Slightly off topic heating-related/green energy question

FB. · Sep 1, 2012

Hi guys.

This is quite a long post, and perhaps a bit off-topic, but I suspect that this section of the forum is about the best place to start asking......

As you'll know, I am enthusiastic about "green" and "eco-friendly" solutions. I recycle, I grow my own fruit and veg, I have solar PV and I try hard not to waste anything (but I'm not a hoarder!).

With the cooler temperatures as we slide towards the shorter days, thought has turned to the central heating system.
Currently my four-bed detatched house is heated by the following 20-odd-year-old gas-fired boiler:

Manufacturer: Potterton
Model: Netaheat Profile 60e
Estimated date of manufacture: 1988-1991

I think that when the house was built, it was fitted with what was "passable" as qualifying for central heating, but at the lowest possible cost to the housbuilders, so not really up to the job, especially as it aged.
I reckon that the boiler would be more suited to a 3-bed det, rather than four-bed det. I would be interested to hear others views on this.

It's old, tatty, noisy and struggles with the burden of heating the house when the temperature is persistently below about five degrees; it has to run non-stop when it's really cold in December to February and has occasionally shut itself down due to it overheating while trying to cope with the load on it. I bleed the radiators every autumn to improve efficiency.
As for managing to heat the hot water as well as the house in winter, you must be joking! Fortunately there is an electric immersion heater to pick up the slack.

However, we occasionally have to resort to backup electrical heaters to bring the temperature up quickly enough (the temperature tends to only rise about 1-2'C an hour); the kitchen/understairs cupboard is the only gas connection, so we would have to pay out £££'s to install a gas heater in the lounge, and there would be fitting problems due to an open fireplace which we would not want to lose as it's nice to have an open fire at Christmas (we block the draught when the fireplace is not in use).

We have our doubts about how much longer the boiler will continue to run without becoming a lost cause or leaving us shivering in the middle of winter, and we also wonder how inefficient it might be by modern standards.

So, as a heating system numpty, and having laid out the current situation, I would like to ask:

1.
Is the boiler really inefficient by modern standards?

2.
How long do boilers usually last? This one seems like your old granddad who manages to keep going despite poor health, excessive drinking and smoking.

- and here's the question relevant to the topic being posted in this section:

3.
Would a "renewable" technology, such as heat pump, be worth considering - especially given that during the daytime we often tend to have an excess of solar electricity which just goes into the grid (we manage to use about half of what's generated from a 3.7kW array).

Any thoughts, ideas or even comments would be appreciated - and thanks for bearing with me to get to the end of all the waffle above!

Cheers,
F

Gavin A · Sep 1, 2012

1 - it's peak efficiency is 77% vs around 90% for a modern condensing boiler. I also don't think it's capable of modulating efficiently, so will be less efficient at lower loads where it will probably just cycle more (which results in all the heat in the pipework being lost, being reheated, being lost etc.)

2 - If properly maintained they can last for decades. I think our old one was 40 years old before we eventually got it replaced.

3 - Possibly, but you're unlikely to get much excess PV generation at the time of year when the bulk of your heat demand will be. I'm sceptical of the benefits of ASHP in areas on the mains gas grid vs a condensing gas boiler, as ASHP efficiency decreases with outside air temperatures vs demand increasing with the decrease in outside air temps, so the bulk of your consumption will be at times when the units are at their lowest efficiency levels. Their efficiency also drops if you're needing to use them as direct boiler replacements to use existing radiators, so are best installed in highly insulated building with wet underfloor heating, or oversized radiators. Outside of these situations, I just don't see that they'll achieve energy, carbon or cost savings vs a modulating condensing gas boiler.

sambotc · Sep 1, 2012

Hi FB,

The boiler and associated pipework is probably feeling the effects of age, reduced efficiency/heat exchange and increased resistance. Netaheats only had 2 stage modulation high and low.

hard to tell if the boiler is undersized for your house without measurements, construction materials etc, but I suspect probably not. The radiators may be undersized, or the pump getting lazy if your going into overheat but again impossible to tell really without a site visit.

An ASHP replacing a gas boiler will not be eligible for RHI so consider that. You'll be better off with a new boiler and controls, and maybe some maintenance work on the system depending on condition. I would consider a new heat only condensing boiler to replace the netaheat, keep/replace/upgrade the cylinder and consider an immersun unit.

Look into weather compensation units for the new boiler, most manufacturers are doing them now, some better than others. Basically they reduce the flow temperature of the boiler as the outside temperature increases. They take a bit of getting used to as your heating may have to come on earlier, but keep the boiler in maximum efficiency for as long as possible.

Upgrade to thermostatic radiator valves and a room thermostat if you don't already have them.

Upgrade insulation if not already done, it's more effective to reduce your consumption than change the technology.

As for how long they last, your is at the age of needing replacement to be fair.

SRE · Sep 2, 2012

sambotc said:
As for how long they last, your is at the age of needing replacement to be fair.

and better to change it now when you have time to weigh up the pro's and cons and get a decent plumber than have an emergency boiler replacement when you're grateful to get whatever you can to keep you warm.

AS others have said - no to ashp if you've got natural gas even the best ashp's struggle to heat when the temperature drops below zero and when they do "cope" it's using peak rate electricity. Ashp's have their place in very well insulated homes, particularly if they are installed with underfloor heating, rather than retrofitted to existing systems. Natural gas is going to be around for a while yet and is going to be cheaper than electricity.

Thermodynamics look like they may be something to watch for the future so bear that in mind when you're new system is being designed. They may be expensive now but could offer cost effective potential before too long.

I've been talking to a few heating engineers in the last couple of months and they are all saying the same thing - most people have really poor heating controls and this is one of the most cost effective methods for getting your fuel bills down (after insulation of course!). Some of the energy management systems are looking quite interesting.

FB. · Sep 2, 2012

sambotc said:
Hi FB,

The boiler and associated pipework is probably feeling the effects of age, reduced efficiency/heat exchange and increased resistance. Netaheats only had 2 stage modulation high and low.

Hi sambotc

Thanks for the reply. The pump looks not more than several years old and appears to have been replaced at some point in the past. I was quite surprised that the pump "only" has a peak power of 95W and seems to have three power settings: 40W, 65W, 95W. It has always been left at 95W.

All of the central heating pipes were fitted (hidden) inside the walls when the house was built, and they come out of the walls directly behind each radiator. I can imagine that would be a problem for making changes and for maintenance.

Will_D · Sep 2, 2012

As you have an open fireplace, and IF you have access to free logs/timber then consider an inset stove with a back boiler. We live in a 3 bed semi and fitted one 2 years ago.

The cost of the stove plus fitting was €3500 ( in Dublin ). We kept the oil-fired boiler and the boiler was plumbed in with NRVs and a thermostatic pump. The only thing we didn't do was to run a power feed from the fireplace back to the boiler to switch that off when the boiler was lit.

So when we light the stove we turn off the boiler ( or move its time pegs ). It is rated at about 14 kW to the heating and 2 kW to the room. Works a treat.

The secret is free timber!!

Will

sambotc · Sep 2, 2012

Just make sure you confirm you are not in a smoke free/controlled zone before burning wood, also a house that age I would take a guess there is no chimney.

UK Smoke Control Areas - Defra, UK

Are the pipes small diameter micro bore (10mm or 8mm) ?

Do you have tanks in the loft or a filling loop and a pressure gauge that needs topping up every so often, if so how often?

The actual pipework to radiators shouldn't need changing, radiators would more than likely need re sizing if you choose and ASHP (which I strongly advise against) to allow for lower flow temperatures, although some can work on higher flow temps, more energy is required to raise it that bit further and as far as I have seen the CoP is lower.

Your better off getting a local heating engineer in to quote you on what is required. It could be many things including boiler set up/gas pressure/ gas supply size, sludge or scale in the system/boiler, failed controls/boiler components etc.

The long and short of it is, your boiler is a prehistoric museum piece, very little in the way of efficiency was ever considered when it was manufactured so it seems logical that a newer, more efficient boiler and controls should replace it.

Have a look at the Viessmann boilers with weather comp. Vaillant's weather comp are over complicated and to be honest I think they are becoming over priced.

http://www.viessmann.co.uk/etc/medi....File.File.tmp/6ppViessmannweathercompweb.pdf

ATAG make good boilers with built in weather comp software, only the sensor is required as an extra so I am told, but they are ugly as sin so I would advise against if in the kitchen!

Hope that helps

FB. · Sep 2, 2012

sambotc said:
Just make sure you confirm you are not in a smoke free/controlled zone before burning wood, also a house that age I would take a guess there is no chimney.

UK Smoke Control Areas - Defra, UK

Are the pipes small diameter micro bore (10mm or 8mm) ?

Do you have tanks in the loft or a filling loop and a pressure gauge that needs topping up every so often, if so how often?

The actual pipework to radiators shouldn't need changing, radiators would more than likely need re sizing if you choose and ASHP (which I strongly advise against) to allow for lower flow temperatures, although some can work on higher flow temps, more energy is required to raise it that bit further and as far as I have seen the CoP is lower.

Your better off getting a local heating engineer in to quote you on what is required. It could be many things including boiler set up/gas pressure/ gas supply size, sludge or scale in the system/boiler, failed controls/boiler components etc.

The long and short of it is, your boiler is a prehistoric museum piece, very little in the way of efficiency was ever considered when it was manufactured so it seems logical that a newer, more efficient boiler and controls should replace it.

Have a look at the Viessmann boilers with weather comp. Vaillant's weather comp are over complicated and to be honest I think they are becoming over priced.

http://www.viessmann.co.uk/etc/medi....File.File.tmp/6ppViessmannweathercompweb.pdf

ATAG make good boilers with built in weather comp software, only the sensor is required as an extra so I am told, but they are ugly as sin so I would advise against if in the kitchen!

Hope that helps

Oddly, the house is one of the few "modern" (late-1980's/early-1990's) which have a dedicated fireplace and chimney.

Here's a picture of our lovely log fire at Christmas, a couple of years ago - it gives off a different kind of warmth to any other kind of heating, and below it a picture of the chimney from outside (the pic comes from when we had been wondering whether a second solar array could be installed (4-10kWp band) somewhere alongside the house):