Piglet - another boiler question!

[weakestlink]

I am still stuck on the lack of external wall space - only option in kitchen would only leave a 3cm gap to the window...

Does the boiler itself need to hang on the external wall or could it be near the external wall and then the condendation piped out to the drain?

the flue can be ducted to an external wall, sideways or backwards or upwards, or a combination.

the condensate pipe need not and preferably should not go outside, in most cases it can be connected to the same waste pipe as the sink and/or dishwasher and/or washing machine.

I don't know what dimensions you have. Mine is a Viessmann 100 Compact which is very small and is in a corner of the kitchen (not a combi, needs a cylinder, though they make combis as well) and the current version has a very good reputation and guarantee. see page 6 dimensions and flue pages 14 and 15

They say the flue can be up to 19metres long but there are various reasons why this would be impractical in a typical UK home.

I think mine is even smaller as it is the open-vent version with no pressure, but I can't see it in their doc.

I have no connection with the company. No doubt equivalent products are available from other manufacturers.

What are the dimensions of your space? How big is your home?

found it

the vented models up to 18kW are 600x375x285mm H/W/D

the 26kW and 35kW (for quite a large house) are 600x375x340

Of course this does not mean it is neccessarily suitable for you and your home. The combis are always bigger.

Hi Piglet - looks like all will be well - the boiler can go in the kitchen like you suggested and the flue ducted sideways to the extermal wall. Gas will have to be re-routed though which will mean some slabs coming up but that's not the end of the world.

Boiler suggested is this or I can research 30kw combis myself.

To give you an idea of size of house we have 4 bedrooms, 2 bathrooms (1 bath 2 electric showers) and another cloakroom downstairs, 2 large recs, 1 study, kitchen, utility, porch. Does 30kw sound reasonable?

I am to buy the boiler and rads myself directly after consultation with engineer (to keep him under vat threshold I imagine?) Suits me anyway as I can shop around.

It was suggested that we wait until March as January is too cold and he is on holiday all of February. He is going to come round after Christmas to give a price for labour and confirm sizes of rads I need to order.

This chap is a trusted gas safe chap from our village who we know well so I will most likely go with him but I will get in a couple of others to quote for comparison...

All sound ok?

Worcester Bosch are good boilers and it will deliver about 12 litres per minute of hot water provided your incoming main and internal pipes are big enough (fill a bucket at the kitchen cold tap, time it, and calculate how many litres per minute you receive.

However, you have a medium sized house with two bathrooms. The combi can only deliver a limited amount of hot water at any one time, so if you are running a bath or shower and someone turns another tap on, the flow at each tap will halve.

Do you currently have a cylinder? Measure the hot bath flow with your bucket and consider how you will be affected. Heating engineers like fitting combis because it is a fairly quick and simple job.

It is actually possible to have a modern system boiler feeding a cylinder (or a Megaflow if you have a very good cold water supply, or can get one by upgrading the supply pipe to the main under the pavement).

A combi can be piped to heat a cylinder as well, giving you both instant powerful showers, and a good supply of bathwater. The heating engineer will know how to do it, though it is less common. Filling a bath from a cylinder means you are not limited by the 12litres per minute since the hot water is stored prior to use.

Yes we currently have a cylinder downstairs in a cupboard..... I will mention all this when he comes in January then.
How much extra are we talking to add a cylinder to the combi system? If not too much then this sounds like a good option.

Presuming the cylinder could be housed in the same place as the current one.

you could keep the old cylinder if it is reasonably modern (should have a coating of stiff plastic foam in yellow, (better) green or (best) blue). Older cylinders do not heat up as quickly. A modern boiler can heat a modern cylinder in twenty minutes.

A Megalflow is superior, but you do need a very good incoming water flow as there is no loft tank. It is a pressurised stainless steel cylinder that runs at mains pressure. It hasd to be installed and serviced by someone with an extra qualification and certificate in pressurised cylinders.

An advantage of a cylinder is that you can heat the HW with an electric immersion heater when your boiler breaks down (which it sometimes will). combis break down more often than conventional boilers, but this is partly because they are more complicated and have more to go wrong, and all the parts are inside the boiler case instead of having a separate pump, valves, tank etc.

Yes it is blue :)

I think our incoming water flow is fair but not excellent. Have lived in houses where it's better.

Will aim for keeping the cylinder then...

bucket, tap, timer?

Am in the office today... but will do it tonight.

in a somewhat smaller house (3 bed terrace with attic, 1 bathroom & 1 shower room) we have \link{http://www.onlineboilers.co.uk/combi-boilers/worcester_bosch/greenstar_junior-28i/100281\the next one down from your 30si,} weakest link. the main difference is in water flow rate - 11.4 litres/min vs 12.3 litres/min for yours

fwiw we've had up to 7 adults in the house occasionally over the last couple of months & it's been more than adequate. (I do love having a combi & never having to worry about the hot water running out when that many people all feel the need to have a shower or bath in quick succession )

PigletJohn, while you're here, I wonder if you can answer a question for me? Our boiler has different settings for radiator temp & I've recently turned it up from 4 (68) to 5 (74)

Long term, does this mean the boiler uses more gas, or not? Presumably it'll have to run a bit longer to get the radiators up to the higher temp; but then once they are, won't room stat temperature be reached more quickly, so the boiler will cycle off sooner than at the lower radiator temp?

a modern condensing boiler runs at its most efficient at about 60C flow

If you can find the spec for your boiler, it will probably have a % efficiency at 60C and a % efficiency at 80C, and the 60C will be better.

It may be that in cold weather like this, your radiators are not big enough to output enough heat at 60 so you need to increase their temperature. Or did you turn it up for some other reason?

I am sure the boiler itself has more than enough power. I bet if you calculate the heat loss from your house it will not be more than 12kW

Having a boiler cycle on and off is less eficient that letting it tick along at a lower setting. It will modulate its flame size down to match the heat output required, which also improves efficiency.