2 Oil Boiler Q's: Summer DHW & Range Rating

[Missing Lincs]

Hi Chaps,

I have a couple of questions regarding our oil boiler installation - a Grant Vortex Pro 15/26, serving an unvented cylinder.

1) I've read on another (non-plumbing!) forum that it's inefficient to use the boiler solely for hot water heating during the summer months, when the CH is off. The suggestion was to use the immersion heater only. No reason was given, but I guess the reasoning is that you're not heating up the system water in boiler and pipery - just 'injecting' heat directly into the cylinder. So although the kWh 'unit cost' of leccy is higher than oil, it still works out cheaper. Is this true, or a load of old cobblers?

There's only the two of us, so our water needs are quite low. Currently, I'd say the boiler does one half-hour burn morning and evening to satisfy our needs. The boiler has been 'range rated' to 15kW, so it does this without short-cycling. Which brings us to:

2) When we had the system installed in 2015, the boiler was range rated right down to 15kW. This was enough at the time, but we had plans to extend the house a little later on. Unfortunately, employment uncertainty has put those plans on hold, so my other question is whether any long-term problems could occur running the boiler at its lowest 'setting' for two or three years - or is it fine to run it like that indefinitely?

This is the first oil system we've had, so it's all a bit new!

Cheers

 

[oilhead]

1. There is a lot to be said for keeping the boiler 'exercised' during the summer months. It will keep things turning that may otherwise get stiff. It will keep the fuel fresh in the supply and stop sediment settling. Also, your immersion heater will probably only heat up the top 1/3rd of your cylinder, and although you may have a low water usage, You may find when you run a bath that you've used up all the available supply, so have to switch on your immersion again. Oil, particularly in the summer, is significantly cheaper than electricity.
2.Your boiler is designed to run at the rate you have it set, so no problem there.

 

[muggles]

1. Cobblers. It'll cost you three to four times more to use the immersion heater

2. Nothing wrong with that. Remember to get it serviced annually

 

[Missing Lincs]

Many thanks for the replies, guys.

Yes, the hot water 'advice' was on a motoring forum - and did sound a bit 'sus'

I'm actually quite warming(!) to the oil boiler - it's reassuringly low-tech which suits my somewhat Luddite tendencies

 

[Agile]

You are using 30 kWh a day using your oil boiler.

Electricity to heat the cylinder will probably be a lot less that that. Perhaps just 5-10 kWh.

So potentially a bit of a saving.

But even if you did then it is still useful to exercise the boiler regularly.

Perhaps a partial solution would be to use oil in the morning and to top up with electricity in the evening.

Or the other way so that the oil boiler contribution is the higher of the two heating periods.

Is your cylinder well insulated? Sounds like a considerable heat loss each day.

Tony

 

[Missing Lincs]

Hi Tony,

Isn't it more like 15kWh? Plus, I may have been a bit 'over-generous', and the half-hour is a maximum (after a lot of hot water usage).

The cylinder's nominal heat loss is 1.45kWh per day.

 

[Agile]

Sorry, you are quite right based on your figures it would only be 15 kWh per day from the oil.

Your half hour seemed a bit short and I mentally increased that.

But with a well insulated cylinder it is going to be alright.

But with the well insulated cylinder the electric heating would be less wasted.

Regardless I would use the oil boiler to heat it fully in the morning for up to an hour and give an electric top up in the evening.

Remember every time you use the boiler it also to be heated up from cold wasting energy.

 

[Missing Lincs]

Remember every time you use the boiler it also to be heated up from cold wasting energy.

Yes, that's what I was thinking might be behind the logic. It's a hefty external boiler with a water capacity of 19 litres, so it takes a good few minutes to get the flow temperature high enough to have any effect. Heat must also be wasted during the boiler cool-down....

Thanks again for the helpful replies,
David

 

[Agile]

That's why a timed hour in the morning will fully heat the tank and the electricity can do a top up in the evening.

The boiler will be turned off by the cylinder stat as soon as it it up to temperature.

You might well be using up to 5 kWh just heating up the boiler from cold and that has to be remembered when thinking that oil is cheaper than electricity.

Its also good to have a full run up every day during the summer to keep it in good running order.