Efficiency:- LPG Combi v. LPG instantaneous Water Heater

[Veequest]

Its time to change the old combi oil boiler, so the preliminary research has just begun. (for 2 bed cottage, 1 shower only at a time, only 2 adults in residence generally)

My other half asserts that a multipoint water heater is more energy efficient because the heat exchange is direct ie flame to pipe/plate, as opposed to a combi where heat for dhw is indirect. I can't find any published ratings (like sedbuk) for water heaters to verify this.

Any help with the following questions would be very much appreciated.

1, Is this the case? & is the efficiency difference significant?
2, Do some combies exist that also have a direct heat exchanger for the dhw and if so which ones?

Many thanks[/b]

 

[dcawkwell]

Since it is a 2 bed cottage.
I would swap to an lpg combi with 4 lpg 47kg bottles as I expect heating costs aren't that great.
An lpg combi will be cheaper to install, more compact and quieter.

No point in an lpg water heater. No saving.

The oil combi will have a much faster water delivery but does keep a 50 litre store of hot water ready to go to achieve this and you need the big oil tank.

 

[Boilerman2]

Unless you fit a Bulk storage LPG Tank you will find an LPG system very expensive to run! we have taken out a few LPG combis and replaced with an oil fired combi (Grant vortex 21e)

47Kg cylinders cost around £70-80 each, and you will go though 4 -6 per month!!

 

[gasanstuff]

An Intergas is direct flame to pipe/heat exchanger as you put. and can be fitted on lpg

 

[Veequest]

Thanks for the advice, we would put in a bulk tank as the thought of lumping 47kg cylinders up the path several times a year (let alone a month) is not practical & as the house needs more insulation (still ongoing) thats a lot of cylinder movement. It's drafty as we are on the coast in far NW Highland where a howling gale is the norm. Could replace old oil boiler like for like but cons for oil are - noisy, big, heat up water even when not being drawn (which kind of defeats the object as far as other half is concerned, he loved the old nat gas instant heater we had at previous address because he got it 2nd hand for 20 quid & it never broke down!) In addition the oil tank is being moved anyway so could put in lpg at this juncture.

Pros for Instant multi water heaters:- zero hot water storage, direct heat exchange & longevity of the units.
Therefore he is considering the option of a water heater plus a heat only boiler (as opposed to a single combi). I would like to find out if that would actually be more energy efficient & then if so try to work out how many years to recoup the extra initial costs.

So once again any thoughts & comments would be much appreciated. In the mean time I am checking out the Intergas Combi (thanks for that tip)

 

[dcawkwell]

Combi boiler.
Absolutely no benefit in have a water heater.

Thanks for the advice, we would put in a bulk tank as the thought of lumping 47kg cylinders up the path several times a year (let alone a month) is not practical & as the house needs more insulation (still ongoing) thats a lot of cylinder movement. It's drafty as we are on the coast in far NW Highland where a howling gale is the norm. Could replace old oil boiler like for like but cons for oil are - noisy, big, heat up water even when not being drawn (which kind of defeats the object as far as other half is concerned, he loved the old nat gas instant heater we had at previous address because he got it 2nd hand for 20 quid & it never broke down!) In addition the oil tank is being moved anyway so could put in lpg at this juncture.

Pros for Instant multi water heaters:- zero hot water storage, direct heat exchange & longevity of the units.
Therefore he is considering the option of a water heater plus a heat only boiler (as opposed to a single combi). I would like to find out if that would actually be more energy efficient & then if so try to work out how many years to recoup the extra initial costs.

So once again any thoughts & comments would be much appreciated. In the mean time I am checking out the Intergas Combi (thanks for that tip)