Condenser Fitted into centre of house

[neil.russell11]

Hello

I wonder if someone can help me with a problem. I am currently trying to organise a replacement condenser or combi boiler for my mother who lives in a 4 bedroom semi detached property by herself. 8 rads will be fiited with trc's however we have received conflicting advice based on which type of boiler and where the condensation pipe will go if indeed she has a condenser fitted. The long and short of this is that she currently has a jonhson starley J25-32 ducted air system the boiler is in the kitchen (ground floor) with a hot water tank in one of the bedrooms. the initial idea is to fit a combi condenser (baxi 105 31kw or platinium 33kw) into the airing cupboard where the hopt water tank used to be however one installed is proposing taking the pipe for the waste condensed water out of the wall under the bedroom floorboard then run the pipe about 12 feet along the house horizontally then down to the drain and the other is just saying a condenser is not suitable and she will need a combi boiler as you can only fit condensers to an outside wall. Can anyone advise if they think either of these methods is unsuitable. Also one of the guys seems trust worthy however his father is retired (so has no corgi reg anymore) he is starting and waiting to complete the course so they have advised currently they are having a colleague (who I have confirmed with corgi is registered with them) to inspect install and pass for safety.

Any help greatly appreciated

Thanks

Neil

[Lobster]

Twaddle. Mine is (legally) attached to an inside wall

David

[fred]

Pants indeed, the dribble of condensate can happily be piped away from the middle of the house to a suitable drain. Not sure whether 20mm plastic is suitable for the whole run, I think it may need to be 32mm for a long run with a short fall. There are many condensers designed to be used in apartments with ducted flues running in the centre of buildings.

I think a lot of old school installers are in a bit of a huff with condensers ("we haven't needed to do it this way before") and haven't bothered to get up to speed on the capabilities of these new fangled contraptions.

[Andy Hall]

The first thing is not to confuse the terms "combi" and condensing boilers. A combi boiler is one which has the ability to heat water from the mains directly without the use of a cylinder. A condensing boiler is one which has internals and a control system designed such that there is condensing of some of the combustion products to water inside the boiler. This causes release of additional (latent) heat and results in greater efficiency. Said water has to be piped away.

You can have condensing and non-condensing versions of combi boilers and condensing and non-condensing versions of heating boilers (i.e. those that work with a HW cylinder etc)

So there are two decisions to make. The first is whether she wants a combi boiler and to remove having the boiler in the kitchen and cylinder in the bedroom. Bear in mind that the water flow rate from a combi is unlikely to be as great as is currently being achieved from a cylinder and baths etc. will take longer to fill, especially in the winter. The boiler size is upper mid range and would work reasonably well, especially for a person on their own who may not be too concerned if it takes 10-15mins to fill a bath. However, if it is on the radar to move within the lifetime of the boiler and the house is such that a bath and shower in concurrent use is possible, then this may be a consideration and a combi of this size could be marginal for that. One thing that should be checked for a combi implementation is the mains cold water flow rate. This can be done at the kitchen sink with a bucket, a stop watch and a calculator. One thing that is common in houses with a roof tank and cylinder is that only a 15mm pipe is used from the stop tap to the roof tank. If this is the case, then it may need to be replaced with a 22mm pipe.

On the condensing/non-condensing question, it is certainly not the case that they can only be fitted to an outside wall. manufacturers have gone to a great deal of trouble to provide solutions to address fitting in other places.

For example:

- For many models, flues can be concentric pipes or separate intake and outlet types. With some, flues can even be constructed with 50mm high temperature waste pipe and run over tens of metres.

- Condensate production is usually no more than a trickle and can be run through plastic pipe. The distances mentioned are relatively long, so the important thing would be to make sure that there is some slope, especially more so outside, to prevent water laying and freezing.

- There are condensate pumps. These are used normally when a boiler is installed where the drain is higher - e.g. in a cellar - to raise the water to an outside drain level. However, another option could be to run the condensate pipework across the loft and join a soil stack. Pumps cost a few tens of pounds and perhaps this could provide a neater solution?

The second installer may be a bit of a Luddite or may simply be trying to suggest a lower cost option, or may simply have no experience of condensing boilers. This is ridiculous really, because there is only the issue of the condensate drain that makes the difference anyway. There is a medium to long term cost saving with a condensing boiler in terms of running costs and a reasonable assumption that gas prices will increase.

You can refer to the exemption rules at the ODPM web site, where there are details of an assessment procedure.

This leaflet is useful as a guide to that plus some installation suggestions.

may be that the criteria for not having to have a condensing boiler could be met if she wanted to go that way.

Semidetached house 590 points New boiler in different room 350 points Extended flue > 2m 200 points

Total is 1140 (greater than 1000 limit) just with these things, so she doesn't *have* to have a condensing model if she didn't want to do so (assuming new flue is >2m).

[Doctor Drivel]

Tripe! high flow combis are available equalling any cylinder setup.

[neil.russell11]

thanks for this , what's a stack by the way? can you also tell me how to do the water flow calculation

[Andy Hall]

Read the whole thread and the context. The products under discussion are not "high flow". They are in the average range. The 33kW one does the predictable 13 litres per minute. This may be fine for the user or it may not, but it is sensible to take all of the potential issues into account.

[Andy Hall]

You're welcome, Neil.

The stack means the soil stack, although obviously you need to look at the design rules in the PDF file. If this is on the inside of the house, it may be worth considering, otherwise probably not. I was simply thinking that generally getting things through a loft space is a lot easier than under floors, and could be a way to avoid having 4m of waste pipe on the outside of the house. Obviously it depends on the arrangement of the house etc.

To calculate the flow, take a container (e.g. bucket) of known capacity. (e.g. 5 litres). Using the watch, time how long it takes to fill from the sink cold tap.

Example: If it takes 15 seconds to fill a 5 litre bucket, then that would be 4 times a minute and the flow rate is 20 litres per minute.

You could do this using a 2 litre measuring jug, but it's not as accurate as a larger container because of the difficulty in accurately checking the watch.

It's worth repeating the test a couple of times and averaging the readings.

Note also that it will vary somewhat during the day.

The water suppliers are only legally required to deliver 9 litres per minute, and obviously this could be disappointing in comparison with the existing system.

Generally as long as there is about 20 litres/min or more, then results are reasonable.

Keep in mind that the quoted combi flow rates are for a 35 degree rise in temperature, so in effect in the winter this will be the total hot flow rate for bath/shower temperature (when mains cold is in the typical 5-8 degree range).

If you want to be scientific, you could measure the current flow rate into the bath and also time how long it fills to normally used depth. Then you can calculate how long it would take with the flow (possibly) limited to what the mains can do, or what the combi can do.

If mains flow rate turned out to be an issue, then options are to get the pipe from the street upgraded (could be expensive), or stick with roof tank and use that to supply the combi.

If the combi is felt to be inadequate but the idea of a box in the airing cupboard appeals, then there are larger combis than 33kW and also appliances which store some amount of hot water within the boiler itself (Powermax is an example of this and there are a number of others). Look for "Combined Primary Storage Unit".

Don't be concerned if the appliance rating appears to become large in relation to the heating needs of the house. In heating mode, the boiler will reduce (modulate) its output down. The full power is required for water heating, and for basic combis which don't store water, the HW production rate is directly proportional to the appliance rating.

It may well be that the type/range of combi is entirely suitable - probably is for a single person who is not time constrained. However, the whole project is a substantial investment, so an hour spent doing the homework and checking does make good sense.

[Doctor Drivel]

You said "baths etc. will take longer to fill". Which is tripe. High flow models are zippo. You are spreading amateur myths.

[Andy Hall]

I'm sure that everybody else, including the OP understood the point, but since you seem to want to be obtuse, let me spell it out for you:

- A 33kW combi of the type under discussion will deliver 13 litres per minute of hot water with a temperature rise of 35 degrees.

- The temperature of the cold mains in the winter can be in the region of 5 to 8 degrees

- Since usable shower/bath temperature is in the 40 to 45 degree range, it follows that the filling rate, for this type of boiler, at this rating will be 13 litres per minute.

- An existing storage system holds water at 60 degrees. It is mixed, when running the bath, with cold water from the storage tank or the mains to produce water at the required temperature.

- Each of the cold and hot flows of the storage system are likely to be at least at 13 litres per minute if they are piped using 22mm pipe (the standard). 20 litres/min is quite typical, and I suggested to the OP that he might like to measure it if this might be an issue for the user.

- In any event, it is highly likely that the boiler type under consideration will fill the bath more slowly than the existing system. Whether that is an issue for the user can then be determined.

- Therefore my comments, in the context of the appliances being considered were entirely correct.

- I am fully aware that there are higher capacity instantaneous combi boilers available. However, within the realms of available gas supply in a domestic installation, once other requirements such as cooking and other appliances are considered, it likely that the limit for a boiler will be in the 40-45kW range. It is not a coincidence that this is the largest model size of this type of product for the UK market from the larger vendors. Predictably, these will produce around 16 litres per minute.

- Beyond that, as I also mentioned, to achieve a greater HW production rate than achievable instantaneously, some form of energy storage is needed. This can be done externally to the boiler, viz. a conventional cylinder, heat bank or thermal store; or within the appliance as some form of CPSU. The performance of these depends on the amount of water stored and at what temperature.

[Doctor Drivel]

Matt, the point you made was clear and incorrect: "baths etc. will take longer to fill". Which is tripe.

Matt? Obtuse? I said: "high flow combis are available equalling any cylinder setup" Wow that is obtuse.

Matt, please don't you haven't a clue that is clear

[Dave Plowman (News)]

Don't know why you bother, Andy.

The cretin just doesn't understand figures.

My bath fills at approx 40 lpm (hot and cold together) to a piping hot temperature - regardless of the state of the incoming mains water - from my storage system.

There ain't a domestic combi that can match that.

[Doctor Drivel]

Mr Cranium, if matt wants to bother he can.

So 20 litres/min on hot water, the same as many combis. And no high pressure showers, and tanks and cylidners all over the place with a combi.

Many are way above 20 litres/min. The Gledhill Gulfsteam floor mounted combi delivers 45 litres/min of "hot" water. The MAN Micromat 76kW can deliver over 30 litres/min - for ever. The ACV Heatmaster pours out the hot water flowrate.

[Andy Hall]

20lpm of hot at 60 degrees plus 20lpm at mains temperature is not the same as 20lpm at 40-45 degrees.

This a CPSU and has storage.

Requiring more than a standard domestic gas supply can deliver.

This is also a storage device.

If you are going to make arguments in the direction of these kinds of appliance, at least do so honestly with all of the factors involved taken into account, and not just the ones that suit you.

[Dave Plowman (News)]

Sigh. 20 lpm at 60C, cretin.

[Doctor Drivel]

Oh senile one, still way below the 45 litres/min the Gledhill can pour out.

[Doctor Drivel]

Matt, still way below the 45 l/min the Gledhill can pour out.

Matt, It is a combi, see sedbuk. It is a one-box solution.

Not an issue, Matt.

Matt, it is a combi, a on-box solution.

Matt, these are high performance models. The ones which don't exist and can't pour out the flowrates according to the amateurs on this ng.

[Dave Plowman (News)]

With upgraded water and gas mains supplies. Do you have any idea about value for money, cretin?

Oh - and you're saying it will provide 45 lpm at 60C?

[Doctor Drivel]

No gas upgrade and many supplies can deliver 45 litres/min.

[Dave Plowman (News)]

Many, eh? Please quote the minimum spec for a mains water supply. Cretin.