Boiler sizing query?

[ericmark]

I have a 5 bed mid terraced house, rooms are not that big, during buiolding works in 2019 i installed new combi 30kw boiler without sizing n calcs, replaced some older rads and it worked out ok.

Working is not the same as working efficiently.

I know I don't need all rooms to be heated at the same time, many homes have two zones, mine has programmable TRV heads as well, so I can select when rooms are heated, the largest room has two double panel radiators, so can likely sink around 3 kW of heat, even with all mid-floor rooms being heated, only around 6 kW is required, so why did whoever designed the system think I needed a 20 kW boiler?

 

[PEDANTICVINDICTIVEMAN]

If radiators are getting nice and hot with 72deg going through them, and the rooms aren't hot enough, then rads undersized.

 

[Harry Bloomfield]

They had set the boiler to 90 degrees, outside temp was 10-11 degrees, house was 17.5 degrees at 5:15am, heating came on to rise to 22 degrees, by 6:50am it was only 20.2 degrees.

90 degrees, is ridiculous, and shouldn't be necessary, for either CH, or HW. Many/all modern boilers, have the ability to be set for different temperatures, dependent on whether they are satisfying CH or HW. For cylinder heating, to 65C, I have mine set to 75C.

Output temperature, is managed by my system, dependent on how cold outdoors, present, and desired temperature, but monitoring flow, it never goes higher than 60C, with a return a good 20C cooler. My system is 40+ years old, designed to cope with single glazing, drafty windows and doors, no cavity wall insulation - all since addressed, so the radiators are over sized, and normally run quite cool, and efficient.

3-bed semi, 9 rads, 18Kw boiler. We have the CH enabled round the clock, 18C, and 14C setback 10pm to 10am.

If all your radiators are hot, yet it still isn't coping with heating the place quickly, it suggests your radiators are too small, or the heat-loss too high.

 

[JohnD]

Detached
5 bed
1805 square feet (c. 168m2)
3 floors

It might be enough if it is a modern house with cavity wall insulation, thick loft insulation, good draught proofing.

Is it?

I used to have a house of comparable size, but Edwardian, with solid walls, and a 30kW boiler was insufficient on a frosty night.
It was EPC rating E.

Is yout boiler constantly running at full power, or does it modulate down after the radiators are hot?

Have you got an EPC for the house?

Find an energy certificate

Find a property's energy certificate including an energy performance certificate (EPC), display energy certificate (DEC) or air conditioning inspection certificate.

www.gov.uk

 

[ericmark]

I used to have a house of comparable size, but Edwardian, with solid walls, and a 30kW boiler was insufficient on a frosty night.

This is what I was finding, however, I realised the boiler was turning off prematurely. Even harder to find if boiler turning down rather than off. My house is D and D, 150 m² and 44 m² for some reason they have issued two certificates one for main house other for flat under main house, 1 point on the energy performance certificate equals on average a saving of £38.50.

For my house

An average household would need to spend £442 per year on heating, hot water and lighting in this property. These costs usually make up the majority of your energy bills.

who do they think they are kidding, oil alone cost that. OK now solar panels, extra loft insulation, battery, loft floored, better double glazing fitted, so we may just sneak into the £442 now, as electric bill is nearly zero.

I would guess we use around 400 gallons of heating oil a year, I think we have a 600 gallon tank, 1 gallon around 50 kWh, so using around, 20,000 kWh per year, since no heating needed in summer, I will guess around 500 kWh per week, so average of 3 kW per hour, which seems to make sense, as boiler does not run that often, which is a problem as it causes a huge hysteresis between each time it fires.

Adding extra thermostats stops the slow cooling of the hall cause the living room from getting cold.

168 m² is much smaller than my 194 m² but the boiler is smaller, however it still should be ample.