Extension - seconded zoned gas boiler

[Diggory]

Hi forum; grateful of a steer on my options here.

Situation is that I’m adding a single story extension (50m^2) to a fairly old bungalow. The extension will be double glazed on two sides and have a vaulted ceiling. Its a ‘modern build’ so I’m hoping despite the ceiling and large glass area, not too bad to heat. My current boiler works absolutely fine but wont have the spare capacity; its a Potterton 60E running a vented system of 9 rad and the hot water supply. I’ve stocked up on boiler spares for all the bits that usually go wrong; so I’d like to keep it if possible.

I’m wondering could I add another, low capacity (gas) boiler zoned for just the heating of the 50m^2 extension. I’ve read about electric boilers but up to x4 the running cost puts me off. I’ve read about ground heat pumps but just cant get past the start-up costs (and maybe the cost of electricity to run one is x2 gas).

So I keep coming back to gas and wondering about the best option.
Should I go for a smaller gas boiler, zoned for the extension; with maybe underfloor heating. Or do I just put in a single bigger one and a couple of new / large rads.

Thanks in advance D

 

[D_Hailsham]

Whoever designed your extension should have done a heat loss calculation for the original house and the house with extension. Do you have this information?

 

[Diggory]

Thanks Reply.
No, I’m afraid I don’t yet have that info just yet. I haven’t progressed the design to that point / level of detail. It’s early days but I’d still like to understand the option space.

Best D

 

[sxturbo]

How many rads are you thinking of adding? Or under floor heating?

The potterton is an 18kw boiler, I think it will most likely be able to cope with the additions, but a proper heat loss calculation should be carried out.

Also it would actually be cheaper to have your existing boiler changed than to install a small secondary one

 

[Diggory]

I was thinking one large rad or two smaller ones but I haven’t ruled out an under floor system if that would help.

(I thought the 60E was 15kw ?)

D

 

[Mottie]

I was thinking one large rad or two smaller ones but I haven’t ruled out an under floor system if that would help.

(I thought the 60E was 15kw ?)

D

The profile 60e is definitely 18Kw (17.58 actually) and when we had ours, it would run 10 rads and hot water comfortably in the coldest weather on only 3/4 power. 11 rads would be no problem.

 

[Diggory]

Thank you - that’s good to know that I have some spare capacity.

As a matter of interest, is the second zoned boiler and under floor option just too complicated to be worth the trouble and bother.

Best D

 

[sxturbo]

Thank you - that’s good to know that I have some spare capacity.

As a matter of interest, is the second zoned boiler and under floor option just too complicated to be worth the trouble and bother.

Best D

The 2.nd zoned boiler yes.

Underfloor heating, expensive, but depends on the look your going for, kif you don't mind staring at radiators then is it a cost worth paying.

 

[sxturbo]

I have 11 rads and an 18kw boiler, no problems.

From memory my 1970's insulated 4 bed extended semi required a 16kw boiler when the heat calcs were done.

 

[Diggory]

Thank you all.
That’s been helpful.
D.

 

[Mr Chibs]

I’ve no science to back it up, but wet ufh seems efficient to me, as you run it low and long.
Mine is hardly on, once you’ve got the slab warm, keeps the room warm all day.

Also there wasn’t any massive rise in running cost. 30sqm, vaulted ceiling.

 

[vulcancontinental]

One boiler will be fine. Use Heat Engineer software for a complete heat loss of the property (2 hours and £10 for a one off or free for a less accurate heat loss). Underfloor is apparently great for a vaulted ceiling as it's the lower 2m that is kept warm. If you have 200mm of insulation in the loft of the existing bungalow, double glazing I'd be surprised if your heat loss was over 10kW

 

[cdbe]

There are simple things you can do if it's marginal - heat the hot water outside the heating times, put the heating on an hour earlier, get a gas fire in your lounge. We have a 15kw boiler, 4 bed semi with 45m extension in progress - I've discounted ufh due to cost and complexity and gone for "designer" rads instead.

 

[Diggory]

Thank you all for your advice; it’s been very helpful.
I’ve had an attempt at estimating the spare capacity of 60E at 17.58kw.

• 1x Double 60h x 16w / no fins 1,750 Watts
• 1x Double 60h x 95w / no fins 1,050 Watts
• 1x Single 60h x 175w / no fins 1,470 Watts
• 1x Single 60h x 80w / no fins 735 Watts
• 1x Single 60h x 110w / no fins 980 Watts
• 1x Double 70h x 60w / double fins 1,340 Watts
• 1x Double 30h x 145w / double fins 1,900 Watts
• 2x Double 30h x 145w / double fins 3,800 Watts
• Water Cylinder 3,000 Watts
• Total 16,025 Watts

If I’ve estimated correctly, I’ve got maybe 1,500 Watts of unused capacity.
For a 7m x 7m and vaulted ceiling, I was thinking I’d need nearer to 10kw.
Would this take me beyond marginal ?

best D

 

[vulcancontinental]

Thank you all for your advice; it’s been very helpful.
I’ve had an attempt at estimating the spare capacity of 60E at 17.58kw.

• 1x Double 60h x 16w / no fins 1,750 Watts
• 1x Double 60h x 95w / no fins 1,050 Watts
• 1x Single 60h x 175w / no fins 1,470 Watts
• 1x Single 60h x 80w / no fins 735 Watts
• 1x Single 60h x 110w / no fins 980 Watts
• 1x Double 70h x 60w / double fins 1,340 Watts
• 1x Double 30h x 145w / double fins 1,900 Watts
• 2x Double 30h x 145w / double fins 3,800 Watts
• Water Cylinder 3,000 Watts
• Total 16,025 Watts

If I’ve estimated correctly, I’ve got maybe 1,500 Watts of unused capacity.
For a 7m x 7m and vaulted ceiling, I was thinking I’d need nearer to 10kw.
Would this take me beyond marginal ?

best D

You're looking at it in reverse. You have the output of the radiators which are normally oversized. As an occupant you wouldn't know this as you'll always be warm, you notice very quickly if they're undersized. Do a heat loss then you know what the load will be not what the radiator outputs are.