Gas combi boiler

Albermarle

moneytalks said:

Sorry to all of I’m asking stupid questions. I had oil fired heating for 30 years. No TRV just on or off.
The age old question, is it cheaper to run heating on low or turn on when you are cold and turn off when warm?

It depends on the property.
With a  small well insulated flat with others above, below and on both sides, then the heat loss is low, so leaving the heating on low all the time makes sense.
However with a poorly insulated large old house, which loses heat quickly, it is better to only heat it when needed.

ThisIsWeird

Yessish.
As a simple rule, only heat your home when and where it is required. The higher the inside temp, the greater the loss of heat to the outside.
That's the MSE facts of the matter. So, only heat when required.
However, for some older or poorly insulated homes, there is a theory that allowing the fabric to become too cold can cause the walls to become 'damp', and so conduct heat away more than usual. So, possibly, for such properties, having a constant 'minimum' (say 12 or 14 or even slightly more) background heat level might work better overall.
Ditto if you find that turning on the heating just when you want it simply doesn't work for you, as your house takes hours to get up to a comfy temp. Again, you may consider a min background temp is maintained, with it being boosted as and when required.
So, do what you need to be reasonably comfy in your own home, but bear in mind that, as a rule, the longer you heat your home - min or no - the greater the energy loss. 
For rooms that are not being used - like 2 bedrooms in our house as kids are away - the heating is fully off in there, and the windows cracked open to 'vent'. Bludy chilly in there, but absolutely zero damp. Not a trace of mould or condie.

FreeBear

moneytalks said:

FreeBear said:

moneytalks said:

FreeBear said:

Even with OpenTherm connected, the flow temperature could be swinging up & down due to the boiler short cycling. Many Baxi boilers won't modulate down to under 6kW and with 4 TRVs set to 1-2 and the rest on 3, quite likely there is insufficient heat demand.

My boiler can modulate down to ~3.2kW, and just one TRV activating can be enough for the boiler to start short cycling.

Should I have all the TRV at a higher setting?

Up to you.

I have all my TRVs set to max as i don't want the boiler short cycling. It doesn't appear to have increased my gas consumption.

Do your rads ever cool down when you have them to max or are they always very hot?

The radiators only heat up when the boiler is running. And even then, never too hot to put a hand on - At most, 60°C, but more often than not, around 50°C.

If your radiators are getting to 70°C or more, there is a very real risk of burns, particularly with the young and elderly. On top of that, corrosion inside the radiator is accelerated, so more sludge being generated to clog up your boiler.

As for which is better, heating on all day, or just on a couple of times a day - It depends. Even although my house is close to 100 years old, I've improved insulation levels where possible and don't lose a great deal of heat. I had been setting the heating to come on first thing in the morning, and remain on for most of the day. Once up to temperature, the boiler would kick in for ~30mins every hour or two just to top up the temperature. For the last couple of weeks, I've been running the system to turn on first thing, off once up to temperature, and then repeat every 3 hours or so. The temperature swings a bit more, and the boiler might run for 30-45mins at a time. Gas consumption has remained about the same, but gained a point or two on efficiency. But it is difficult to give a definitive answer as there are too many variables outside my control. Ambient temperature outside, levels of sunshine (I have a lot of solar gain when the sun shines), and wind.

moneytalks

Rodders53 said:

Yes. Normal.

Google < thermostat hysterisis >

NB your temp is possibly a tad on the high side and you may be more energy efficient (fully condensing) if you can go a bit lower.

Forgot to add the boiler is 36Kw, so is it ok to reduce the temp to 55c?

FreeBear

The rating of the boiler doesn't really matter. As long as the house heats up at a rate that you are happy with, turning the flow temperature down to 55°C will improve efficiency.

I'll run my boiler at that sort of temperature (and lower). But I also have oversized radiators to achieve a 1°C per hour increase in room temperatures. It works for me.

moneytalks

FreeBear said:

The rating of the boiler doesn't really matter. As long as the house heats up at a rate that you are happy with, turning the flow temperature down to 55°C will improve efficiency.

I'll run my boiler at that sort of temperature (and lower). But I also have oversized radiators to achieve a 1°C per hour increase in room temperatures. It works for me.

I put the gas on for an hour or two in the morning. If I reduce the flow rate, am I right in thinking I’ll need to run for longer  to heat the house?
I had run at 65c for an hour. I think another problem is I have a credit meter for my gas, and the temptation to see how much gas I’m using over a day😁

Albermarle

moneytalks said:

FreeBear said:

The rating of the boiler doesn't really matter. As long as the house heats up at a rate that you are happy with, turning the flow temperature down to 55°C will improve efficiency.

I'll run my boiler at that sort of temperature (and lower). But I also have oversized radiators to achieve a 1°C per hour increase in room temperatures. It works for me.

I put the gas on for an hour or two in the morning. If I reduce the flow rate, am I right in thinking I’ll need to run for longer  to heat the house?
I had run at 65c for an hour. I think another problem is I have a credit meter for my gas, and the temptation to see how much gas I’m using over a day😁

Yes if you reduce the flow temperature, the radiators will not get as hot, so the house will take longer to heat up.
It will be more noticeable when the weather is very cold.
The main point is that the lower the temperature when the water has been around the system and back to the boiler, the more efficiently the boiler works, as it aids the condensing action of the boiler, which saves gas.
So even if you have to leave the gas on longer to heat the house, overall you should use less gas with a lower flow temperature, as the boiler is running more efficiently.

In reality running at 65 is not really too high. Although the boiler will be more efficient at 60 or even 55, the gains will not be huge.
If you go above 65 to say 70 or even higher, then the boiler will become significantly more inefficient. Also the radiators will become very hot to touch. 
I run at 65 in the 'proper Winter' but turn it down to 60/58 in November, March etc when the weather is just cool rather than cold. 

FreeBear

Albermarle said:

moneytalks said:

FreeBear said:

The rating of the boiler doesn't really matter. As long as the house heats up at a rate that you are happy with, turning the flow temperature down to 55°C will improve efficiency.

I'll run my boiler at that sort of temperature (and lower). But I also have oversized radiators to achieve a 1°C per hour increase in room temperatures. It works for me.

I put the gas on for an hour or two in the morning. If I reduce the flow rate, am I right in thinking I’ll need to run for longer  to heat the house?
I had run at 65c for an hour. I think another problem is I have a credit meter for my gas, and the temptation to see how much gas I’m using over a day😁

Yes if you reduce the flow temperature, the radiators will not get as hot, so the house will take longer to heat up.
It will be more noticeable when the weather is very cold.
The main point is that the lower the temperature when the water has been around the system and back to the boiler, the more efficiently the boiler works, as it aids the condensing action of the boiler, which saves gas.
So even if you have to leave the gas on longer to heat the house, overall you should use less gas with a lower flow temperature, as the boiler is running more efficiently.

In reality running at 65 is not really too high. Although the boiler will be more efficient at 60 or even 55, the gains will not be huge.
If you go above 65 to say 70 or even higher, then the boiler will become significantly more inefficient. Also the radiators will become very hot to touch. 
I run at 65 in the 'proper Winter' but turn it down to 60/58 in November, March etc when the weather is just cool rather than cold. 

Heat Geek have a graph showing how efficiency improves as the return temperature drops. But it isn't a particularly brilliant graph. The graph below is a little better... Boilers are generally more efficient when run at partial load (manufacturers will often quote efficiency at 30% and 100%).

Nearly all boilers fitted are way oversized for the property. 30kW is not that uncommon, and heating often only needs 6-8kW. So you'll probably be running at 25% of capacity. With that in mind, if we use the graph below, at a 70°C flow and a 50°C return temperature, you should be getting around 90% efficiency. Drop the flow to 60°C, return temperature should be around 40°C for an efficiency of ~94%. Going down a flow of 50°C (return will be ~35°C) might get you up to 95-96%.

The one thing these graphs do not show, is how inefficient a boiler is when it fires up - You could be as low as 75% for the first few minutes. One reason you should try and limit short cycling (some boilers have a setting limiting the number of burner starts each hour).

Grandad2b

I now have a draft comment I can't delete...

I think.

Let's see if posting this does the trick

FreeBear

moneytalks said:

FreeBear said:

The rating of the boiler doesn't really matter. As long as the house heats up at a rate that you are happy with, turning the flow temperature down to 55°C will improve efficiency.

I'll run my boiler at that sort of temperature (and lower). But I also have oversized radiators to achieve a 1°C per hour increase in room temperatures. It works for me.

I put the gas on for an hour or two in the morning. If I reduce the flow rate, am I right in thinking I’ll need to run for longer  to heat the house?

Yes, but it is a balancing act between how fast the house heats up, boiler efficiency, and gas consumption.

During December, I had dropped flow temperatures right down. Boiler would be running for 2-3 hours just to raise the temperature by 1°C. I might have been getting 96-98% efficiency. Turn the flow temperature, efficiency drops to ~92%, but heating is only running for 1-2 hours for a similar temperature increase.

Unfortunately, there is one factor beyond the control of us mere mortals that affect the results - Outdoor temperature !

So run your heating system with a flow/return temperature that heats your house up at a reasonable rate. The amount you save by going from 65°C to 60°C is only going to be pennies a day. But heating costs is highly dependent on weather (my heating bill can drop 50% when the sun shines).