New boiler sizing advice

Londonjoe

Hi All,

I have a dilemma.

I've just moved into a fairly large semi detached house (2,000Sq ft).

They have a system boiler in the laundry room and an Aristan water tank in the pantry (connected immersion heater). The house has 7 radiators downstairs and 9 radiators upstairs with three toilets and two baths/showers.

At the moment we have a Glowworm 24 Hxi boiler (installed 2008) and with 1.5 hours in the morning and 3 hours use in the evening, received a bill for £200 for the gas for one month.

I suspect the heating system isn't working efficiently and so have had various engineers in to give me quotes. The advice received varies considerably from being told to fit a combi boiler for hot water on demand (the system I'm used to coming from a small terraced) to fitting a new system boiler (Valiant 937).

The advice on the size of the boiler has varied considerably and differs per engineer, with some saying the boiler is the right size to others stating it's too small.

It takes one hour to heat the house properly but the it never warms to above 17c.

Any advise on sizing would be appreciated. I suspect the heating system is not working effectively or efficiently.

danm

you can size requirments here

http://www.idhee.org.uk/calculator.html

was your bill actual or estimated??

I am kinda in the same situation. Moving from an average mid terrance with combi into large semi and my gas bill went from on average to a first actual reading bill that got me very exiting.

What gas tariff are you on. Given i just had just moved and had lots going on, British Gas had put my on the Standard Tariff without me questioning it which is about 40% more expenstive than the tariff i just switch onto. Try a comparison site. Also remember that you are probbably using 70% of your total heating bill between November and April. Should be much lower in summer.....

From hours of googling i came to the conclusion that big houses cost more and take longer to heat ....

What type of radiators do you have - If they are the 'standard' compact type are they single or double panels, double with convectors? YOu can use various site to size what radiators you need in terms of output....then try to visually compare the type....to see if you have the right size.

Seronera

Londonjoe wrote: »

Hi All,

I have a dilemma.

I've just moved into a fairly large semi detached house (2,000Sq ft).

They have a system boiler in the laundry room and an Aristan water tank in the pantry (connected immersion heater). The house has 7 radiators downstairs and 9 radiators upstairs with three toilets and two baths/showers.

At the moment we have a Glowworm 24 Hxi boiler (installed 2008) and with 1.5 hours in the morning and 3 hours use in the evening, received a bill for £200 for the gas for one month.

I suspect the heating system isn't working efficiently and so have had various engineers in to give me quotes. The advice received varies considerably from being told to fit a combi boiler for hot water on demand (the system I'm used to coming from a small terraced) to fitting a new system boiler (Valiant 937).

The advice on the size of the boiler has varied considerably and differs per engineer, with some saying the boiler is the right size to others stating it's too small.

It takes one hour to heat the house properly but the it never warms to above 17c.

Any advise on sizing would be appreciated. I suspect the heating system is not working effectively or efficiently.

There is definitely something wrong with the current system if you are using £200 in a month, but I reckon there might be something wrong with that figure as its impossible to use that much gas in 4.5 hours a day no matter what you do. Is that a bill or have you taken readings from your gas meter. Also its not an old system but a thoroughly modern system and easily repairable. I most certainly would not swap it for a combi which I view as an inferior arrangement. The Glow Worm 24Hxi is at least as efficient as any of the boilers you will be offered. It uses the same Heat Exchanger as the Vaillant being suggested as its replacement for heavens sake. So my suggestion to you is as follows.

If you cannot get a heating engineer who is prepared to talk in terms of a repair, then telephone Glow Worm customer services and get an engineer from their Group Service team to come out and service it and fix any faults on the boiler. They carry all the parts you might need to get it back to top condition. That will cost you just under £300 or so including parts and carry a years guarantee. You will then know the boiler is fine. Explain to them the problem with the 17C. It could be as simple as a failed thermistor on the flow pipe or a broken control knob into the printed circuit board. Then you need to check that your controls are working properly, that the heating comes on an off with the timer..ditto the hot water, and that the thermostats and diverter valves are effective

Is your water hard water as the Ariston cylinder may be scaled up, but if it is working properly it should go from cold to hot in no more than 30 minutes.

24Kw is certainly NOT too small. I heat a slightly smaller house with an 18kw boiler. The idiots who say it is too small don't know the difference between a system boiler and a combi if they say its too small. That tells you a lot about their level of expertise. In any event once the house gets hot these boilers modulate down to about 8 or 9 kW on the central heating. The Hot Water cylinder can only cope with about 4kw so 24 is massively enough (combis have bigger ratings to cope with the instant hot water demand. System boilers don't need to be half as powerful). Another thing that happens to Glow Worms is that if the pump is on too fast a setting it can upset the sensors and make the boiler stay too cool.

I suspect you are being conned into a new boiler quite frankly, and I'm a heating engineer. Remember that combis are no more efficient than a system boiler and cylinder (provided its well insulated) and that you have no hot water backup in the event of a boiler fault. You will find that the vast majority of heating engineers keep a hot water cylinder....if its good enough for them..etc etc.

C_Mababejive

Maybe you need to survey and address insulation/heat loss issues rather than pumping more heat in?

Londonjoe

Hi guys,

Thanks for the responses.

The bill is from actual readings, apparently i used 390 metric units during this period.

I've been monitoring the meter and it seems to burn through 2 metric units per hour when heating is put onto maximum.

I've had about 5 engineers in and all have very different opinions, which has left me very confused (scratching head). I definetely feel that heat loss needs addressing (we have a single glazing at the front of the house with a massive window in the hallway).

Also, the system may need flushing to improve the flow rate of water through it, though at a cost of £500 I'm still thinking about it before I commit.

I shall get some more engineers in to have a look.

psychic_teabag

Londonjoe wrote: »

It takes one hour to heat the house properly but the it never warms to above 17c.

I'm not a heating engineer, but from a simple physics standpoint, if it can't get above 17C, then either it decides to stop heating at that point (thermostats, etc), or that's the point where heat-in matches heat-lost.

Does the heating turn off when the house reaches 17, or is it still going full-pelt, with the radiators all hot ?

How quickly does the house cool down when you turn the heating off ? If it heats up in an hour, that sounds like there's plenty of power in the system. (My place is a lot slower to warm up...) But if it does cool down very quickly, heat-loss might be something to worry about.

I guess it could also be poor heat transfer from radiators to the room, but I wouldn't expect the temperature to plateau abruptly at 17 - it would either take a very long time to reach that temperature, or it should keep going up, though more slowly. And presumably the boiler would keep cycling since the water wasn't getting cooled in the pipework.

zaax

Insulation is the trick. 30cm in the loft and triple glazing in the living room; bath room & kitchen, double in the rest.

st999

What temperature is the water circulating round the radiators?

If it is too low the house will never heat up

Seronera

Londonjoe wrote: »

Hi guys,

Thanks for the responses.

The bill is from actual readings, apparently i used 390 metric units during this period.

I've been monitoring the meter and it seems to burn through 2 metric units per hour when heating is put onto maximum.

I've had about 5 engineers in and all have very different opinions, which has left me very confused (scratching head). I definetely feel that heat loss needs addressing (we have a single glazing at the front of the house with a massive window in the hallway).

Also, the system may need flushing to improve the flow rate of water through it, though at a cost of £500 I'm still thinking about it before I commit.

I shall get some more engineers in to have a look.

Many have mentioned insulation and of course that needs attending to. What vintage are the radiators? If they are not modern convector type (with fins) then a power flush may be poor value against swapping them for new ones. Convector radiators are cheaper than they have ever been and by shopping around you can replace a pretty high number for £500 (try screw fix to see competitive pricing). They are also a lot more efficient than older radiators and will be a much better match for the boiler, and maybe you can upsize some singles to doubles in critical locations.

I still think that is too much gas. Have you had the meter checked by the gas company. Some do over read. Put it another way....if its using the gas then its creating the heat as the boiler would go barmy if it couldn't get rid of its heat.....so what are you doing with the heat? It must be going somewhere...but where?

Do your radiators have Thermostatic Radiator Valves on? If not that is a majorly good way of distributing heat round a house where you want/need it. If you are heating rooms that don't need heating, or just need airing then you are bound to be wasting a lot of energy.

Roughly where are you in the country? I know some good engineers who like a challenge!!

Londonjoe

Of the radiators I reckon 6 are probably over 15 years old, the rest are about 6 years old. Apart from the 6 all the other radiators have thermostats on them.

You're right the heat must be going somewhere, maybe out of the flue....I hope not, ha ha ha.

Tonight, I've waited until now until switching the heating on, which I'll have on for an hour and will then switch off again. My last property was a terrace house so always cosy.

I live in North Harrow.

Johnandabby

2 m3/hr is 22 kW, which makes sense with your boiler's gas input.

If your boiler is working flat out during the limited hours that you are running it, then 390m2/month would also make sense - works out at an average of 6.5 hrs/day, do you run it for longer at the weekends?

You haven't said whether the property is new or old, cavity or solid walls etc. If it's not very well insulated, then heating demand could be 120 W/m2 or higher - at 2000 sqft this is a 24 kW heat demand to just maintain the internal temperature, and even more to heat up the house from cold.