Hot Water & Central Heating - Primatic Cylinder

[darrel.morgans1]

I have a 3 storey 4 bedroom property where the heating system was installed in 1960 / 70's. Hot water is supplied via a conventional floor standing gas boiler and primatic cylinder, heating is via a single pipe system.

Hot & cold water pressure to the 1st floor bathroom is poor and the one pipe heating system is pretty inefficient

I want to overhaul both hot water and heating but want to do in stages due to the costs. I want to start with a new boiler and updated hot water system (which will include a power shower in the 1st floor bathroom). The second stage will be to install a twin pipe heating system with new rads.

What I want to know is whether this staged approach is okay and what would be the best replacement for the primatic.

Cheers

[John Stumbles]

Given the size of the house I'd go for a thermal store or heatbank system. You'll be able to get rid of the tank in the roof (which is probably also in poor condition - maybe it's galvanised, not properly insulated or covered) and get good pressure for showers without a pump. Thermal stores & heatbanks are expensive but at least you can count the £150+ you'll be saving on your shower pump (plus installation) against the cost.

If you want to replace the one-pipe system you'll be effectively putting in an entire new CH system in the end so I'd seriously consider underfloor heating which is more economical and comfortable, though also more expensive. If you get a larger thermal store with appropriate tappings you can run UFH off it without a separate thermostatic mixing valve.

[Mark]

As the OP was worried about cost I would suggest a cheaper system. A cheap way would be to go for a combi boiler [1] and replace the heating with a two pipe system. However if you like fast filling baths you may be dissapointed with a combi. You won't need any tanks, cylinders or shower pump.

You haven't said how many bathrooms you have. That will have an impact on your choice I would say. Also your mains water pressure and flow rate are important factors. There isn't a one size fits all solution.

You also haven't said what the condition or type of your boiler is. You may be able to keep the boiler and upgrade your central heating to a two pipe system and replace your primatic cylinder with a quick recovery indirect cylinder. With new controls etc. that should give you a reasonable efficiency saving. You could replace the boiler at a later date.

[1] May not be suitable if mains pressure or flow rate is too low. M

[John Stumbles]

I deliberately didn't suggest a combi because of the size of house: if the OP has bought a 4 bed place then I'm guessing he's not living in it on his own or just with a partner but has (or will have) kids or lodgers whose demands for HW will make a combi a PITA. Also, fitting a 2-pipe system will certainly be expensive (in time if he DIYs, or money otherwise) which is probably not the job to be tackling first if he's short of money rather than gutting and re-doing everything.

A pumped 1-pipe system can work reasonably well: not ideal I'll grant you but somewhere in the "ain't broke" region.

[Mark]

I have a storage combi in my 4 bed, 2 bathroom house. Although the fill rate for baths could be better it works well. If space/money was no object I would have gone for a thermal store/heat bank.

Normally good advice but I would guess an upgrade would save money and the planet ;-)

Mark

[John Stumbles]

Don't see how it would save the planet: the 1-pipe system should be no more or less energy efficient than the 2-pipe system. Or am I missing something?

[Mark]

I don't know about the relative efficiences of a 1 pipe vs a 2 pipe system but I believe a modern condensing boiler would not work with a

1 pipe system.

Mark

[John Stumbles]

Don't see why not: hot water out, cool water back, heat lost via radiators in between. It might not work quite as efficiently since a 1 pipe system has an overall temperature drop across the circuit meaning that for adequate output from the rads at the return end of the loop the flow temp has to be rather higher than it would be in a 2-pipe system, and so the boiler's heat exchanger might run at marginally lower efficiency, but we're probably talking in the region of fractions of a percent. AIUI the problem with a 1-pipe system is that the interactions between rads' wrt their control settings is much greater than for a 2-pipe system. Having said that my mum's 1-pipe system (which is the only one I have much experience of) seems to Just Work. Even when I added a big rad with a TRV to the loop it - and the new rad - Just Worked.

[Ed Sirett]

I've got a copy of a modern condensing boiler manual which shows it in use with a one pipe system.

1-pipe does not imply gravity which would fail to work with all modern boilers.