New Installing Advice needed

[holy85]

Hi All,

I'm looking to get my conventinal heating system in the house changed to an unvented hot water system.

Condensing Boiler

For the condensing system boiler I'm looking at Vaillant. I can't figure out which one I would need to get. I currently have 11 radiators in the house.

APPLIANCE MAXIMUM OUTPUT
ecoTEC plus 415 15kW
ecoTEC plus 418 18kW
ecoTEC plus 428 28kW
ecoTEC plus 438 38kW

Unvented Hot Water Cylinder

As for the hot water cylinder I've been recommended heatrae sadia or go with the Vaillant hot water cylinder...Any advise on which one is made better, more efficient?

If anyone has any other advise please let me know...also is it a requirement to have the radiators power flushed before installing a new system?..or can I take the raditors off and put a hose through them to clean as much muck and possible?

 

[Space cat]

You should start with a heat loss calculation for your house, which is not a trivial exercise. To do it, you consider each external surface and multiply its area by its thermal conductivity. Don't forget the floor. You also have to allow for air changes. One per hour is desirable and up to ten may be needed in a kitchen. Multiply the total volume of air that has to change per second by its specific heat in Joules per cubic metre per degree C.

When you add them all up you'll get the number of watts of heat loss per degree C of temperature difference. You can reckon on wanting about 21 degrees inside. For the outside, you'll have to make a guess at just how bad it can get in your area. I used -5 degrees. Remember that you can always use additional heaters for the kind of big freeze that only comes around once a decade (though we seem to have had two in a row recently).

You now know how many watts you'll need to keep your house nice and warm in the middle of winter. Add on another 3kW for hot water and you're there.

For what it's worth, we have a three-bed semi with cavity wall insulation, a lagged loft and double glazed windows. I calculated a minimum requirement at 12kW (40,000 btu) but the 15kW boiler was the same physical size and only cost 10% more so I went for the spare capacity. This paid off later when we got the loft converted.

If you can't be bothered to do the sums, go for the 18kW boiler. I really can't imagine any normal sized, well insulated house needing 28kW!

 

[D_Hailsham]

You should start with a heat loss calculation for your house, which is not a trivial exercise.

The recommended method is to use the Whole House Boiler Size Calculator

The 4XX boilers are open vented; the system boilers are the 6XX series.

 

[muggles]

Look at the sealed system versions of the Vaillants, the ones listed are open vented.

As for a cylinder, can't go wrong with an OSO Super S

 

[Dan Robinson]

An imaginative choice of products

OSO SuperS.

Atmos Intersystem HE26.

Insulation insulation insulation.

CM901/907/921/927.

Simple efficient, better than the above.

 

[Agile]

I am wondering why you are asking here when your chosen installer should be advising you on the spot in your house!

The first thing he would need is to do with your water supply!

Tony

 

[Space cat]

-- Whole House Boiler Size Calculator --

Well that certainly takes a lot of the hard work out of it. If only I'd had internet access in 1994.

 

[bell824]

Look at the sealed system versions of the Vaillants, the ones listed are open vented.

As for a cylinder, can't go wrong with an OSO Super S

must agree try changing your boiler to a 600 series much better for reliabilty and similair sizes are available.
11 rads and a cylinder would normally suggest around about 24kw but better calculations to your specific requirement would be better.

 

[holy85]

You should start with a heat loss calculation for your house, which is not a trivial exercise. To do it, you consider each external surface and multiply its area by its thermal conductivity. Don't forget the floor. You also have to allow for air changes. One per hour is desirable and up to ten may be needed in a kitchen. Multiply the total volume of air that has to change per second by its specific heat in Joules per cubic metre per degree C.

When you add them all up you'll get the number of watts of heat loss per degree C of temperature difference. You can reckon on wanting about 21 degrees inside. For the outside, you'll have to make a guess at just how bad it can get in your area. I used -5 degrees. Remember that you can always use additional heaters for the kind of big freeze that only comes around once a decade (though we seem to have had two in a row recently).

You now know how many watts you'll need to keep your house nice and warm in the middle of winter. Add on another 3kW for hot water and you're there.

For what it's worth, we have a three-bed semi with cavity wall insulation, a lagged loft and double glazed windows. I calculated a minimum requirement at 12kW (40,000 btu) but the 15kW boiler was the same physical size and only cost 10% more so I went for the spare capacity. This paid off later when we got the loft converted.

If you can't be bothered to do the sums, go for the 18kW boiler. I really can't imagine any normal sized, well insulated house needing 28kW!

Thanks for the detailed explanation, that should help me get a better understanding of what I should be looking to get. Once I get the result I'll compare it against the plumbers recommendation. I don't want to end up spending loads on a boiler that wasn't right.

 

[holy85]

You should start with a heat loss calculation for your house, which is not a trivial exercise.

The recommended method is to use the Whole House Boiler Size Calculator

The 4XX boilers are open vented; the system boilers are the 6XX series.

Thanks that should speed up the process

 

[holy85]

I am wondering why you are asking here when your chosen installer should be advising you on the spot in your house!

The first thing he would need is to do with your water supply!

Tony

I was advised on Vaillant or heat sadia. I thought I would get some advise from other who are installers or user of the systems.

The water supply is going to be upgraded to the 25mm HDPE Mains Pipe.

Also thanks to all those who have posted on the thread . You have given a few other options for me to consider looking into.

 

[Agile]

You seem to be concentrating on brand names.

Its just as important if not more so to ensure that the correct size of each component is chosen.

It reduces efficiency to over rate boilers!

Tony