Add to Central Heating System

[hedgert]

I have a house that has been heavily extended but whose central heating is still original (or spec for the original house anyway).
It is a conventional boiler (not sure of the correct term - but I mean not a condensing boiler - it's an open system with a top up tank in the loft).
The system cannot keep the house warm in winter - despite the system being well bled, some radiators are only luke warm and some are cold; and turning on one particular radiator close to the boiler to full, results in that room being excessively hot and radiators upstairs being cold. The only way to get a spread of heat through the house is to turn the flow valves on individual radiators downstairs right down.

One winter when the boiler stopped completely I had a professional in, who fixed the cutout or whatever was wrong with the boiler, and gave some advice on the system overall. His two pieces of advice were:
1 - the bore of the gas pipe into the existing boiler was too small and wasn't feeding it with sufficient gas to allow it to run at capacity - fine - I understand that and at some point can get that changed
2 - the boiler isn't big enough for the house and I need either to replace the boiler with a larger boiler or add a second boiler - his advice. He indicated that it was possible to add a condensing boiler - and this is my question - I don't understand how I could combine a closed system using a condensing boiler with an open one based on my existing boiler without having to set up a second circuit with some of the radiators on it - i.e. relaying all the pipework - which I certainly want to avoid.

Can anyone confirm that this advice was valid (i.e. you can mix the two types on boiler) and explain how it works (the open/closed circuit issue).

 

[nstreet]

what make and model of boiler do you have? how many rads and what size? Are they really old and not as efficient as modern rads?. Do you have trv's on the rads?

I don't doubt the word of your engineer, but being a tight git I would also look at the cheaper alternatives.

It could be that simply blancing your system and the addition of some trv's may well give you a good enough improvement not to warrant the expense. You may also require a system flush to help the flow.

He may be tinking of using the second boiler to supply hw only or zoning the house with the minimum of disruption to the existing pipework.

 

[hedgert]

Thanks for the quick reply - I'll check out the make of boiler at home this evening. The house was originally a 3 bed and has had a kitchen/utility room extension, loft conversion, addition of two bedrooms and addition of two reception rooms. So total number of rads was originally 8 (2 of which were doubles) with two bathroom towel radiators. Post the extension work the house has an additional 7 radiators (1 of which is a double) - so it's gone from 10 (2 dbl) to 17 (3 dbl). The radiators are of two types - an original type which has a castlated surface and a newer type that has a castlated surface and some additional fins on the back.
I've put thermostatic valves on as I've decorated rooms, but probably 2/3 of the house doesn't have valves yet.

 

[ricarbo]

Sounds like you need to balance the system. You can do a search on this forum for that.
To work out if the boiler is big enough, you should really caculate the load, which takes some time, although not actually difficult. You could buy a book, or get someone to do it for you. You could get an approximate idea using the calcuator on th 'Sedbuk' site. Many boilers and rads installed are bigger than needed, presumably because there is only likely to be a complaint from the user if they're too small.

 

[hedgert]

I am very keen to take a less expensive option if there is one!

I've spent a fair while since your post searching through the forum for "balance system" "balance" "balancing" and while I've found a number of responses saying "search the system for balancing" I'm struggling to find a post that actually tells me about balancing rather than suggest I search for the term!

The only concrete advice I've found so far relates to not really needing to balance if you have TRVs everywhere. I don't so I'd really like to understand how to balance!

Can you point me at a specific post or outline the steps?

 

[ricarbo]

Briefly, buy 2 pipe thermometers (plumbers merchant). Check they agree by putting them on the same length of pipe near the boiler.
Put system on. Set boiler to max (82). Open all lockshields and set TRVs to max.
Fix the thermometers to flow and return of each rad in turn,starting with the one nearest the heat source (3 port valve by cylinder?) and record reading. When done close down lockshield to increase temp drop to 10 degres centigrade, and vice versa. Repeat until right. Takes ages.
Pump speed affects this. If too fast, temp difference will be less than 10, so slow down pump.
If when all done for same drop across every rad, you find the difference is more than 10 at the boiler flow and return, then the boiler isn't producing enough heat, or the pump's too slow. Consider extra house insulation.
If rads too big, room will be too hot and you can close down lockshield, leaving spare heat for other rads.
do the same for the hot water cyl if there's a valve to regulate it.

 

[hedgert]

ricarbo - thank you - I have ordered some pipe thermometers and will try the procedure you mention when they arrive. It fits completely given that I have one room with a large double radiator (probably 2nd closest to boiler) which is always far too hot, and I noticed that when I turned its TRV (one of the few rooms with one) down to 0.5 it was still warm in the room and the radiator in the loft room radiator (which I'd never known get anything more than just having the chill off it) became luke warm.

nstreet/ricarbo - I have checked out my boiler - it is a Potterton 80e - which the label says is capable of producing 17.6-23.5 kW (depending on gas pressure ranging from 8.5-14.0 bar). I tried the calculation on the sedbuk site and it suggested 14.1 kW was all I needed.

Is there a way I can calculate/measure/check the input gas pressure? (In my original post I mentioned that the engineer who looked at my system said the input pipe diameter was too small to feed the boiler properly). It looks like the input pipe is a piece of ordinary copper pipe (15mm) - is this OK for the size of boiler/input bar range above?

Not the same thing, I realise, but I watched the gas meter while the boiler was running for 60 seconds and (if I'm reading the meter right) it consumed 0.1 cubic feet of gas in that time. Can I deduce anything about whether the input pressure is enough from that?