# Efficient heating of DHW cylinder with Vaillant ecoTEC

It's also worth bearing in mind that each tank reheat takes 4kWh that could cost you as little as 20p depending on your gas cost. If you save 10% then that's 4p per day for two reheats. At the end of the year you can all go out and have a MacDonalds to celebrate, but that's about all.

Okay, a quick look at the gas prices in my spreadsheet reveals if I lowered by usage back to the old boiler's levels (-20%), I would save £16 over the summer.... so could perhaps even afford a McFlurry as well for the kids!!

Seriously, I guess I was looking too much at percentages and forgetting the underlying value!

Still don't understand why this is using 20% more fuel than my old boiler but think I'll use my time more productively and just tweak for comfort levels rather than chasing a McDonalds meal!

Thanks everyone for their advice above, I've now learn't a little bit more!! -8)

See what I have added to my last posting !

I do have to admit I like to chase the last % of efficiency at home.

But I dont like McDonalds ( apart from their hot apple pies, now £1.29 for two).

But he could have TWO of the McDonalds if he insulates his pipes!

I would also tentatively suggest you try the effect of increasing the delta on the flow valve. Thats assuming you have an auto bypass valve.

Yes, I do.

Regarding the boiler power, I now think that about 6-9 kW may be more appropriate for your needs. The purpose is to have it low enough to prevent/reduce the boiler cycling off.

I'm now getting 12C delta (with cylinder valve half closed) on d.40/41 until the flow temperature reaches 70C, the boiler then modulates down and so does the delta. Using the formula Flow (l/min) = Power (kW) ÷ 4.1 (kJ/l/K) * 60 (s/min) ÷ &#916;T (K) gives me a flow rate of 12.19 l/min. If I then modify the formula &#916;T (K) = power (kW) ÷ flow (l/min) ÷ 4.1 (kJ/l/K) × 60 (s/min) I can work out that the boiler is modulating down to approx 6-7kW.

You can calculate the power adsorption by having the boiler stably heating the water and measuring the gas rate at the meter ( see FAQ )

I've just checked the FAQ and couldn't find it? Could you provide a link?

#### DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Replies
4
Views
416
Replies
2
Views
7K
Replies
0
Views
916
Replies
7
Views
18K
Replies
4
Views
518