What plumbing/cabling/preparation is needed to prepare for ASHP in the future?

bobfredbob

We want to replace the carpet, which means I'm now wondering what disruption an ASHP would cause at some point in the future (assuming everyone will eventually have to have one or a hybrid system) to decide if there is anything we can do in advance.  We had a lot of disruption moving to a condensing boiler.

We have a mid-terrace, with a suspended floor, a gas system boiler at the rear with a separate timer, fuse box/gas meter at the front of the house, thermostat in the living room, control wiring and vented cylinder in the middle upstairs.

Is there anything that goes inside the house such as expansion vessel, filters, control boxes, etc?

I read that many heat pumps have an immersion feature, so I assume they need a separate 3kw(?) wiring from the fuse box to heat the water at the heat pump.  Or do they communicate to the existing hot water immersion?

I believe the outside unit needs some drainage and can't just drain on to slabs?  Is this a permanently fitted pipe similar to the condensate pipe in sizing?

The pump would then only need flow/return pipes, either hooking in where the boiler is, or some path to my 3-way valve next to the cylinder (which would become hot water priority valve).

In summer is the unit off (while no hot water needed), or does the unit always make noise (albeit low noise)?

At what time of day would it be cheapest to heat the hot water cylinder, i.e., during daytime temperatures or nighttime temperatures?

Can the units be wall mounted, or are they all floor mounted and need concrete underneath?  I assume no-one would service/install it wall mounted above a flat roof. 

The government had a consultation about removing the 1m minimum distance to neighbours and the maximum size a unit can be.  Any ideas if this will go ahead or when?

Would waiting for larger sized units have any benefit, such as performance, quietness, cost, etc?  Are any such units known?

When do the current rebates/discount offers end?

If the gas meter pipe is capped off/removed, would the pipe be capped off underneath the floorboards (where it enters the house) or would I be left with a pipe sticking up in my cupboard?

Lots of questions since it's very difficult to find the answers.

Thanks for any answers.

FreeBear

bobfredbob said: Is there anything that goes inside the house such as expansion vessel, filters, control boxes, etc?
When do the current rebates/discount offers end?

Funding under the Boiler Upgrade Scheme will continue until the end of March 2028. It might be extended further, or it may be dropped completely depending on the whims of the government.

As for the equipment installed - The existing vented DHW tank would be replaced with a sealed one running at mains water pressure. You'll probably need a second tank as a buffer (these can be quite small at 50l). You would need a 3Kw feed for the immersion heater, but you'll probably have one in place already.

I replaced my heating system last year. Fitted bigger feed/return pipes (22mm) and used 15mm for the final connection to the radiators. Oversized the radiators by 30-50% where possible, although most of these would need to be even bigger with a heat pump. Insulating the heck out of everything and killing all the cold draughts - Combined, this work will put me in a better position when I eventually have to switch to a heat pump. Have a spot earmarked for DHW & buffer tanks, and will put pipes & cables in at some stage in preparation (need to pul kitchen cabinets out to do that..).

In a typical terrace house, you'd probably only need a 5KW unit, so fairly small & compact.

Netexporter

As it is a terraced house I think the first priority is to check that you'll be able to fit an ASHP within the planning guidelines. It could fall at the first fence if there is nowhere suitable to site the outdoor unit. There are some relaxations coming, I understand, so bear that in mind. You may not be able to fit one today but that may change when the new regulations are enacted.

DougMLancs

A few answers based on what I’ve learned the last year of having one.

Many newer ASHP now use a propane refrigerant (R290) which is more effective at reaching higher temperatures and so although you may well have a backup immersion, you’ll likely never use it as we’ve found its between 2.8 (60 C) and 4 times (48C) more efficient to let the heat pump do the work. In the summer, the unit will only run when it’s doing a DHW run. For when to heat your water it’ll depend which tariff you choose but it can be whenever you’ve got cheap electricity available, in the winter you may want to do it during the day so that the heat pump can concentrate on heating overnight.

Many installers are moving away from buffer tanks as they’re a drag on efficiency. Instead they maintain the minimum required water volume with a no-zoning ‘open loop’ approach. 

It depends on your plumbing but a well-designed system shouldn’t need mass pipework upgrades, we’ve got 22mm primaries and 10mm drops to the radiators and it works fine.

Have you got all K2 rads at the moment (double panel, double fin)? This was all we needed to upgrade in order to run a 35 C flow temp.

Anecdotally, I’ve heard a lot of solid wall houses can have great performance (as long as draughts are tackled. You do need to keep the system on (though it won’t necessarily be running) 24hrs with any type of property since as you say, the initial warm up will take a while. This seems counterintuitive when you’re trying to reduce energy but it’s more efficient for the heat pump to sip 400W (or whatever) to maintain the temp (nighttime setbacks of a few degrees are fine) than let it drop dramatically. 

For noise, not all manufacturers create their units equal (Daikin are harder to meet the MCS noise calcs than others) but most are putting a lot of effort into sound dampening. Even in winter, you wouldn’t guess ours was on until you were within a metre or so. 

In terms of gas supply, initially ours has been capped off above ground level. We’re due for disconnecting from the street supply soon but I don’t think you can touch that pipe even after that.

bobfredbob

Thanks.  Yes, I had over-sized double panel/double fin installed a decade ago (to much laughter by the plumber), and external insulation, and new windows.  Just need to consider some type of ground floor insulation and a new front door.

I'd not heard of R290, which can apparently heat to 75C.  I imagine the promotion heat pumps (Octopus, etc.) are an older variety, but I would have to look in to it.  Though one manufacturer warned that the problem with R290 is that people then won't insulate their properties and so incur higher costs.

I'd not heard of the buffer tank either so it's good to know I might need space for that, but maybe not.

At the moment, I could only get the pump fitted at the front due to lack of wall space at the rear since there's a conservatory with full height glass, but a rule change would make the rear viable and would allow it to sit exactly where the (very) old non-condensing boiler outlet used to sit at ground level.

If the immersion/anti-legionella is only at the tank (not at the heat pump itself) then perhaps I don't need a dedicated power cable from the fuse box to the heat pump and it could possibly just reuse the boiler's fused spur.

An unvented cylinder will need some consideration since we have an old mains pipe and will need the upstairs floorboards lifted to route the new cylinder's overflow, so it's good to know now before we do the upstairs.  We'll have another think about if the tank can be relocated before we do downstairs in order to get a straight modern mains run.

So, it seems, if the installation rules changed, then it wouldn't require major disruption in the living room, just some upheaval upstairs with the tank, and the routing of kitchen boiler pipework outside at ground level.

Reed_Richards

My 12 kW heat pump is on a dedicated spur with a 40 A rated circuit breaker.  You may not need such a powerful heat pump so you may not need a 40 A circuit.  But a gas boiler doesn't draw much electrical power so it's very unlikely that the spur it uses now would have enough current-carrying capacity (i.e. thick enough wire) for a heat pump.

bobfredbob

Thanks for the info on the amps.  I've no idea the actual kw I would need, but you're right, even at 5kw it would require 5000w/240v=21amps, so I imagine a minimum 32amp dedicated wire would be put in.

I'll have to check the fusebox rating since we have a 9.5kw electric shower and I remember we couldn't (easily) have two electric showers fitted to be on at the same time.

So would this mean losing the electric shower if we have a heat pump?  The unvented will give a better shower than electric, and I guess the immersion is good enough as a backup.

Out of curiosity, how do people with concrete floors/mid-terrace do these type of new cable runs?

DougMLancs

bobfredbob said:

Thanks.  Yes, I had over-sized double panel/double fin installed a decade ago (to much laughter by the plumber), and external insulation, and new windows.  Just need to consider some type of ground floor insulation and a new front door.

I'd not heard of R290, which can apparently heat to 75C.  I imagine the promotion heat pumps (Octopus, etc.) are an older variety, but I would have to look in to it.  Though one manufacturer warned that the problem with R290 is that people then won't insulate their properties and so incur higher costs.

Octopus’ new heat pump they developed with Alpha that they’re rolling out is R290, I’m not sure what British Gas are fitting but I do know their new head of heat pump design is a perfectionist (he designed ours before he joined them and he has no filter when discussing bad design!) but I dare say that hasn’t trickled down to their installers just yet. I’m not sure I could stomach being involved with BG personally though.
For DHW, the R290 will just mean that you can do the sterilisation cycle nice and cheaply and then it can be set to a lower temp the rest of the time. 

For heating, you’re right, it does allow Octopus to take the fabric fifth approach to minimise upfront costs (a major barrier for stress purchases) but I believe they still use 55 C flow as a max design temp. It’s surprising what can be achieved with a few rad upgrades though, we’re a 60’s semi, only have 270mm loft insulation, 25 yr old DG, 15 yr old fluff in the cavities and an uninsulated concrete floor and we can run a 35 C flow. My brother in law has an old Edwardian end terrace and they run a 42 C flow (they have done some IWI and put in MVHR mind you). Essentially you can do the low hanging fruit of insulation (loft, replace SG door/windows, draughts) but expensive upgrades like internal/external wall insulation can be worked around if funds aren’t permitting and still maintain comparable running costs to gas with a well-designed system.
Ours cost £1 a day on average in winter for heating and DHW.

saveallmymoney

bobfredbob said:

Thanks for the info on the amps.  I've no idea the actual kw I would need, but you're right, even at 5kw it would require 5000w/240v=21amps, so I imagine a minimum 32amp dedicated wire would be put in.

I'll have to check the fusebox rating since we have a 9.5kw electric shower and I remember we couldn't (easily) have two electric showers fitted to be on at the same time.

So would this mean losing the electric shower if we have a heat pump?  The unvented will give a better shower than electric, and I guess the immersion is good enough as a backup.

Out of curiosity, how do people with concrete floors/mid-terrace do these type of new cable runs?

5KW is the output, not the input. My 7kw Daikin says it should be on a 19+ amp circuit, but the max draw is only about 9 amps.

However if your unit has a backup electric heater, that can increase the required circuit size considerably.

bobfredbob

I was thinking this morning about heating hot water and the controls with the R290 pumps.  Since it can reach 75C it can heat the water far quicker than the 55C pumps, but it would presumably cost more due to lower efficiency.  So, ideally I'd need the controller to have a separate max flow temperature for hot water and heating (which I assume would already be on some weather-comp style heat curve) since it doesn't matter if it takes two hours overnight.

I guess a very smart controller could be adaptive and only flow at tank temperature +5C so we would have the maximum COP for the longest, at the expense of a slow reheat time.

I looked at a few different heat pumps.   As you say, several up to 7kw needed to be protected by a 16a fuse, or 25 amp for higher wattages.  Interestingly, the Intergas Xtend (5kw hybrid) suggested 7.8a if I read the manual correctly.  Perhaps it's because the Intergas is only a 55C pump that doesn't do hot water?

It also seems many modern immersions are 6kw (my existing one is 3kw) so, ideally, I'd need a new wire for that.

I also liked the idea of the Vaillant uniTower, basically a hot water cylinder hidden in a box to look like a fridge freezer, so it could be hidden in the kitchen, but it seems it needs 30cm clearances either side if I read it correctly.

DougMLancs

You’ll find the controller does a lot of this for you. Ours is set to kick in when the tank temp drops more than 5 C below the set temperature (47 C) and this uses about 0.7kW a day at the moment (0.9kWh on one of our coldest winter days last year (see pics). Legionella cycle timed for Monday afternoon (when there’s usually plenty of solar) and that uses around 2.2kWh to take a 180L tank to 60C. Ours doesn’t have a backup immersion installed at all. 

We went for an integrated cylinder with our Panasonic as it was going in the kitchen where the combi used to be. Looks smart although what they don’t show in brochures is that you still need somewhere for the expansion vessel so built a cupboard above it to hide those bits (also handy for washing powder and other things we want to keep out of reach of little hands!). I hadn’t quite finished it in these pics but you get the idea. Ended up putting a single unit MVHR fan where the boiler flue was. The installers noted a similar statement about clearances on our indoor unit but after discussions with Panasonic, there turned out to be no real reason to maintain clearances providing there’s enough room to initially fit the unit in place.

In terms of manufacturers, you’ll probably find each installer has their own preferred option. I would steer clear of hybrids however, partly because they don’t qualify for the grant but also I would say an installer who suggests a hybrid doesn’t trust/understand the technology and I would look elsewhere.