advice on oversized oil boiler

[1737021225]

Hi, so our house has a heat loss of about 6kw, (1950's semi, about 100 sqm) but the old oil boiler is a grant 15-26 kw external oil boiler. it's not been in use since we moved in, and is currently disconnected as we removed the old vented hot water system and want to replace with unvented in a different location.

As far as i can find out this oil boiler can't modulate its output meaning that at a minimum it's 9kw in excess of the required heating load (and that heat load is at a dT of 21 afaik, which is only the coldest parts of the year).

The boiler may also be factory set to closer to 20kw output but i don't know.

What could i do to try to make this work better? i would expect it will short cycle, so would adding a pretty large buffer tank help?
In theory it would take between 20 to 30 mins to heat a 100l buffer tank from cold (dT 40C), depending on whether it is actually delivering 15 or 20kw.
this is all new to me, i only found out what buffer tanks did about 5 mins ago so i have a lot to learn about heating systems so value any input.

P.S. eventually i might switch to a heat pump so would like to design a compatible system for that in the longer term.

 

[muggles]

Why not go for a heat pump straight away? You'll probably need to take the buffer out when you fit one so it's a bit of a waste of money to do that now only to throw it away later on

 

[Razor900]

Your could replace the unvented cylinder with a thermal store or heat bank and take the heating supply from that to allow longer firing times.

But then when you need to upgrade the system again that configuration will almost certainly not be the best.

You could fit a TPI thermostat but that could well lead to the boiler condensing internally which you really don't want.

Which is all a roundabout way of saying you should probably decide what system you will need in 5 years time and plan for it now.

If you making significant changes to the heating system I would certainly advise you go for one which will enable low flow temps which will give you the option of going for either oil or airsource.

Sapphire do make a fully modulating oil boiler but @muggles is the expert on them and an agent for the company

 

[muggles]

I think even a Sapphire would cycle quite a lot here, not to mention they're quite expensive to buy. I think the money would be better spent on a heat pump unless upgrade works are prohibitive

 

[Exedon]

As above if you're going to with a heat pump just go for it.
You can easily re jet the burner down to 15kw from memory it's a .45/80°EH nozzle needed 8 bar pump pressure you may need a disk on air intake.
We have got a couple of the small Grant's running on .40/80°EH nozzles on small systems.