Heating/HW in a new-build granny flat?

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One possible solution would be to fit a single conventional radiator piped from the nearest existing pipe run.

A gas multipoint water heater (totally independent of the main system) could be used for constant hot water. If space is at a premium some multipoints can be fitted outside which might be worth considering if there's sufficient dead space outside.

Cic.

Electric anything is expensive to run compared to gas. If you do go for radiators (or part radiators) consider safe-to-touch ones that have a lower surface temperature.

If it's a really small space and very well insulated then an electric boiler (eg Dimplex Ascari) might be a way round it, you are still paying for peak rate electricity but you get the benefits of 'conventional' heating.

Older people often like a "fire" to sit in front of so swallow any taste objection to electric logs and get a built-in flame effect fire with a fan heater.

What hospitals etc do is have a loop of hot water pipe and a circulating pump, this means the water in the pipes is kept hot (no legionnaire's) and use thermostatic mixing valves at the outlets.

Instant electric showers, I find, aren't particularly controllable or stable in temperature. Local stored hot water would probably be best; can be heated from an extra loop off the main boiler or electric immersion (or both). Pump if necessary and use thermostatic valve.

Stored hot water cylinders can be squeezed into places - what about under the worktop in the kitchen corner unit - older person probably not going to want to faff around with a carousel or similar to get stuff from the back, so it would otherwise be wasted space.

Stick the wires in for emergency lighting and emergency call buttons during building.

Owain

Owain

It is.

It isn't a good idea because it isn't well suited to underfloor, hot spots can develop and reliability traditionally has been poor. Wet is better.

Yes, we have has a whole house full of it and carpets for 15+ years.

He must have meant to say 4 or 5 metres square, rather than 4 square metres, which would be slightly larger than the average porch.

Yes, but don't do direct electric if you can avoid it. Go heat pump. Or tap off the main boiler and run your UFH of that. You need a separate zone for UFH anyway, and a pump so its no big deal, you can have a separate controller. My advice from experience here is don't time it, especially with 24x7 occupancy. Just have a thermostat that the invalid can turn up or not, and leave it on all the time. Mine's on that way now, but since its warm enough, it never comes on..

Oil or gas is about 4p a unit equivalent, so electricity is likely to be twce as expensive to run. If you are constructing from new use wet pipes in the floors. The incrementall cost of a small annex is probably

You answer here is simple: hot water, especially for an elderly person who probably won't use much is a separate immersion heater, my choice would be mains pressure, because its the smallest foot print. You cant have an electric combi style thing that can produce enough power to heat on the fly, so storage is indicated. Its not worth running pipes if instant hot water is what you want. And unless you have mains pressure tanks already, flow is likely to be affected by the pipe runs.

OK, my instant reaction is this.

Its a new build, so modern insulation will apply, and that makes it suitable for UFH, although wall to wall carpeting will reduce the efficiency of this and you will need extra insulation underneath, and a LOT of pipe in the screed - I assume this is a ground floor only setup?

What I used here would work for you.

Hot water ========= Old people dont lie in baths all day, nor play with themselves in the shower, nor do they do a lot of washing or washing up. So you probably could get by with as little as a 100 liter tank, with an immersion heater. If you use a mains pressure tank, all you need to run is a 22mm cold mains feed, which you take to the cold taps, and feed to the tank, which is probably about the size of an undercounter fridge, and can be tucked in the loft, or anywhere convenient, and a 3KW spur off a ring main (or a separate 16A spur from a dedicated MCB in the consumer unit).

Pipe that to the hot taps and that's it. Job done. A tank like that is about 400-600, plus fitting.

UFH ====

What you need here, is to plan for at least 4" of insulation and 4" of screed full of plastic pipes..with hindsight, cram those in in a coiled spiral at 4" spacing or so, to get maximum heat transfer to the floor from the hot water, with no pipe run being more than 100meters in length. Tale those to a manifold that has the option of zone control valves. You may not need them, but its nice to have separate control for bedrooms and kitchens if he complains its too hot etc etc. Consider a hot towel rail as well in the bathroom.

On MOST setups you will need an auxiliary circulation pump and a temperature reducing valve on this. Plus a motorised valve for the whole UFH, and a thermostat and if you think you might need it, lay in cables for thermostats in the kitchen and the bedroom as well, since these are the areas you are likely to want to run cooler than the living area. Which will be your master thermostat. You strictly should run an extension of whatever spur is used to run teh boiler, so that when the boiler is isolated electrically, so its this lot.

You will also need a mains relay, so that when you call for heat on the main CH it doesn't start the auxiliary pump going.

Wiring wise, you take the switched 'central heating' live via the main thermostat, then to the motorised valve and, via its contacts to the pump and the relay coil in parallel. The relay contacts go between 'central heating live' and the actual boiler.

So call for heat opens the motorised valve, starts the auxiliary pump, and closes the relay that fires the boiler and main CH pump.

All you need pipe wise is probably a 22mm flow and return coupled into the CH circuit of the boiler. The long runs aren't an issue here, as its both pump driven, and UFH tends to be 'flat out' heating for several hours to get the floor up to temp, and then several hours cooling down till the stat cuts in. A minutes delay isn't worth bothering about..

If you need auxiliary thermostats, my system at least allows electrically operated valves that cut flow on some of the UFH circuits: these are simply fed via the room stats from the switched live circuit.

If you need towel rails, its probably simplest to use electric ones, as the temperature and timing is likely to be different from the UFH.

After using such a system here, I would definitely recommend it for an elderly invalid. The heating is very mellow and constant, and the long time constants makes it ideal for 24x7 occupancy. There is nothing to fiddle with, except the main stat. (*unless you put in room stats)..you balance the zones on the manifold..

As far as heating power goes, again given that its 24x7 heating, you will find that the boiler tends to cut in about 4-5pm in wintertime, stay on for an hour or so, and cut out, and then come on again about midnight, and cycle through the night..this can be annoying if as we do, you sleep over it, but its not that big a deal. And in summer, a massive concrete floor INSIDE the thermal insulation will help keep temperatures down to moderate by day, especially if you draw the blinds to keep sunlight out, and SHUT the windows to keep the hotter air outside.

Open them at night when ambient falls below the internal temps. Old people can suffer from excessive summer heat, so this is all A Good Thing.

For a granny flat which is occupied most of the time, I would agree. Another factor is no radiators to burn the occupant. It doesn't suit occasional or unpredictable occupancy due to latency.

If you do go the radiator route, you might think about specifying oversized low temp radiators and heating circuit to reduce chance of a burn to the elderly. I know a case of an elderly person who fell asleep against a radiator, and did get a burn, and any burn is much more serious for the elderly.

Thanks very much for the advice - all good stuff and very helpful.

Looks to me as if wet UFH is the way forward if possible, but that would need taking off the CH system for the main house - see previous query, which may be a big issue!!

The point is that depending on occupancy of this annex, the heating needs to be totally independent; eg to be blunt about it, if my Dad moves in when it's ready, but later dies while Mum is still very active and still has the run of the main house, then the annex would probably be mothballed until such time as my Mum might need it - at which point the main house would probably be pretty much mothballed. Christ, I don't want to get old.

Am interested in the suggestion of a multipoint water heater. Am I right in thinking that these are essentially like a combi but for DHW only? Do they typically/always *include* an HW tank? (Is that necessary?) Are they a reasonable solution for a shower?

I anticipate that shortly I'll be having a meeting with the builder/heating engineer on the project and no doubt they will have their own ideas on the best way forward, so I'm keen to educate myself on all the possibilities first.

Thanks David

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Much less complex than a combi (HW only) and rarely if ever have a storage tank of any kind. Cold water (mains) is piped in at one side and delivered directly to hot taps / shower etc. from the other side.

They won't give you a power shower but they're usually very adequate for a normal shower provided that you want to get washed rather than washed away. In extreme mid Winter temperatures they might struggle to reach more than tepid but such occasions are rare. Can be fitted with a thermostatic valve, I think.

Try googling for 'Main' (balanced flue / no electricity) and 'Rinnai' (electric fan assisted ).

Cic.

Well that happened rather faster than expected; the plumber has just been round to my mum's and I've spoken to him by phone.

His verdict is that the main house system is too antiquated to add on to. Although the boiler is only about 5 years old, the rest of the system (1-pipe, vented, trouble-free) dates back to 1966 and as the plumber puts it, came out of the ark; he wouldn't want to touch it and would insist on re-piping the whole house if we were to add the annex on to the current boiler, which is a non-starter as far as we are concerned. I think I accept this decision but can't help thinking it may be a bit of an arse-covering exercise? Does it sound reasonable?

So his solution is therefore to fit a gas combi to the annex, which will therefore be entirely separate from the house. Heating will be wet UFH.

If it has to be a standalone system I can't fault the combi logic: my only concern about that really is potential noise from the boiler (being in the bedroom) but he assures me it will be completely silent. Is that realistic? (thinking of the heating coming on in early morning). Plumber's proposing to fit a Worcester-Bosch 30 cdi.

Thanks David

We have a Vaillant ecoTEC+ combi boiler in a bathroom cupboard, it's extremely quiet especially as it has been range rated so it doesn't have to fire at a higher rate than it actually needs to. IMHO Vaillant boilers build quality is better than a Worcester, I also find Worcesters to be very overrated.

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I think you're being railroaded.

Given that the existing system is working the addition of an extra radiator is unlikely to break it, particularly if you can sacrifice a radiator in the main building. I would want to know why your builder is so keen on UFH - maybe creating a job to keep him occupied. A multipoint can be fitted in a couple of hours or less and it's virtually maintenance-free. Time for a second opinion before costs escalate.

Cic.

Reasonable choice for a single person flat, where its unlikely a shower will be needed. and it does as you say excuse him from getting involved in legacy plumbing, which allows him to be predictable.

If you read my previous post, I reckon that a UFH should run 24x7, with the unit cycling mostly through the wee small hours when its coldest. If you time it, you probably need it on at least three hours before getting up.

The reason he won't touch the old system is not that it won't work - he will have been in a situation where such work has been done, a week later a leak develops in the old system, the customer says "it must be something you did, come and fix it". This was the (at least honest) reason my kitchen fitter gave for not moving a radiator (I did it). You may not be like that, but he doesn't know that.

A combi boiler may be quiet but one that is completely silent isn't working!

OTOH there are maintenance advantages in separating the systems and there's nothing wrong with his solution.

I've found running it all the time at one temperature not to be particularly good. The temperature in the small hours is too high for comfort. A better solution is something like the Honeywell CH907 programmable thermostat which allows you to back off the temperature at night and works out for itself when it needs to turn things back on.

That's why you run the bedrooms a couple of degrees coller.

A better solution is something like the Honeywell CH907

It takes my system about 3 hours to gain or lose a degree.

Timing is a waste of time.

Bit difficult when the doors are all usually open. Each room has its own thermostat and control valve but they don't make a vast difference.

In terms of boiler on time the heating comes on at about 06:00 for an hour or so and again at about 15:00 to get up to temperature by 19:00, it goes off at about 19:00 as well and then the temperature drops a degree or two by 23:00 and a couple more by 02:00.

Obviously the profile would depend very much upon the insulation and size of the Annex. The OP could go for your always on solution initially and add a programmable thermostat later if desired - just make sure the electrician puts a cable pair for it behind a blanking plate somewhere central and running to the boiler position.