Upgrading regular boiler to a combi - initial advice

elsmandino

Hi there.

I have an old fashioned boiler in my 3-bedroom bungalow, which I am thinking of switching out for a combi - the current boiler is from the 90s!

The boiler is on an outside wall in the kitchen and the hot water tank is an airing cupboard in the main bedroom (which is next to an outside wall).

Just a few initial questions to get the ball rolling:

1. Should I try and get this work done now or until after winter?

2. Will I have to upgrade my current pipework (and even radiators) to work with a combi?

3. Where do people tend to put combis, when they do a straight swap - i.e. is it less work to put the combi where the current boiler is or where the water tank is, or does it literally make no real difference?

Any pointers would be much appreciated.

Ebe_Scrooge

First off, I'd be cautious about using the word "upgrade".  Combi boilers can and do work extremely well in the right situation - usually a "smaller" household.  They tend to be less well-suited to a larger family situation, where they can struggle to supply the flow-rate needed to cope with multiple baths/showers being used concurrently.  But if it suits your needs then they can be a good idea.  To answer your questions:

1.  Makes little difference - it'll depend largely on when your installer is available.  Any "good" tradesman is usually booked up weeks or even months in advance.

2.  Not usually, assuming the existing stuff is in decent condition.

3.  It makes little difference really.  It needs to be on an outside wall for the flue to vent, but other than that it can go anywhere.  Probably makes sense to stick it where the old one is as the gas and water pipes will already be there.  But it shouldn't be a huge job to put it somewhere else if that would be more convenient.  Obviously there would be more work involved as the installer would have to move the gas pipe and cut a new hole in the wall for the flue, and block up the old one - but in principle it can go anywhere.

shiraz99

My initial question to you would be, why change?

If the existing system is working, and I don't see why it wouldn't be, then there probably isn't any good reason to spend £2/3K or more on "upgrading" it to a combi.

To answer some of your questions though:

1. When you do it is entirely up to you, personally I'd only want to do this during the warmer months when I'm not using the heating and don't mind the interruption of service.

2. Yes, they will reuse some of the existing pipework and others, such as for the hot water tank will be redundant and will be capped off. You may need your gas supply pipework upgrading. Your rads will stay as is but this is always a good opportunity to see if they're correctly sized and efficient and replace if necessary.

3, The boiler can be positioned pretty much where you want it as long as it can be accessed by the mains water and gas supplies and can be correctly connected to an external flue and condensate system, but all will depend on the prevailing regulations. Speak to your installer.

elsmandino

Thanks very much for the initial advice - really helpful.

As to why the change - a couple of reasons, really.  Firstly, we are thinking of selling in the next year of two and a combi boiler (at least from what I have read) appears to a net gain in property price in comparison to the outlay.

Also - the extra space would really help us out as the property is pretty small and the removal of the water tank and the tank from the loft would really help.

Good to know that the time of year does not really matter - I was perhaps overthinking price/demand and could not really work out when prices would be perhaps cheaper.  

Ebe_Scrooge

elsmandino said:

As to why the change - a couple of reasons, really.  Firstly, we are thinking of selling in the next year of two and a combi boiler (at least from what I have read) appears to a net gain in property price in comparison to the outlay.

Unless your existing boiler is really on its last legs, I wouldn't bank on being able to recoup the initial outlay on the selling price.  Also, it depends on the target market for the property.  As I mentioned earlier, if the property is being bought by a single person or a couple with no kids, then a combi can be an attractive option.  If it's a family with kids, it could actually put some people off.  Added to which, combi's tend to be a bit more complicated than a conventional boiler, with more bits to go wrong.

elsmandino said:

Also - the extra space would really help us out as the property is pretty small and the removal of the water tank and the tank from the loft would really help.

That can undeniably be an attraction of a combi - although, with the loss of the hot water tank you do lose the "warm airing cupboard".  That may or may not be a consideration.  Yes you'll have more space, but you won't get the "warmth" element of it.

(That, of course, leads on to the perennial argument of "Well it was wasted heat, so we're saving on wastage".

"Ah, but it's not really wasted, as it heats the fabric of the house anyway".

"That's good in Winter, but I don't want the house heating in the Summer" ...... )

daveyjp

The first job is to get a proper survey of the existing installation to fully understand what a boiler swap will mean in terms of removing redundant fixtures and fittings, pipework, new flues etc, decorating afterwards.

If you are used to having lots of hot water quickly the combi should be sized for hot water delivery so you need to know your cold water flow rate and match to that.  Easy to do.  Time how long it take to draw a couple of litres of water from a cold tap and from that calculate litres per minute.

Boiler specifications tell you the max hot water flow rate, so go for a boiler matched to the flow rate.  I.e if its 12 litres specify a 13-14 litre per minute boiler.  If your flow rate is less than about 8 litres a combi may not be the best option.

Eg a 24kw will heat about 9 litres a minute, a 30kw 12.  For 15-18 litres you will be up to a 35-38kw boiler, but you then need to consider the physical size of the boiler and the price.  For higher outputs you may need a gas pipe upgrade from 15mm to 22mm.

May not apply to you, but combis generally don't work with power showers.

You will probably need a powerflush, check the boiler warranty. You may find Powerflushing identifes radiators which need replacing due to excessive sludge build up.

I'd also look to spring for the work to be done.

elsmandino

Really interesting that I don't necessarily need to upgrade the piping for my radiators.

I watched a few youtube videos and I was under the impression that new combi boilers have to run at a lower temperature, for environmental reasons, meaning that you need a higher flow rate to get the same heat from the radiators (which means a larger bore of the pipework to the radiators).  Is that not, then, the case?

daveyjp

Combis need to be able to heat a room with a heating water circuit set at 55 degrees, in some cases this may mean radiator upgrades.  Boilers don't need much heating capability to heat water to that temperature.

This is a separate issue to the hot water flow rate from the tap, which is generally important to most homeowners, especially for filling baths and showering.

BUFF

elsmandino said:

Really interesting that I don't necessarily need to upgrade the piping for my radiators.

I watched a few youtube videos and I was under the impression that new combi boilers have to run at a lower temperature, for environmental reasons, meaning that you need a higher flow rate to get the same heat from the radiators (which means a larger bore of the pipework to the radiators).  Is that not, then, the case?

New Building Regs in England have that for new installs (yours would be a replacement) they have to be able to run with flow temp. of 55 or lower. This lets the boiler condense the vast majority of the time which improves efficiency (so save you money & the planet).

On a replacemnt, if you are running lower temperature water through the existing radiators than previously then you may have to run your boiler longer (but it is running more efficiently). It just means that you have to adapt to take that into account - if you have a regular building usage pattern you adjust the time that your boiler comes on to slightly earlier (if you get weather compensating controls it will automatically do so according to the weather outside), if you are erratic & rely on switching the heating on only when you come in it may/will take longer for the space to heat than previously.

As has been mentioned, in the next replacement cycle (10-15 years?) the building will almost certainly require some form of hot water storage.
Combis are less efficient at heating hot water than regular/system boilers.
If I were looking at buying your house in 2 years I would be more interested in it being a  new, high efficiency heating system+controls (all hopefully still under warranty) than whether it was a combi or regular/system boiler..

grumbler

elsmandino said:

 I was under the impression that new combi boilers have to run at a lower temperature, for environmental reasons, meaning that you need a higher flow rate to get the same heat from the radiators (which means a larger bore of the pipework to the radiators).  Is that not, then, the case?

I'd say that at a lower temperature you need bigger radiators in the first place.

victor2

We had our very old (last century!) boiler and hot water tank replaced by a combi a year ago. Floor standing boiler in the utility room was taken out and the new combi went on the attached garage wall, immediately behind the utility room. It wasn't an outside wall, but close enough to one for the new flue to run horizontally out to the wall. Existing water, gas and drainage were all nearby. We did add a radiator to the utility room as we used it to dry clothes in, and it was always warm thanks to the old inefficient boiler!

We had (still have) an electric shower and the hot water tank was basically an expensive airing cupboard. Plans are now to remove that cupboard and have a dedicated shower running off the combi in its place.

Nice to get rid of the cold water tank(s) in the loft plus the central heating header tank. Existing radiators were flushed and no problem found, so no changes apart from the additional radiator. Combi was initially set to heating temperature of 70, which I've dropped to 60 now and the house is getting heated just fine, but it's been pretty mild so far. Rolling year annual gas usage has dropped by over 30%, mainly due to not heating a hot water tank. We were more comfortable last winter with the new system than before, as it has a programmable thermostat, so we have better control.

The boiler has a 10 year manufacturer's warranty, so long as it is serviced annually. I don't suppose it will last as long as the old one, but the warranty makes us think we'll get at least 10 years out of it.

Only irritation is it takes forever to get hot water through the kitchen tap, which I assume is because the water flows through the old pipe system from the boiler in the garage upstairs to where the hot water tank was and back down again to the kitchen.