heating / hot water - whole new system

[dptenancy]

good morning

i have just gutted a four bedroom townhouse over threes floors - ground / first and attic.

i have therefore to decide what heating / hot system i should put back in as there is nothing right now - not even a copper pipe!! there is mains gas and electric.

it is of 1950's construction, so the walls are not very well insulated - the roof is well insulated. i am thinking of a radiator system as i am on a limited budget and underfloor heating will be too expensive.

water wise - there are three showers (1 on each floor and it is likely that at least two will require water at the same time. there is also a bath on the first floor but unlikely to be used much.

there's plenty of space to mount pretty much any system but i really don't know what's best - probably most concern is the demand for hot water - a simple combi boiler could not handle it. and i only want one electric shower as an absolute emergency.

i should say that i don't expect to live in the property for more than 5 years at the most so i do not want to pay huge amounts for a renewable energy system that takes years and years to re-coup the investment.

any advice gratefully received. thanks

[News]

In message , [e-mail] writes

Doubtless you will receive plenty of conflicting advice, but, given that you have gas, I would go for a traditional gas boiler and showers fed via a large hot water cylinder with immersion heater for emergencies. Other will advise on calculation of boiler and tank sizes - take the advice and add 10 per cent.

Our system is oil fired but otherwise as above. Plenty of capacity for the traditional radiator central heating, plus hot water. The water is heated twice a day, for one hour early morning, and another hour mid afternoon. Two of us shower in the morning, and one in the evening. Very occasional baths. We never run out of hot water.

Two caveats. One, I'm biased and hate combis, and Two, although we have several showers in the house, for no particular reason, we rarely seem to run more than one simultaneously.

[Michael Chare]

Some thoughts:

If you have a conventional system with a hot water tank, then you can have an immersion heater for use if the boiler fails or you want to stop it for any reason.

OTOH If you have cold water tanks in the roof you need to ensure that the water does not freeze in the winter, especially if the house is left unoccupied.

Another issue is whether you have a system boiler. These are more complex, presumably cost more and are more tedious to fill. OTOH you have to install a header tank for a conventional system.

My fully pumped conventional system uses fully motorised valves which don't move if the programmer switches the heating off and on to achieve proportional control.

I am not a fan of thermostatic radiator valves. I would regard a wired in programmable thermostat as essential, preferably with remote control.

Many programmable thermostats are single channel. OK for the CH but I like to have the HW off when it is not required.

[Tim Watts]

First thing: do you have a cavity and is it insulated - if not, do that first.

Then big efficient radiators. Bigger than you think, subject to space.

Use the manufacturer tables to ascertain power output and then double the size over what it needs to maintain steady state (or what you think it needs).

For little extra cost (ordinary rads are not expensive), it will:

1) Keep the boiler happy avoiding cycling;

2) Give you a faster warm up from cold so less unnecessary heating;

3) Allow the heating to run at a lower water temperature which is more efficient on the boiler (upto a point) and more comfortable to humans (usually - opinions vary).

For example - a house I have with 2" cavity wall blown fibre (old) and

3" celotex in the roof requires a total of about 3-4kW electric heaters to maintain steady state 21C downstairs when outside is 5C ish.

However, it takes a day to 2 days to come up from stone cold with 4kW.

So I will be aiming to put in a total about 5 times that at least in terms of max output power of radiators at the usual delta-T, then I can drop the water temperature (and thus the delta-T) a bit too.

On the basis of what you've said if you have not got figures for how lossy your house it, then I would aim for 3-4kW for a massive room (ie really large lounge), 3-4kW for a large bedroom, 2-3kW for a medium bedroom and 1-2kW for a tiny bedroom and so on.

And zone it, at least by floor.

You'll save more in rapid warm up when needed, then being able to turn it off in unused areas when not than any amount of fancy wibbling with heat pumps, solar panels and the like will ever give you.

On the subject of insulation, if you have no cavity, do you have the space to put 1-2" celotex on the inside walls (at least external walls) then plasterboard? Even 1" over bare brick will make a very large difference to both comfort and heat loss.

Cheers,

Tim

[Roger Mills]

I would use a conventional boiler - not a combi - to heat both the radiators and a hot water cylinder. Install a *large* cylinder and insulate it well.

Zone the heating system - probably one zone per floor - making four zones in all including the hot water. [Depending on how the rooms are used, some different zoning scheme may be appropriate - living areas, sleeping areas, etc. regardless of floor.]

The primary system should be non-vented.

The DHW system could be vented - with with a large header tank in the attic, or you could use a non-vented mains pressure cylinder. Only use the latter if you if you've got *really* good mains pressure and flow - otherwise bath filling - and particularly showers - will be limited by what the mains can supply. I would tend to favour a vented (gravity) system with large diameter pipes from the cylinder to the principal usage points, and with booster pumps for the showers. [You'll need to feed cold water from the header tank to the showers as well as hot from the cylinder].

With a 3 storey house, you will inevitably have long pipe runs from the cylinder to some of the taps - possibly making some sort of constant circulation system worth considering so as to avoid having to waste a lot of water before any hot gets to the taps. Alternatively, for relatively low usage applications such as kitchen sinks, you might consider an electrically heated device (Quooker, etc.) which stores a few litres of boiling water in an insulated container under the sink and supplies virtually instant hot water to the taps.

[spuorgelgoog]

However, as combis are often cheaper than corresponding non-combi versions, you could use the combi hot water for one shower, or the kitchen tap, whic h will give you instant hot water in that location without waiting for the cylinder to heat.

If you're only going to be in the house for

[Fredxxx]

The consensus is a system boiler and I agree with this. Combis are great for small houses.

Oversize the radiators. The cooler the CH return temperature the more efficient the boiler can be.

One issue is that with a conventional CH/HW system with a diverter is the boiler outlet temperature is fixed, leading to a conflict on temperature required to heat HW and the lower temperature desired for CH. A heat store type arrangement might be more appropriate.

This is more of an issue. I would suggest at least one is electric. For two or more there is the issue of only having 100A incoming fuses. I understand there is no allowable diversity on two "water heaters", 50% allowed on further "water heating".

[Martin Bonner]

At this point, I would insulate the walls. If you have a cavity, get it filled. If not, consider whether you want to add external insulation or internal.

External:

• The walls act as a heat store, keeping it cool in summer and warm in winter.

• No loss of space inside

• No problem with interstitial condensation (because the thickness of the wall stays warm.

- May look naff outside, and particularly difficult if you are in a conservation area.

- Difficulty detailing at roof and windows.

Internal:

• Wall is outside the insulation, so house heats up quickly when you come in in the evening.

• External appearance unaltered

- Need to be careful about interstitial condensation. Need a really *complete* vapour barrier.

- Some loss of internal space.

When we insulated the inside of our bathroom with 100mm wood fibre (Pavadentro) it went from the coldest room in the house to the warmest.

Really? 200mm of glass fibre?

Sensible enough.

Sounds like you need a system boiler and a hot water tank or thermal store.

Think about siting the tank and plumbing so that you can fit solar thermal later, even if you don't fit it now.

A nice warm house that you can gloat about how little it costs to heat will sell much more readily when it comes time to sell. (You may not make the pound costs back, but the reduction in stress when it sells quickly has value - and you may make the money back too.)

[The Natural Philosopher]

No, they are crap even for small houses.

If they are big enough to deliver hot water for a shower, or have a heat bank, they are more expensive than a system boiler and a pressurised hot water tank.

A combi and a heat bank is like a windmill and a battery. Tow bad ideas bolted together to make a truly awful and expensive solution.

[Martin Bonner]

Rubbish. The combi in our three-bedroom house was fine. Two or three adults. It struggled if two people wanted a shower at the same time, but some people don't view that as the end of the world (others do of course).

[Graham.]

You just told us why. "Two of us shower in the morning".

[Fredxxx]

Agreed, though I might put the limit down to 2 bedrooms.

For a small house it can save a lot of room where tanks would be.

It's ideal for someone at work all day, where no water is stored so no heat loss; where the proximity of kitchen and bathroom often mean little water need be run until you get hot water.

No 22mm pipes taking to flush with hot water at low pressure before you get hot water out of a kitchen hot tap. Power shower without any further equipment, just a simple thermostatic mixing bar.

Some people are blinkered, and in denial, of the advantages.

[News]

In message , Graham. writes

But the two who shower in the morning may, or may not do so simultaneously.

[Michael Chare]

Other points I would add:

a) Use radiators with a rounded top rather than a welded seam.

b) Install a heated towel rail in the bathroom.

c) Install drain points in the pipework to each radiator that won't drain without one.

d) If you have a hot water tank, get one with 50mm insulation on it.

[Adrian Caspersz]

Rust?

Mine heat towels better than heating the room. Probably just me.

A new boiler will cost £4,500 + gas costs.

For mere amusement, over 5 years could it be cheaper on electric with ceiling fitted infra-red panels, room occupancy sensors and much better room insulation fitted?

[Michael Chare]

Why do you think rust would be a problem for round top radiators?

I presume your £4,500 is really the cost for all the CH parts!

[Adrian Caspersz]

What was your justification for the rounded top. Just interested, that's all. Guessing some issue with leaks or rust for a seam?

£1000 boiler cost, £2000 4 to 5 days of labour, £1500 other bits - all inc VAT.

[Michael Chare]

I just think they are nicer than those with welded seams at the top.

Labour! This is UK.d-i-y

[tabbypurr]

on a limited budget you could check out the boilers on ebay. Should save you most of a grand.

gas boiler & cylinder then. Again there are used cylinders around at times.

cheaper to add an immersion element

costlier to fix

TRVs are only semi thermostatic, not truly thermostatic. But it beats no thermostat on each rad. A separate real thermostat per room is certainly better, but if you'll be moving out I'm not sure the expense is warranted.

Bimetal stats are fine. Technology doesn't always produce a win.

pointless gimmicks imho. OTOH a future buyer might like it.

or place it where you can stick more than 2" of loft insulation round it.

NT

[www.GymRatZ.co.uk]

I've found in both the victorian flat over our shop and our 1960/70 detached house with non insulated floors, when using the "radiator sizing charts" they've always been wildly over sized. When I sized up the radiators for the bedrooms at home to work with UFH flow temp. I needed massive rads. So in the end based on previous experiences I simply took the biggest single panel finned radiator that would fit in the space where space wasn't a variable i.e. under windows (single so it didn't stick right out into the room) and used radiators that "looked" the right size in the hall and master bedroom.

All chuck out more than enough heat even with flow never exceeding 55 degrees MAX. to bring bedroom up to temp quickly.

Not a very scientific approach but one based on previous results of a "by the rule book" sizing.

Wouldn't an over-sized radiator system make the boiler cycle more than a system where the radiators are perfectly sized for all but the rare week or 2 every 10 years or more when temperatures go into minus double-digits?

Easier to add an additional heat source in those rare and exceptional conditions than to design a system with huge over-capacity that will rarely be required.

It's all energy consumed. Bring it up to temp really quick with a high input or slower with a lower input. A steadier and more constant lower heat input would be preferable from a comfort perspective. Weather compensated Boiler keeps temp nice all the time. With UFH it means the floor is always just right. If I push 55 degrees around all the time, the floor goes off and cools rapidly (between joists so no thermal mass) which means a floor that's cold long before the room stat has dropped to it's low set-point to fire up the zone and re-heat the floor.

Definitely. And weather compensation is an absolute must-have for both economy and comfort. :)

When would you ever need to heat from stone-cold? I'd always leave the heating set to perhaps 15 degrees if I could be arsed to re-program all the room stats which I wouldn't. :)