Vaillant ecoTec 937 Boiler

gonzoelec · 20 Oct 2009

Hi All,
I'm sorry if this has already been covered but I'm a bit confused

, I'm looking at getting a Vaillant ecotec 937 boiler to replace my old boiler (that I think still runs on coal

), the question that I have is that the flow and return pipes that come out of the Vaillant boiler are 22mm and the flow and return pipes on my rads are only 15mm, will this be ok to connect up the 22mm pipes from the boiler to the 15mm on the rads and why are the pipes coming out of the boiler 22mm?
Would be great if someone could give me an answer for this, I'm not doing the plumbing work myself but I don’t want to be caught out if the plumber says that all the rad pipe work needs to be changed.

Many thanks for your time and help

Dave

bogstandardagain · 20 Oct 2009

The 22mm out and in on the boiler are for the distibution network most of the individual rads comming off this network will be in 15mm. As you are entirely ignorat I suggest you ask aroud for a reliable engineer to check over your system as it may have to be amended. A well designed system takes a few mins to heat up from cold a badly designed sytem hours and is grossly wasteful

gonzoelec · 20 Oct 2009

Thanks for your reply, bit worried now that I may have to have my floor boards taken up as I have just had new wooden flooring put down where all the pipes are run, I only have 7 rads in the house, if I kept it all in 15mm would this cause a problem or would it just take ages for the rads to get warm? Sorry Mr "entirely ignorant"

D_Hailsham · 20 Oct 2009

gonzoelec said:
I'm looking at getting a Vaillant ecotec 937 boiler to replace my old boiler

Why do you think you need such a large boiler? Seven rads does not suggest a five or six bed house with three bathrooms and two ensuite showers.

Have you checked your cold water flow rate and pressure?.

The minimum heating output of a 937 will probably be more than your house requires, so the boiler will never be running efficiently.

gonzoelec · 21 Oct 2009

Morning D_Hailsham: I was looking at the 937 as it has got a hot water storage tank on the back of it, so hopefully wouldn’t run out of hot water,(having two girls who are rapidly growing up and always in the bathroom), we have two bathrooms that they are constantly in use (kids hey), I was also looking at putting a room in the loft so another rad would be added (so that gets rid of the tank in the loft and the hot water cyl), I understand what you mean that the boiler wouldn’t be running at 100% efficient and no you are right I don’t have a 5 – 6 bed house (I have a two bed house with two bathroom and seven rads), could you put me on the right track here as what I should be looking for. Your advice so far has been greatly appreciated and I thank you for you time in replying to me.

Many thanks

Dave

D_Hailsham · 22 Oct 2009

gonzoelec said:
I was looking at the 937 as it has got a hot water storage tank on the back of it, so hopefully wouldn’t run out of hot water

You need to check your mains cold water flow rate and pressure. The rate will tell you how much heat is required for heating the hot water. Reckon on 2.5kW per litre/minute. The pressure will tell you if the flow rate to one hot tap will drop significantly if another hot tap is turned on. The higher the pressure the better.

If the flow rate and pressure are OK, then you will get all the hot water you need, even with two baths running, without the need for storage tank.

I was also looking at putting a room in the loft so another rad would be added

That will add 1 or 2kW to the heating requirement.

you are right I don’t have a 5 – 6 bed house (I have a two bed house with two bathroom and seven rads), could you put me on the right track here as what I should be looking for.

Use the Boiler Sizing Wizard to determine the heating requirement of your house. The answer includes 2kW for the traditional hot water cylinder but you can ignore that as you will need another 2kw for the proposed loft room.

When it comes to selecting the correct combi boiler, the max output is determined by the hot water side. But the lowest output is decided by the heating side. The lower it is, compared to you heating requirement the better. This is because the heating requirement is not constant, it varies with the weather. The calculator assumes worst case, i.e outside temperature of -1C. When it is warmer you do not need so much heat, so the boiler can modulate lower. At 10C you need half the heat.

While you are about it, find out the total heating output of all your radiators. You can use the Stelrad Elite Catalogue to give you a good idea.

gonzoelec · 22 Oct 2009

D_Hailsham
Many thanks again you are really helping me out with this, and giving me load of usefull information, I'll use the two sites that you have given be to calculate my needs, and I'll get a pressure gauge to measure the in coming water, will try and do this over the weekend. Thanks again for all your help and time you have given me.

Many thanks again

Dave

gonzoelec · 26 Oct 2009

Hi D_Hailsham

Well i have used the calc. web site that you gave me and it said that I needed a boiler that was 14Kw, I did a rad check and calculated that the CH was 11Kw so not to far out, so I've looked at the Vaillant boilers and a bit confused I looked the ecoTec Plus 824 that gives me 24Kw DHW and 6.7 - 19Kw CH. I have checked my mains water pressure and it is 5Bar just as it comes out of the water meter in the house on 15mm pipe, knowing that I have got two girls that will prob be in each bathroom at the same it will this give me enought hot water if they were both running a bath and the washing machine was on or would I be over running the supply (dropping water pressure), they do a ecoTec Plus that gives 31Kw DHW and 8.7 - 24Kw CH but I think that this would be to big for what I want.

If you can give me any pointers it would be great and thanks for all the help that you have given me, it's all starting to make a bit more sence now

Many thnaks for your time and Help

Dave ;0)

Agile · 26 Oct 2009

You could downsize your boiler if you put a timeclock on the two girls so that only one is in the bathroom at a time!

Or perhaps just lock one bathroom which only you will use. Since you get up earlier and probably go to bed earlier that will remaove any conflict of HW useage.

You need to measure the CW flow rate in litres per minute. Needs about a minimum of 22 li/min with a residual pressure of 1 Bar.

Tony

gonzoelec · 26 Oct 2009

Thanks Tony,

Will do that tomorrw, measure the flow rate, like the idear about locking up one of the bathrooms but could'nt stand the cat fight that would cause first thing in the morning lol

Thanks again for all your help you are giving me on this

Dave

morrismini · 26 Oct 2009

This boiler only small stored water tanks inside. If you want real high flowrate combi then there is only a few wall mounted options. The ATAG, Ethos (Mikrofil) and the Rinnai TwinFlow. There are other stored water wall mounted jobs like the Alpha CD50, a Glow Worm. There are floor mounted combi like the Worcester Bosch 550.

The 937 is quite expensive for what it is and the cheaper Worcester bosch 40 kilowatt combi matches it and has no stored water and a smaller casing.

D_Hailsham · 26 Oct 2009

Agile said:
You need to measure the CW flow rate in litres per minute. Needs about a minimum of 22 li/min with a residual pressure of 1 Bar.

Where do you get a figure of 22L/m from? You would need a 54kW combi to raise the temperature by 35°C.

Agile · 26 Oct 2009

Until the store is depleted the boiler will give about 20 li/min.

That leaves 2 li/min to refill the toilet.

Tony

morrismini · 27 Oct 2009

Agile said:
Until the store is depleted the boiler will give about 20 li/min.

That leaves 2 li/min to refill the toilet.

Tony

A 937 with such a small water store will not give 20 litres a minute for very long at all. I think it drops to around 14 litre per minute when the store is cold.

Agile · 27 Oct 2009

That is quite true, but the 20 li/min enables a medium powered combi to fill a bath quicker or even to give two short showers at the same time.

Welcome back water Systems.

Tony

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Vaillant ecoTec 937 Boiler

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