Two Combi's for Large House?

[temeraire]

Hi all, this is my first post on this forum. I've been lurking around for a while having a good read for some time now. Thanks to all of you for those litle gems of information. I'd be very grateful for any advice or recommendations.

My wife & I live in a large old house, (5 beds with kids planned). At the moment when the heating needs to be run we are burning over £250 of Gas a month & the house still isn't warm & we're only running the boiler for 5-6 hrs a day, (Cant afford to run it any more).

In fairness the insulation in the house was dire. So we're trying to get that sorted out now before the winter

Our Corgi service guy says our existing boiler has probably got another 10 years life in it but is probably only 50% efficient, BG guys says more likely 45% efficient. If we could run the heating twice as long for the same money it sure will help warm the fabric of the house. At the moment we've got a fully pumped Ideal system boiler with a 200l unvented HW tank. I think the boiler is aprrox 110000 btu, approx 15 years old.

The heating system at present is definately too small for the house with some rooms having no radiators & others which are pitifully small. Using internet & book sources I've calculated the total BTU requirements as 84500 for the downstairs, & 48000 for the upstairs. These are just radiator requirements. Like I said its a big house with high celings downstairs.

Adding 10% for general losses this means a boiler size of approx 160000 Btu or 46Kw.

190000Btu or 55Kw if we use a HW circulating tank.

I have seen that boiler prices over 32Kw go through the roof, I was thinking that we may be better to install 2 more normal sized HE combi's.

We have two bathrooms upstairs & a shower room downstairs. I was thinking of a 32 Kw for the downstairs rads & the upstairs HW, & a 24 Kw for the upstairs rads & downstairs HW. I thought the higher HW flow rate of the 32Kw would help the bath fill speed & shower flow. The existing system is already split into 2 zones upstairs\downstairs. We do have room for the tank, but with a house full of kids I thought we'd just end up continually waiting for HW.

We have an installer\engineer coming in a couple of weeks, but I'd just like to know what were looking for before then, or at least be able to have a reasonably informed conversation with him. I'll be doing the Rad & TRV upgrades, & the pro's will be doing the boiler hook up & commisioning.

I'd be gratefull to know what you guys think. Anybody know what the normal solution for a Kw requirement like ours is? Especially with us not having the Earth to spend on it, Big house, big Mortgage repayments. What can I say the wife fell 'in love' with her dream home so what could I do. Have any of you seen that old Tom Hanks film 'The Money Pit'. I don't see the funny side of it anymore.

Thanks & Brgds, Matt

 

[The Baker]

Cost effective measures like correctly laid loft insulation and folded newspaper pushed into the loose window joints could dramatically reduce your heat input requirements.
Heat lost because of draughts is the biggest energy waster in old property, my house is C1850 so I can sympathise with you.
Even stuffing newspaper around the front and back doors last thing at night helps save on heat loss.
I don’t know what the 45% efficiency figure is based on.
Has any one suggested that you actually have the heat on for longer (24 hours) but have a programmable room stat that would include a set back temperature function so running the house at a lower temperature whilst you are out or overnight.
This could be set up to prevent the building getting so cold that condensation takes place and the building being slightly heated does not feel as unwelcoming whilst not bankrupting you.
Re the boiler size calculation a rough figure can be arrived at by multiplying the volume of the house by 4 to arrive at the BTU,s required. So if a room measured 8hx14wx22l it would need 9586btu output from the rad to keep the room at 65ish degrees when its very cold outside.

Regards,

Tim

 

[Agile]

You say you have an unvented cylinder. You should not get rid of that. It can be heated by a combi boiler though.

As Tim says your priority should be full spec loft insulation and draught proofing. Even if its only cellotape along the window joints during the winter ! Secondary glazing using plastic sheeting and closing curtains all helps.

Only heat the areas you live in and then only while you are occupying them.

With the heat losses properly managed and the zones correctly timed then I would be surprised if you really needed any more than 24 kW.

Many people run up high gas bills because they run undersized rads for long periods hoping they will eventually heat up the house. Thats just feeding the heat losses. Fit a few good sized rads in the rooms you use and run them only when needed and you will have comfort and economy together. Two people only need two rooms heated at any time!

My house has five beds and solid walls and would cost thousands if I heated all of it. I keep the gas bill to under a thousand by only heating the part actually occupied at any time.

Tony