments about the 9kW (actually 14-16kW) Daikin Octopus proposal but seeing as you arent considering it they arent relevant!

A volumiser is fine, but if they dont think its necessary then nothing to worry about.  The Vaillant is a sound machine and the controls very flexible.  

@jamespa 

Thank you. Appreciate your response 

Just curious as to what would happen if I had gone with the heat geek proposal for 5kW plus with no radiator changes(not planning to but curious as engineer by profession and need closure)

Most days would be fine i believe. In my area there were 41 days that would potentially require defrost last year.

So the heat pump curve would be set high and radiators would be running at higher temp.

On a cold day house would just not stay warm and defrosts/dhw reheat would make the situation worse I'd imagine as no backup heater as such on the Vaillant unit

Posted by: @jo2255

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@jamespa 

Thank you. Appreciate your response 

Just curious as to what would happen if I had gone with the heat geek proposal for 5kW plus with no radiator changes(not planning to but curious as engineer by profession and need closure)

Most days would be fine i believe. In my area there were 41 days that would potentially require defrost last year.

So the heat pump curve would be set high and radiators would be running at higher temp.

On a cold day house would just not stay warm and defrosts/dhw reheat would make the situation worse I'd imagine as no backup heater as such on the Vaillant unit

I cant really comment on what might have happened as I dont recall anyone posting about invoking the Heat Geek Guarantee so dont know how it works in practice.

The Vaillant does not, SOFAIK, have a backup heater by default, this is an add on I believe (unless they have incorporated it into their 2026 model - which seems unlikely but is of course possible),  You shouldn't need it though unless the gulf stream fails during the lifetime of the heat pump, in which case you (and all of us) will have more serious issues to worry about than being a bit cold.  Of course some in power tell us that climate change is all a hoax, so none of us need worry about that, but they are mostly billionaires so they dont have to worry at all!