Over-sized boiler?

[theprof]

Hi, I'm new to the forum, and hope someone can help.

We have an ageing (30 year old) Ideal boiler in a house we recently bought and would like to replace it with a 2004 Potterton Paramount 80 from a swimming pool we are taking out of service. The Paramount is in good nick and hasn't been used very much.

The old Ideal has an output of 115,000 BTU/hr which is about 33kW. The Potterton is max 80 kW but modulates down to 20 kW min.

The 6 bed house has a max heat requirement of about 37 kW according to my whole-house calculations and those of a recent installer who went round.

It's a vented system with a hot water cylinder.

The installer says the boiler is too big, and Potterton tech seem to agree. I really don't want to chuck it out, and need to know why. Firstly the boiler can be set to max out at 40 kW in software, but I agree the min output is still 20 kW. However the existing one is blasting away at 33 kW all the time, so...

Any advice gratefully received.

 

[mylesy]

if the boiler was 2004 its most likley non condensing, you should really install A rated only now. you can pick up combi boilers or system boilers or even heat only boilers for as low as £450. and it will be more suited to the output you need. its good having boilers to re-use but some times its just not practical, and youll save anyway on an a rated for obvious reasons. and youll also get warrranty it will be new so will be a while before things go wrong so on and so on. you can range rate older boilers though, youll need the manufacturers instructions to know what to set all the pressures too. you can probably get them online somewhere but id get a new one.

 

[theprof]

Thanks for the advice. The Paramount is a condensing boiler, though, with A-rated performance.

 

[doitmyself]

The 6 bed house has a max heat requirement of about 37 kW according to my whole-house calculations and those of a recent installer who went round.

37kW sounds a lot even for a six bed house - unless its very old with single glazed sash windows, solid (no cavity) walls and no loft insulation.

Did you use the Boiler Size Calculator? It's the most reliable one.

Is the house well insulated (if that's possible)? If not there are plenty of low cost or free offers available. Check out the Energy Savings Trust Grant Search

 

[theprof]

Yes, I did use that one. Tried it again and it still comes out at 37 kW. Big old house, solid walls, loft conversion and not convinced there is much insulation above the ceiling plaster in the loft.

Have considered additional insulation, but difficult with solid walls, although I agree not impossible. Roof also difficult because it involves removing all the ceilings.

 

[franky]

Ok this is a difficult one to explain but I'll give it a go. Try to keep as close as you can to the 37kw because other wise you'll be firing up and then stopping then firing up again after a waiting period. If you have a correctly sized boiler it should fire up get to the right temp and the return should be coming back around 55deg so it then condenses therefore saving you money.

 

[diamondgas]

Well the prof a question if i may. Did the old ideal heat your house okay even in the last two winters we've just had or did it struggle to keep all your radiators hot? Just curious to be honest...

The paramount is a commercial boiler, bye the way. and you'll need a guy with commercial tickets to install.... You'll also need to bring your new installation up to current standards. Is the cylinder currently gravity circulation? If so that needs addressing as well as the house needing zoning and TRV's fitted! All that is minimum requirements I do believe! You may already have this already though!

If it's good advice your after however it sounds like you've been given it from the manufacturers tech department. That's who I'd consult if unsure. Absolutely nothing stopping you from having it installed however apart from the guy installing it wanting to guarantee no come backs. Not so easy with your scenario I'd hazard a guess! :thinking: