Help Estimating Boiler Size

[Scol]

Hi All,

First post ....

I am in theprocess of renovating a Large Victorian farm house and need to select asuitable boiler or boilers to provide heating and hot water.

The boiler willneed to run
·31 radiators totaling circa 105k BTU (30.7KW) on two circuits
·1x Large and 1x Small Under-floor totalingcirca 30k BTU (8.8 KW) on a third circuit
·Hot water to 2 full bathrooms, kitchen,utility and 3x WC’s

As there is nomains gas, the boiler will need to run on LPG (have ruled out oil due tosecurity concerns).
We would likehot water to run at mains pressure so we are looking for a system boiler.

The house hasjust be re-roofed and the loft insulation has been brought up to currentstandards, the windows are largely single glazed original Sash’s, however they havebeen draft proofed. The walls are a mix of single 9” brick and cavity designbut with no cavity wall insulation.

I was originallyadvised to have a twin boiler system but have subsequently been told by myplumber that he recommends a single semi-commercial boiler rated at between 80and 100kw. He has told me that this will both future proof the system againstany increases in demand (none planned in the life span of the boiler) and ensure that the boiler is notstressed which makes sense but I cannot help thinking that it is a bit OTT andthat something closer to 40-45KW would be more appropriate and quite possiblymore efficient.

Any advice/thoughts would be really helpful.

 

[Worcester]

See the threads on heat loss calcs I've done somewhere.

If you've got the space your best choice would be either a gassifcation log boiler, or for automated operation a pellet boiler (with buffer). The DomRHI will pay you back for the capital costs of the installation, and your ongoing fuel costs will be in the region of 50% less than LPG.

LPG is an incredibly expensive choice.

You need a heating engineer not a plumber.

Where are you in the country - nearest town (and county) will do!

 

[Worcester]

http://www.ukplumbersforums.co.uk/central-heating-forum/64061-heat-loss-calculation-software.html

That'll give you a guide

 

[Nostrum]

80 - 100kw is ridiculously oversized.

I would suggest finding another plumber or even better getting a heating engineer!

I would question the heat loss calc's firstly. Then I would seriously suggest looking at a pellet or log boiler installation as Worcester has suggested. It will cost you more initially, but will pay for itself when stacked against the running cost of LPG and RHI payments for 7 years.

If you do decide to stick with LPG, 2 smaller boilers would be much better suited as it allows for a wider modulation range.

 

[Worcester]

Knew there was a big discussion about it all somewhere, read this thread (all of it as well: http://www.ukplumbersforums.co.uk/c...izing-rads-lower-circulation-temperature.html

 

[kris]

100kw is over kill but you have 31 rads and with a house that size i dare say quite a few bathrooms so couple hot water tanks, you said 2 bathroom but is there any en suites as still need to include them,, so i reckon his lower region of 80 wont be too far off , me at a guess would say 70kw but do calcs or send figures away for heat loss calcs,,,

 

[morganb]

If you've got the space your best choice would be either a gassifcation log boiler, or for automated operation a pellet boiler (with buffer). The DomRHI will pay you back for the capital costs of the installation, and your ongoing fuel costs will be in the region of 50% less than LPG.!

Worcester, is this a rough estimate to say the ongoing RHI payments for 7(?) years will overall pay for the initial install, then it's just a case of comparing fuel costs.

 

[Worcester]

When did you buy the house? If within the last few years it will have had an EPC done, if within the last 18 months then that will tell you what the energy requirement for the property will be, a few quick cals back from that and you've got a very rough idea of the kW boiler you'll require.

So, when did you buy the property?

 

[Worcester]

@morganb, Yes.

In almost all cases with biomass the DomRHI plus allowance for the fact the boiler needs replacing will fully cover the cost of the install including an allowance for borrowing the capital to pay for it.
- That is exactly the parameters that have been used to calculate the DomRHI tariffs.

The fuel saving is a massive bonus

GSHP similar results, ASHP you need to add in the fuel savings to show the financial benefit (other than the eco credentials )

 

[chris watkins]

Get yourself a new heating engineer or better still pay to have the designs done by a consultant, otherwise you are going to come unstuck !!!! (You do not oversize boilers)

You can't tell us in one breath you need 30.7kW & then go on to describe the glazing & wall contractions as these have all been taken into consideration when the heat loss calc's where done, weren't they ???????

If you don't what to go down the re-newables route (& I think you would be mad not to in one form or another) then I would look again at the running costs for LPG over oil you might think again.

 

[Nostrum]

100kw is over kill but you have 31 rads and with a house that size i dare say quite a few bathrooms so couple hot water tanks, you said 2 bathroom but is there any en suites as still need to include them,, so i reckon his lower region of 80 wont be too far off , me at a guess would say 70kw but do calcs or send figures away for heat loss calcs,,,

Allowing 30kw for water is a tad above and beyond!

 

[Worcester]

Allowing 30kw for water is a tad above and beyond!

Me thinks he was suggesting make it a 70kW Combi running 28mm DHW pipes :29::waving:


Come back Scol, all is forgiven

 

[Scol]

Dear All,

Thanks so much for the responses, to pick up on a few of the questions asked:

I have chosen LPG for security (recent oil thefts in the area) and because the property will not be occupied full time so running costs are not such an issue. I also like the fact that the tank will automatically initiate a top up when running low and that I can control everything remotely The tank is installed and filled so no going back on this one.

The Energy Effeciency Rating for the house was E (47) with a potential of C (79). Since this was taken though we have removed secondary double glazing and had the sash windows restored and draft proofed. We have had the loft insulation brought up the current standard and are adding insulation to some of the external walls. When determining the capacity for the rads and underfloor, all of this and more was taken into account using available on-line calculators.

The property has one full bathroom, one full En-suite (with over-sized spa bath), Kitchen, Utility and 3x WC's.

The property is located near Peterborough.

So, assuming that the calculations for the heating are correct, how much capacity do I need to allow for hot water?

Any thoughts on actual boiler/s for this application?

Thanks so very much.

 

[Scol]

Sorry for the delays, my posts are having to be vetted by the moderators which is fair enough of course.

 

[morganb]

If you must go LPG it's better to get two smaller boilers rather than one large. In the event one of them breaks down you still have the single boiler working that can provide part/all of the heating/ho****er demand.

Also 31 radiators seems a few to many in only a 2 bath house, especially with underfloor heating. I suppose it can vary greatly with layout etc.

 

[Dotty]

Be careful here, you're very nearly in commercial territory (there's no such thing as 'semi-commercial'.) And as such you'll need a commercial engineer.

And we're incredibly expensive.

As said before get a heating engineer in to design it properly or you'll end up with a white elephant.

 

[Nostrum]

What's the floor area of the property?

If you have a 40kw boiler which would suit your heat loss then there should be no need to add any additional allowance for hot water.

In a situation like this, I think I would look at a 40kw combi. It will be adequate for the space heating, you could run the kitchen taps off the combi side, then using an S plan plus arrangement of controls I would zone the underfloor heating, the radiators and a suitably sized cylinder. (how many occupants?)

this is way you could run the underfloor continuously as required if it is in a screed type floor to keep the slab warm, radiators as and when (layout dependant) and hot water when required. Being a combi you will still have instant hot water at whichever outlets you choose (WC's & kitchen for example) when the cylinder is cold, saving money by not heating the cylinder until required for showering/bathing.

 

[Scol]

Thanks Morgan B,

There are 5 bedrooms and 4 reception rooms + utility, boiler room, store room office, kitchen, hallways, WC's etc etc + all of the rooms are quite generous size wise. The underfloor is just for the kitchen and office though, rads everywhere else.

Ok, so a twin boiler system seems like the way to go then but what overall output should I be looking for?

Thanks

 

[lame plumber]

never even consider lpg in a property your size its a no no whatever the security issues, nicking lpg would be just as easy for anyone in the know and very worth while! Plus the fact our idiot government is willing to pay you to put in a pellet burner or other such CO2 reducing form or heating system

 

[chris watkins]

never even consider lpg in a property your size its a no no whatever the security issues, nicking lpg would be just as easy for anyone in the know and very worth while! Plus the fact our idiot government is willing to pay you to put in a pellet burner or other such CO2 reducing form or heating system

You no listen lame. He has made up this mind & had the tanks installed, LPG is what he wants.!!

When you have more money than sense you will only take your own advise (or maybe some, so long as it is free & fits with what you have already decided).

 

[Scol]

The property is circa 3500 Square feet.

Lame Plumber, I think most people could work out how to steal oil but most would not have a clue with Gas but I agree that that anyone who is truly determined will find a way and they would probably steal your pellets too

Why are you so anti LPG, is it largely down to cost/sustainability?

Thanks for your help.

 

[IDCHAPPY]

I'd want to fit 2 boilers as well, saves horsing one to death and you have back up if one fails

 

[Scol]

Chris, bit harsh, I most certainly do not have more money than sense and have chosen an option that I believe best fits my complete circumstances (not all of which I am willing to share on a public forum).

I am very happy to take advice, in fact the advice that I have paid for is to fit a boiler that may be excessive for my needs hence seeking some friendly second opinions.

Thanks

 

[chris watkins]

Fair enough, but if you don't want to give the full story the people on hear can't help you & you will get a reaction like mine.

This design lark is not based of guesses we need hard facts.

I think you may have got an idea from the reaction so far that the advice you claim to have paid for is unsound. Take some freely offered, find a professional in whom you can trust, tell them your requirements & let them do there job, some of us are very good at what we do but do have the cheek to ask for a small payment for this service.

Good luck

 

[Ray Stafford]

Why are you so anti LPG, is it largely down to cost/sustainability?

Most installers in the UK would only use LPG for two reasons

1) For mobility - caravans, boats etc or
2) Because there is a reasonable hope of connection to mains gas in the near future - in which case it makes sense to put in LPG equipment which can easily be converted

Its more expensive than oil and obviously much more expensive than mains gas. It also has some unpleasant tricks up its sleeve, particularly if your property has a cellar.