oil combi or system boiler?

Coffeepot1

Hi, my combi boiler is on its last legs and due replacement. A really strong shower is important to me. The water board tell me mains pressure for my house is good? There is only me but in a four bed house. I understand that a combi makes sense for 1 person but a powerful shower flow is really important to me and I understand that system are the best boiler type for this? Would really value some advice on this as I'm going round and round in circles on what to do of the best. To throw something else in, I'm 'considering' getting underfloor heating for two of my downstairs rooms (as the floors need to come up anyway). Not definite re: underfloor heating yet but mentioning now just in case it affects decision. Happy to go either way but just don't know which way would be best. I hear either Worcester Bosch or Grant is the way to go whichever type of boiler I get. Many thanks

matelodave

If you need a powerful shower then you'll need an unvented tank for a system boiler - a loft mounted tank wont give you enough pressure.

So you'll have to make space for both the new boiler and a hot water tank and the associated drains/vents.

Either sort of boiler would run u'f heating although most combi's won't heat water at the same time as providing space heating although that usually isn't much of a problem as most people don't run off loads of hot water for long periods (except perhaps for filling a bath).
Wth a combi you never run out of hot water as it's being heated as you use it although that doesn't sound like a problem for your situation.

Generally u'f heating runs at a lower temperature than rads, so if you are going to have both then the u'f circuit usually has a mixing valve and sometimes it's own pump to reduce the flow temperature.

Ideally you need to plan what you are going to do before jumping in - do your own heat calculations as u'f heating is usually better suited to long term heating rather than a quick boost when you get up or when you get home from work.

The lower flow temperatures mean they can take a lot longer to get the place up to temperature than a red hot radiator (ours can take a couple of days if it's really cold and we let the house get cold, but we have really low flow temps <30-35degrees> as we've got a heat pump)

vic_sf49

I went from having storage heaters, an electric shower and water tank set-up, to central heating and a shower run off a Grant outdoor oil-fired combi boiler.

The only place I could have a boiler installed without fitting a new kitchen, was outdoors, and the space created by getting rid of the water tank enabled me to re-jig my bathroom layout, into something far more practical.

My electric shower's pressure was rubbish, but with the new boiler the pressure was great, and it provided very hot water and heating temps....much better than the pretty new gas fired Worcester-Bosch boiler in my new gaff.

I have no experience of underfloor heating (although I need to research that for my bathroom renovation), and had to look to see what a system boiler was...

Coffeepot1

Thanks for the replies. One of my biggest concerns was not having a really powerful shower and going to the expense of a combi then have 'grass is greener' thinking regards a system boiler and kicking myself for it - big outlay at the end of the day whichever choice it is. Good to know about Grant boilers, that helps my thinking, but sounds like a system boiler has the edge. I have the space for either. Are there any thoughts please on the cylinder side of things, if I went for a system boiler, can the cylinder sit next to the boiler or do I need to have it elsewhere/what type etc - will a system boiler cost me a lot more to have installed than a replacement combi? RE underfloor, only considering this as the kitchen floor is coming up anyway for a damp proof membrane (old house, no damp course) so I thought about UFH whilst I was at it, I have space for radiators if I decide against UFH - in this situation, would there be any benefits to install UFH whilst the floor is up (I take the point re: taking an age to warm but I guess I could keep it on separate timer/on low constant heat?) many thanks

Smiley_Dan

The alternative to an unvented tank, and the most powerful shower option, is to use a pump from a cold tank and the HWC.

But this uses a lot of energy and water so I would steer away if possible.

Silent_Dancer

If you are after a powerful shower then a heat only boiler with an unvented shower is the way to go. Oil combis can do high flow rates as they have heat stores but the water can run cold quite quickly.

Cardew

Silent_Dancer wrote: »

If you are after a powerful shower then a heat only boiler with an unvented shower is the way to go. Oil combis can do high flow rates as they have heat stores but the water can run cold quite quickly.

Not all combi's - even new ones - have 'heat stores' i.e. small internal hot water tanks. These also can be turned off in 'economy mode'.


As said above, if the OP's priority is a powerful shower, then a Combi boiler is unsuitable.