Old boiler replacement

[amcluesent]

The salesman's quoted efficiency of condensing boilers of 95%+ vs open-flue boilers at 60% is based on ideal circumstances. The most relevant being that the condensing boiler can be run with a flow temp of 55°C which usually requires very large rads or ideally underfloor heating. Also that the combi is running with weather compensation, has a high modulation ration and the CH water is crystal clear.

 

[ericmark]

I was surprised on moving here to a larger house that my heating bill went down. OK moved from gas to oil, but more likely down to control.

But loses from pipes I had expected to be high, at least in the summer, I have no tank thermostat, my only control for DHW is time. It runs for ½ hour three times a week in summer, in winter switched off, in real terms 20 minutes not ½ hour as boiler cuts out before ½ hour has lapsed.

The heating does not work as it should, the wall thermostat is in the hall, which cools too slow. And the TRV's are not linked.

But although clearly we need to lag pipes where the heat is a loss to the home, my airing cupboard is central, so loses only matter in the summer, un-lagged central heating pipes still heat the floor so the house.

A modulating gas boiler which can extract the latent heat will only be an advantage if it is allowed to work in an economic way. Every time it is switched off and back on, it will restart in the main flat out, and only as the warm water returns and it starts to modulate will the efficiency improve over the older boiler, which means allowing the TRV to do its job, and the wall on/off thermostat should likely only switch half a dozen times a day when there is a programmed temperature change.

There are wall thermostats which turn the boiler up/down rather than on/off, these are claimed to save more energy, but not sure they work in real terms.

If the boiler turns all the steam in the flue gases to water within the boiler, then we will not see plumes of steam from the flue, but we do, so they can't be set up correctly.

My boiler does not gain the latent heat, it fires up and runs for at least 20 minutes, takes that long for the radiators to warm up, and each time it starts and stops some heat is lost, so want a reasonably long burn, there are three floors to this house, 5 bedrooms, 2 kitchens, two living rooms, two bathrooms, plus shower and toilet room, dinning room and a utility room unheated. Only one kitchen, the living room and two bedrooms really used, a motorised valve turns off the lower kitchen, bedroom, living room and bathroom unless we have visitors, and the dinning room, and two upper bedrooms are only heated we required. The main kitchen only heated until 6 pm, so although the boiler is only 18 kW it is ample, it states 20 kW in and 18 kW out, so that's 90% efficient.

 

[JonathanM]

Control of most central heating is done with the TRV's they come in three basic flavours, mechanical, local programmable, and linked programmable. The programmable heads can be direct only or use bluetooth the latter is used when two radiators in the same room, but clearly they will not heat up the room unless the boiler is running, so the terrier i30 and the eqiva eQ-3 can be used to turn off rooms when not in use, but need some careful setting up, I turn the main thermostat down ½ a degree for an hour before the TRV is programmed to heat the room then back up at same time as TRV is set to open to ensure boiler runs.

The Drayton Wiser or EvoHome do not need you to carefully set the schedule as linked, so easier to set up, but cost more.

I made a mistake, I got Nest which I then found out does not link to TRV's, I was miss informed, I thought it would, but the two programmable heads I have, the cheaper actually works better, main good point is I can on the TRV head simply press a button or turn dial, the other one need to use my PC.

If I was starting again I would have two rooms with linked TRV heads and rest the eQ-3 which only cost me £15 each in 2019 for the bluetooth versions.

Thanks, I hadn't really understood how programmable TRVs worked before. Mine are all 30 year old mechanical, but there's been a couple of new heads over the years.

I don't really know anything about oil boilers, either. You said that yours doesn't gain the latent heat, so is your boiler non-condensing?

 

[Ltnman]

It won't save anything because of it being a combi. A new heat-only or system boiler would be as efficient as a combi, and better suited to your requirements.

Except you have no idea what their family requirements are. Heat only boilers can’t be turned down below around 60c due to the possibility of legionaries disease. They will provide a hot tank of water whether it is needed or not and cannot offer an independent temperature to the central heating. The down side of a combi is the waste of water waiting for hot water to appear at the tap and the waste of gas getting that water to the tap. Tanks are more suited to large families requiring two showers or baths at the same time. I live in a home of 4 adults but we shower one at a time despite having 2 showers and a bath.

I'd estimate around 40-45p in every pound will go up the flue with your current boiler depending on controls and 15-20p in the pound with a new boiler. Guesses of course but closer than £1000/year saving.

As a combi is 88% efficient if condensing takes place and up to 96% efficient if lower return temperatures are achieved then a combi is putting between 4% and 12% of its energy out of the flue.

 

[JonathanM]

As a combi is 88% efficient if condensing takes place and up to 96% efficient if lower return temperatures are achieved then a combi is putting between 4% and 12% of its energy out of the flue.

I think I saw in the manual that your boiler can display the efficiency, but not sure what that option actually does.

I live in a home of 4 adults but we shower one at a time despite having 2 showers and a bath.

Saw earlier that you can all shower for 3KWh which sounds very efficient. A full tank here costs just over 10kWh to heat!

 

[Johntheo5]

That's pretty efficient shower usage as it works out at ~ 2 min shower/person at 10LPM.

 

[Ltnman]

I have an aeration shower head that outputs 5 litres a minute of hot water according to the boiler with a smidgen of cold water added. We do the dishes at 42C but that is too hot for the shower. Got to say no one is complaining about the shower flow that has the added bubbles to mask the actual output.

I think I saw in the manual that your boiler can display the efficiency, but not sure what that option actually does.

Boiler shows being 100% efficient when clearly it is not.

 

[JonathanM]

I have an aeration shower head that outputs 5 litres a minute of hot water according to the boiler with a smidgen of cold water added. We do the dishes at 42C but that is too hot for the shower. Got to say no one is complaining about the shower flow that has the added bubbles to mask the actual output.

Do you limit how much you open the shower valve? Or does it somehow limit the flow automatically?

 

[Johntheo5]

Mira make a (electric) shower that aerates the water as well.

Actually, I only shower for 2 mins or less (twice daily) but sadly, that wasn't the case years & years ago with teenage children.

 

[ericmark]

Heat only boilers can’t be turned down below around 60c due to the possibility of legionaries disease.

Mine goes down to 55°C at boiler, likely lower at the tank, there is not tank thermostat as early C Plan I control amount of hot water with just time.

They will provide a hot tank of water whether it is needed or not and cannot offer an independent temperature to the central heating.

When it uses a motorised valve it can give a temperature less than the central heating.

The down side of a combi is the waste of water waiting for hot water to appear at the tap and the waste of gas getting that water to the tap.

It does depend on the boiler and location of the boiler, Mother had a Worcester Bosch boiler, it had an Eco button, with Eco on the shower would start cold and warm up as hot water reached it, but to get hot water at sink tap, it had to be full on, but switch off Eco and you could get hot water faster at the sink taps, and with a low flow rate, but the shower would start cold, go hot, then cold again, and then hot second time and stay hot.

There was clearly a small reservoir in the boiler, and with eco off it was used, but with eco on it was by-passed, the oil combi boiler always have a small reservoir as they can not modulate to same extent to gas, so unless using in eco mode you still have a tank of hot water.

Before having a combi I had two boilers, one for domestic hot water and one for central heating, combining them resulted in a small reservoir, and inability to have DHW when we had no electric, but today pilot flames are rare.

But even DIY unlikely to be able to swap a boiler for under £1000, likely cost three times that, and it takes a long time to get that back with higher efficiency, very likely 10 years, so question is in 10 years time what will have changed?

We have multi fuels which can be used, wood pellets, oil, LPG, town gas, solar, electric, and we have no idea how the price will change for each fuel. My brother-in-laws old house could use solar, wood burning stove, electric or LPG. It had a reinforced floor, and two massive water tanks, all heat was put into the water, and drawn out of the water to use, seemed an ideal system, but installation cost over £12k.

We look at heat pumps, seem a good idea, they can heat or cool, although it seems most being fitted can only heat, I can see the problem, heat raises, so a radiator low down will heat house, where a radiator high up will cool a house, so to combine you need fan assistance, now the fan assisted radiator uses fan speed to regulate output, the Myson iVector has a 5 speed fan, but it does not restrict the water flow, so really need to be in series not parallel, this means it all needs re-piping.

So central heating uses near enough engineering in the main, it just costs too much to have a system which will really control home temperature, there is no perfect system. It would cost too much, and although oil boilers last for years, mine is 18 years oil, and is likely to be 40 years old before it needs changing, gas don't seem to last as well, and at work the boiler was built 1902, and 1900, they really boil the water, and both have about 8 years to run on their ticket. there are some new boilers around

this one at Corris built 2005, this one

not in steam yet as far as I know, also Corris built this year. But boilers should last for at least 100 years if looked after.