Gas boiler for central heating, electric shower and taps?

[318Mike]

Present.
Hot water and central heating is by BAXI back boiler in the lounge.

Proposed.
Gas fired central heating boiler installed in the garage. Gas and electricity meters are in the garage, water supply is adjacent.
Electric heated tap to supply hot water to kitchen. Shower heater installed in loft to supply bathroom sink and shower.

Advice please.
Is this set-up doable?
Has anyone done it?

Experience.
I have replaced all the radiators, valves and some kitchen piping. Abroad I have installed butane gas boilers and electric water heaters.
I have used remote shower heaters and heated taps in Europe and appreciated the instant availability of hot water.

Thanks in advance.

 

[Wayners]

Putting water heater in a loft with the extreme heat in summer and freezing cold in winter plus not being able to monitor it is not the best location.
Boiler in garage can be ok though.

 

[ericmark]

I question why not have the gas boiler heat the DHW? Not saying wrong, I have considered some thing similar myself. Depending on how much DHW is used, electric can be cheaper for small amount, as no delay heating the pipes. But in my case 5 locations for DHW, so would be a lot of work moving to local electric heaters. So I still use electric during the summer, as an immersion heater in the cylinder. My oil boiler only heats DHW when the CH is running.

Seen many under sink heaters, often around 5 litres of water heated, not seen one which can work shower and sink, the consideration is the electric load. My house has a 60 amp DNO fuse, and in general want to keep loads to under 3 kW as that is max output of battery at the moment, want to fit a second one so then 5 kW (max for inverter) but to use off peak or solar, have to consider load.

I in hind sight made a mistake, I fitted an iboost+ to immersion heater, in general off peak 9p per kWh, export 12p per kWh, peak 31p per kWh so cheapest time to heat DHW is when getting off peak. So where you can you want enough store of DHW to be able to use in the main just the off peak electric to heat.

As it stands still getting no payment for export, so the iboost+ is still the best option, but not really practical to have multi iboost+ installed. What I do want is a longer immersion heater so more hot water stored.

In a caravan I used an under sink 7 litre water heater with the 3 kW element swapped for a 1 kW element, and it worked fine, never run out of hot water, the down side is cupboard space lost under the sink.

I was surprised to find my instant electric shower only uses 6 kW, seems two elements in the shower so option of one or two elements but we have only used the single element, which is seems with the solar software monitoring the power use, is only 6 kW and has proved ample. Just as well as we have two instant electric showers, so if larger could rupture the 60 amp DNO fuse.

Yes large house, two kitchens, three bathrooms, five bedrooms, so you may not have as much demand on electric to me, but still needs considering.

 

[cdbe]

Unless you live in a mansion a centrally located hot water cylinder with radial pipes will supply hot water to each outlet within seconds.

 

[ericmark]

Unless you live in a mansion a centrally located hot water cylinder with radial pipes will supply hot water to each outlet within seconds.

Really! I would not call my house a mansion, big yes, mansion no, the problem is pipe size, with old houses, 22mm, and 32 mm pipes are common, often with no lagging, these radiate the heat, and in winter that is not a problem, want to heat home, but summer it can mean more heat is lost than is stored in the cylinder.

My front kitchen I get nearly a bowl full of water before the hot arrives, and mothers house with a combi boiler DHW would start cold, go hot, then cold again, and finally hot for the shower as the reservoir of hot water in the boiler was depleted and then the boiler finally caught up. Which gives on an idea of how much it takes to heat the boiler, at work referred to as cost of a match, the cost to get boiler to temperature before it does any work. OK the boilers are bigger but same applies, cost to get boiler to temperature, so how much DHW is used per day matters.

One thing my iboost+ does is record how much power used per day/week etc. It has been an eye opener, seeing figures between 2 and 3 kWh per week, but oil boiler which does not modulate would run 4 times a week for approx 20 minutes a time, so more like 25 kWh per week, so to heat boiler and pipe work between boiler and cylinder needs something like 20 kWh per week, that's not counting losses cylinder to tap.

So to my mind @318Mike idea is good, local DHW heating can save money, but at an average of 2.5 kWh per week, which using off peak will cost around 25p per week, is it really worth replacing the immersion heater with multi electric heating devices? My cylinder only has the basic sprayed on insulation, plus airing cupboard full of clothes, so money wise not worth multi DHW heating units.

The same applies to changing out instant electric shower, for a thermostatic controlled shower off the DHW, the latter is better, but former adequate, and the latter uses more water, plus my wife spends same time under an electric instant as she did under the thermostatic controlled one in last house, if anything she was in shower longer in last house as she waited for the shower temp to stabilise.