Gas boiler efficiency

brook_heather

I am currently looking into the high gas usage for my parents house which last year was 132,000kWh (yes I know this is excessive) - this is for a large 7-bed Victorian house with limited double glazing and a large floor plan.  They currently have two old boilers - about 30+ years old I believe made from cast iron and are considering replacing them with one or two modern condensing boilers.  They are currently on a very cheap 3-year fix at 2.5p/kWh which expires shortly so until now they have not wanted to pay for new boilers but their new price will be at the July 1st cap so much more expensive.

I asked them to have an efficiency test done as I believe their current boilers would be in the region of 65% efficient and we could compare the savings with a new 90% efficient condensing boiler.  I have attached a picture of the test done by their plumber but it shows 89% efficiency for both old boilers - is this measuring something else as I don't see how their old boilers can be as efficient as modern boiler?

FreeBear

That 89% figure looks like just the burner efficiency rather than how much energy is being transferred to the water within the CH system. You'd be better off referring to the manufacturer's data on overall efficiency. If they say 65%, then it would certainly be worth fitting a new condensing boiler. With the cost going from 2.5p/KWh to 10p/KWh, the payback time would be fairly short, especially if the parents are getting through 132,000KWh per year.

Raxiel

FreeBear said:

That 89% figure looks like just the burner efficiency rather than how much energy is being transferred to the water within the CH system. You'd be better off referring to the manufacturer's data on overall efficiency. If they say 65%, then it would certainly be worth fitting a new condensing boiler. With the cost going from 2.5p/KWh to 10p/KWh, the payback time would be fairly short, especially if the parents are getting through 132,000KWh per year.

And for Context, my (now seven year old) Worcester Bosch condensing boiler got 98.2% for the same value back when it was commissioned.

tacpot12

What's the long-term plan for the property? Sell it or move into it yourself?  

BUFF

FreeBear said:

That 89% figure looks like just the burner efficiency rather than how much energy is being transferred to the water within the CH system. You'd be better off referring to the manufacturer's data on overall efficiency. If they say 65%, then it would certainly be worth fitting a new condensing boiler. With the cost going from 2.5p/KWh to 10p/KWh, the payback time would be fairly short, especially if the parents are getting through 132,000KWh per year.

& if it was e.g. 65% new you can pretty much bet that it  won't be that now 30+ years later.
If they do go ahead & replace then they will have to not only also update the controls but the system must run at 55C flow temp or below - this may also require changing/replacing old radiators as their output will drop at the lower flow temp. Tbh modern radiators will be more efficient/lower water capacity anyway than 30+ year old ones.
It's probably worth considering a complete system redesign/renewal (or selling the house & downsizing). 

FreeBear

BUFF said:

FreeBear said:

That 89% figure looks like just the burner efficiency rather than how much energy is being transferred to the water within the CH system. You'd be better off referring to the manufacturer's data on overall efficiency. If they say 65%, then it would certainly be worth fitting a new condensing boiler. With the cost going from 2.5p/KWh to 10p/KWh, the payback time would be fairly short, especially if the parents are getting through 132,000KWh per year.

& if it was e.g. 65% new you can pretty much bet that it  won't be that now 30+ years later.
If they do go ahead & replace then they will have to not only also update the controls but the system must run at 55C flow temp or below - this may also require changing/replacing old radiators as their output will drop at the lower flow temp. Tbh modern radiators will be more efficient/lower water capacity anyway than 30+ year old ones.
It's probably worth considering a complete system redesign/renewal (or selling the house & downsizing). 

Yes, new controls will be required, as will TRVs on most (all?) radiators. But I'm not sure the flow temp of 55°C is correct. As long as the return temperature is below 50°C, the boiler will be pushed further in to condensing mode, and thus increase efficiency. Fitting larger radiators has the advantage that you can reduce the flow temperature and still keep the rooms warm (as long as the radiators were appropriately sized in the first place).

Replacing an aging Baxi back boiler here. Have fitted new radiators and replumbed in preparation for a new boiler next month - Even with doing all the work myself (aside from the actual boiler installation), it has proved to be an expensive little exercise. I'd hate to see how much a plumber would have charged.

brook_heather

tacpot12 said:

What's the long-term plan for the property? Sell it or move into it yourself?  

My parents are nearly 80 and have no plans to sell or move out so I guess they will be there until they can't walk up the stairs or one of them passes away....  the old boilers are getting harder to maintain and with current gas prices I think a replacement would break even within a few years so worth doing.  It will eventually be sold - I wouldn't be moving to it as it is a different part of the country to where I live.

tacpot12

Same situation as my parents, although they have a smaller property with just the one old boiler. I've looked at Boxt as a supplier for them, and thought they looked good.  Would your parents be happy with a combiboiler as the losses from old cylinders can be quite large as well.

I've tried to persuade mine to have some sort of insulation installed, at least for the rooms they occupy, but they are worried by the amount of disruption and the cost, but without improving the insulation or fitting larger radiators, you will struggle to get a modern boiler to operating in its condensing mode, so the efficiency of a new boiler still might be only around 80%, which means it might not be worth it. 

FreeBear

tacpot12 said: I've tried to persuade mine [parents] to have some sort of insulation installed, at least for the rooms they occupy, but they are worried by the amount of disruption and the cost

Hacking off plaster back to bare brick is very messy if you are doing a top notch job. To keep costs down, fixing insulated plasterboard to the problem walls shouldn't be hugely expensive. Once the carpets are rolled out of the way and skirting/picture rail removed, it could be done in a day for each room. Wouldn't even need to clear all the furniture out..

Ideally, insulating needs to go hand in hand with good quality windows - If the existing ones are 20+ years old (or heaven forbid, single glazed), they will be a major contributor to heat loss.

A Victorian property with solid brick walls needs a lot of thought before insulating the walls. Just slapping up a bit of insulated plasterboard could trap moisture in the walls and lead to some big problems down the line. Breathable insulation with a lime plaster skim would be more appropriate, but costs considerably more.

hareng

I would be looking why or how 132k kw/hrs are used and addressing that. No matter how efficient, theres monstrous waste there via windows, doors and walls etc.

ie 3 bed detached in a cold area 7233kw/hrs average on a 39 year old boiler unserviced.

Spoonie_Turtle

Is it definitely 132,000kWh - is the meter in m³ and the bill thinking it's in ft³?

It would mean they're still using a lot of energy but more like 45,500kWh instead.

Also are the bills based on estimated or accurate readings?

Obviously you need to get the boiler and insulation sorted anyway, but worth just double-checking that the 132,000kWh is actually correct.