Replacement 60Kw domestic boiler

[glojo]

We are about to replace our old Potterton Kingfisher CF180 boiler with something ‘slightly’ more efficient and I am confused with all the different options being offered. We live in a large detached house which has a heated indoor swimming pool.

It has been calculated that we will need a 60Kw boiler to cope with heating the hot water, twenty radiators and the indoor swimming pool. I am told the house needs approximately 20Kw and the pool 40Kw of heat which hopefully adds up to the 60Kw.

I am leaning towards a Viesmann boiler\boilers and would appreciate any advice folks might have for the best option.

Should I opt for a single commercial boiler or two 30kw domestic units?

If I go for the two domestic units then is it possible to have the boilers work intelligently? In other words if I only want the hot water to be heated then is it necessary for both boilers to operate or is there something that would be able to determine how much heat is required to carry out a specific task? Is there something that can work out the most efficient way to operate two boilers and would this be more economical than having one commercial boiler?

The central heating is an open system at present but I would prefer to have it converted to a sealed system but is this a big job as one of the quotations is talking about this needing an autofil system because the job is over 45Kw.

The pool is mainly heated during the hours we are all in bed which means that the heating comes on when the central heating is not working although it will operate when we are actually using the pool.
I am getting quotes for the job, but each person is coming up with different suggestions and I guess I am trying to get independent advice from folks that are not involved.

I am opting for Viesmann solely because of their reputation and the five year warranty, so please feel free to offer alternative ideas.

Price is secondary to efficiency and reliability

 

[mickyg]

I'd have 2 domestic boilers. 1 to do the pool and 1 to do the heating and hot water in the house. Sealing it will be no problem.

 

[glojo]

I'd have 2 domestic boilers. 1 to do the pool and 1 to do the heating and hot water in the house. Sealing it will be no problem.

Hi Mickyg,
I have had the recommendation of using two boilers working together to help eliminate any possible break down issues. In other words if one boiler breaks then the second boiler could still cope to a certain degree and at least give me hot water and keep the house warm.

If one boiler was just designated for the pool then this option would not be available to me.

Please understand I am NOT saying I am right... You are wrong.
I am hear solely to listen to what is being said and pass on any comments\observations.

Mysteryman
Thank you for the input and I am guessing that a 60Kw Vitoden would be cheaper than the commercial Viesmann boilers.

I did try contacting Viesmann UK but all they did was give me the telephone numbers of my local installers. I have contacted these folks and am getting different suggestions which is 'making my head spin'

By getting independant thoughts I am hoping to slow my head down.

 

[WhydidIstart]

Hi, I’m not a plumber, but I do design and work with large control systems. For important projects redundancy will always be used. So although two boilers may have more parts than one, using two boilers gives the availability of the other one when one breaks down or needs servicing.

From the description of your house and your research here, it sounds like you are looking for the best system and not just the cheapest or easiest.

If true, it would seem to make sense to have two boilers connected in parallel such that either one could be used to heat everything; your house, pool and DHW. My feeling would be to have a ‘primary’ boiler that normally operates when house heating or DHW is required and the second boiler in standby until the pool heating is also required. When the pool heating calls for heat, both boilers would then operate in parallel and be able to deliver full available power to your pool.

You would have a switch to enable the standby boiler to work at the same time as the primary one – this would allow the secondary one to heat your house and DHW if the primary boiler fails and also could be used in severe winter for more output as that 20kW calculation will be based on fairly cold weather, not the -17 and below we saw a month ago!

This seems the most flexible approach, providing both redundancy and the ability to use the boilers’ full power to heat your pool quickly, well not as slowly!

 

[WhydidIstart]

Just another thought - you could stick with a normal boiler for the house and use an electric heat pump for the pool. 40kW output units are available and can effectively be 500% efficient, so are cheaper to run as gas is not 5 times cheaper than electricity and is only low 90s% efficient.

If you could get an economy 7 night time electricity rate that would make gas and electricity a similar price and hence make your bills 1/5 the price...

 

[glojo]

You would have a switch to enable the standby boiler to work at the same time as the primary one – this would allow the secondary one to heat your house and DHW if the primary boiler fails and also could be used in severe winter for more output as that 20kW calculation will be based on fairly cold weather, not the -17 and below we saw a month ago!

This seems the most flexible approach, providing both redundancy and the ability to use the boilers’ full power to heat your pool quickly, well not as slowly!

I would be very grateful if you had any links etc

Just another thought - you could stick with a normal boiler for the house and use an electric heat pump for the pool. 40kW output units are available and can effectively be 500% efficient, so are cheaper to run as gas is not 5 times cheaper than electricity and is only low 90s% efficient.

If you could get an economy 7 night time electricity rate that would make gas and electricity a similar price and hence make your bills 1/5 the price...

Another great idea and is this a sort of calorex heat exchanger and yes we are on economy 7

I guess we can see why my head is spinning but I appreciate all these VERY useful suggestions

 

[mickyg]

firstly, the heat calculations sound the wrong way around. 40kw for the house and 20kw for the pool sounds more appropriate. I look after a couple of boilers heating very large pools(25m) and neither are more than 28kw. Additionally a large house with 20 reasonable sized rads is gonna probably require 30kw+

Anyway, as for using 2 boilers, yes you could either fit them to work in parallel OR fit them seperately with a closed link from the pool boiler in the event the house one goes down. If you fit good quality heat only boilers the likelihood of failure will be very very low anyway. Use external pumps EVs etc, cos anything in a system boiler may be undersized anyway.

Beware of some posters who work for particular manufacturers and will only recommend their products

 

[glojo]

firstly, the heat calculations sound the wrong way around. 40kw for the house and 20kw for the pool sounds more appropriate. I look after a couple of boilers heating very large pools(25m) and neither are more than 28kw. Additionally a large house with 20 reasonable sized rads is gonna probably require 30kw+

Anyway, as for using 2 boilers, yes you could either fit them to work in parallel OR fit them seperately with a closed link from the pool boiler in the event the house one goes down. If you fit good quality heat only boilers the likelihood of failure will be very very low anyway. Use external pumps EVs etc, cos anything in a system boiler may be undersized anyway.

Beware of some posters who work for particular manufacturers and will only recommend their products

Hi again mickyg,
The figures I quoted were those worked out by British Gas Domestic who came to give me a quote for a replacement boiler. Following your first post I have been letting my fingers do the walking and my research tends to agree with what you are saying.

I have checked with a couple of swimming pool sites and the consensus is that 2Kw is need for approximately every 1,000 gallons. Our pool holds approximately 16,000 gallons which indicates I am way out with my first post and only 32Kw would be required. Unfortunately the sites have turned me off of the idea of changing to electric heating..

Electric Swimming Pool Heaters are in many cases the preferred method to heat your pool water as when combined with a Economy 7 supply tariff and solar pool covers they are a highly effective method. They are slightly more expensive to run than gas heaters, however they are very efficient and are suitable for all types of swimming pools.

The heater will operate at night on Economy 7 at the same time as the filtration period of about 7 hours. The control circuits measure the temperature of the pool water and supplies just the right amount of heat to ensure is up to the desired temperature the next morning.

The house is quite large and also at the top of a very exposed hill plus the pool is kept at a constant 32 degrees centigrade

 

[mickyg]

dont even think about using electric unless you have alot of shares in your electric company!

"slightly more expensive"

 

[glojo]

Should I opt for a single commercial boiler or two 30kw domestic units?

I have asked lots of questions, listened to what has been said and during my enquiries both via Google and the good old fashioned telephone, I have now reached a decision

The two 30Kw boilers were a tempting option but I just feel it is asking for long term problems regarding maintainance, reliability etc.

I guess I will be buying one 60Kw condensor boiler plus a weather compensator.

I made very brief enquiries regarding solar heating and that is something that would never re-coup the costs and so that idea has instantly been binned.