Heat Loss Calc For Heat Only Boiler

[JackK]

I have a heat only boiler

I had a heating engineer provide a heat loss calc

His calculation was

2.5Kw per radiator ​

3Kw for the hot water cylinder ​

As I have 17 radiators this comes back at 35Kw and he suggested a 35 or 42 Kw

Judging by posts on this site this seems far too high

Is 2.5Kw per radiator about right? If so then this is a correct calculation

Seems high to me for a 4 bed detached house

 

[oldbuffer]

1. "2.5 kW per radiator" is not a heat loss calculation, its a rule of thumb.
2. Heat loss depends on all sorts of things, primarily the rate at which windows and external doors / wall lose heat and the size of the rooms.
3. If the house is sufficiently warm, and warms up quickly enough, then:
3.1 For each room, measure the existing radiator(s), determine its type (single, double, with fins, without fins).
3.2 Look up three makes of radiator for the same approximate size and type, and take an average of the output.
3.3 Sum the results of 3.2 above.
3.4 That gives you the heating load. I would add 10% as a "just in case" for very bad weather.
4. Allowing 3 kW for the hot water is a fair approximation unless you are going for a "fast recovery" cylinder. If you are, use the manufacturer's kW figure.

 

[fixitflav]

Allowing 3 kW for the hot water is a fair approximation unless you are going for a "fast recovery" cylinder.

I would say 3 kW is plenty for the HW cylinder, even if it is a fast recovery type. In that case the instantaneous demand might be higher, but it will only last a short time.

 

[Rodders53]

Ideally nowadays one wants to go Hot Water Priority which, rather like a combi boiler when filling a bath, will turn off the CH flow for the shortish time (20-30 mins typically) taken to reheat the HW cylinder. {and with the modern type boiler that can provide cylinder reheat flow temp much higher than CH flow temp, so as to ensure CH is fully condensing, as well as reducing the HW reheat time}.

Heat loss calcs into radiators therefore need to be done at lower design flow temps... in line with current 'best practice' (if not now included within the building regs).

Rules of thumb no longer cut it.

 

[Mister Banks]

I have a heat only boiler

I had a heating engineer provide a heat loss calc

His calculation was

2.5Kw per radiator ​

3Kw for the hot water cylinder ​

As I have 17 radiators this comes back at 35Kw and he suggested a 35 or 42 Kw

Judging by posts on this site this seems far too high

Is 2.5Kw per radiator about right? If so then this is a correct calculation

Seems high to me for a 4 bed detached house

2.5kw per radiator is wrong. A heat loss calculation is done by room not radiator.

 

[Notch7]

I have a heat only boiler

I had a heating engineer provide a heat loss calc

His calculation was

2.5Kw per radiator ​

3Kw for the hot water cylinder ​

As I have 17 radiators this comes back at 35Kw and he suggested a 35 or 42 Kw

Judging by posts on this site this seems far too high

Is 2.5Kw per radiator about right? If so then this is a correct calculation

Seems high to me for a 4 bed detached house

If you have a boiler fitted that is too big, it probably wont be able to modulate down enough to cater for the lowest demands

As others have said, ask about hot water priority -makes a big difference on efficiency

 

[RandomGrinch]

I have a heat only boiler

What model/power is your existing boiler, and have you had any issues with it?

 

[DP]

I have a heat only boiler

I had a heating engineer provide a heat loss calc

His calculation was

2.5Kw per radiator ​

3Kw for the hot water cylinder ​

As I have 17 radiators this comes back at 35Kw and he suggested a 35 or 42 Kw

Judging by posts on this site this seems far too high

Is 2.5Kw per radiator about right? If so then this is a correct calculation

Seems high to me for a 4 bed detached house

Jack, correct way to do your heat loss is to find a website that shows your radiators and then see what each radiator you have outputs

Other is to do long hand calculations of each room element. Sum of these losses plus 10% gives you radiator sizes. Rule of thumb often used is 1.5kW per radiator. Say 18 radiators, will need a boiler rated at 27kW. 28kW is the standard.

One point to consider about cylinder is the fact that coil is rated at 24 kW which heats the water in the cylinder in 15- 18 minutes to about 75% capacity. There is an immersion heater fitted rated at 3kW. You can allow 3 kW off the boiler but will need to wait ages for the water to heat up unless you run the hot water programme when rads are off

 

[cdbe]

I have a 15kw, more than enough for a large 1930's 4 bed semi. If you do end up a bit short just time the HW outside the heating times. I think my cylinder is rated at just under 16kw so a good match.

 

[JonathanM]

I've had heating engineers quote me anything from 18KW to 30KW.

I'm just a DIYer. So, this might be nonsense! But it seems logical.

If you can find out how much gas you currently use on a very cold day to keep the house warm. For example, my bill shows gas use both daily and every half hour. So I can find a couple of days last December when it was -3C and see how much gas I needed.

And if you have a rough idea of what your current boiler efficiency is. Then you should be able to work out an estimate of what your house actually needs. It won't be exact, but it might give you a very rough idea of what you need. Mine came out about 9KW.

 

[DP]

I've had heating engineers quote me anything from 18KW to 30KW.

I'm just a DIYer. So, this might be nonsense! But it seems logical.

If you can find out how much gas you currently use on a very cold day to keep the house warm. For example, my bill shows gas use both daily and every half hour. So I can find a couple of days last December when it was -3C and see how much gas I needed.

And if you have a rough idea of what your current boiler efficiency is. Then you should be able to work out an estimate of what your house actually needs. It won't be exact, but it might give you a very rough idea of what you need. Mine came out about 9KW.

Jack, if your current boiler can maintain temperature, your proposed boiler will have output same as current boiler

 

[vulcancontinental]

Get another heating engineer or do it yourself if you have time and a tenner. Use Heat-Engineer software. You'll spend a day but you'll have an accurate heat loss calculation.