Water flow 12L/min: too low for an ASHP?

Wiltshire_Dog_Dad

Hi Everyone!

I currently have an oil boiler and want to take advantage of the current £9k govt grant to change to an ASHP. Quote from Octopus seems great value at just £2.5k above that, which also includes 1 additional radiator and a 150L water cylinder.

The only fly in the ointment is that they measured a cold water flow of 12L/min in our downstairs bathroom sink (the closest one to where the heat pump and water cylinder would go… and we think also our fastest tap!) but they said they will need 14L/min in order to install an ASHP.

Has anyone else been told their flow rate is too low? Is this something I can reasonably ask my water supplier to increase? Or is there anything else that we could do to improve it? Seems like we are so close to being eligible for the heat pump but not quite there!

Thanks in advance for any advice or experience you can share with me.

Netexporter

I've not heard of this before and I'm struggling with why it matters. It will take slightly longer to fill the system but you only do that once.

Have you checked that both your house stopcock and the one in the road are both fully open?

QrizB

Is your current system an open vented one, with a storage tank in the loft?

Octopus (like most ASHP installers) will be fitting a mains pressure system. No more storage tank, no more legionella risk, but the max flow rate from your taps will be limited to how much water the mains can supply.

12 litres per minute isn't exactly low, but it'll limit how fast you can fill a bath and/or how "watery" a shower you can have.

(We've got an open vented system at the moment, and we can fill a bath faster than the loft tank can refill. This isn't a problem because the loft tank holds more water than our bath does, so it never runs dry and will refill before anyone's ready for a second bath.)

Netexporter

<slaps head>

So more a matter of convenience. I'd have thought the extra pressure would outweigh the lower flow in a shower, unless the shower head is one of those dustbin lid sized jobs.

I wonder if there is anything in the water regulations that specify minimum pressure/flow at the stopcock that suppliers must meet?

Reed_Richards

I looked this up and there us something called an Accumulator Tank that you can use to boost your water pressure and the flow from your taps.

FreeBear

Round here, 10l/min is regarded as good (I usually get 9.6l/min). Should not be a barrier to installing a heat pump, and I would challenge any installer if they use it as an excuse.

Whilst 10l/min isn't brilliant for hot water delivery, it shouldn't affect the performance of a heat pump in my opinion.

Netexporter

IIRC the flow restrictors that water companies give out to regulate your shower are 12l/m.

Wiltshire_Dog_Dad

Thank you all so much for your replies and information! Our current system is an old oil fired combi boiler, which has a 10L reserve tank built into the boiler housing itself. It does look like the stopcock is fully open and the water meter tap is open all the way too. Interestingly, I can’t seem to see a 22mm pipe though - only 15mm. I can only imagine that a new system with a pressurised cylinder will give us much better flow out of the hot taps! We also shower rather than fill a bath, so we shouldn’t ever be in the situation where the cylinder can’t fill quickly enough to keep up…. And 12L per minute cold water flow is clearly not too bad then, compared with some areas. I might take the issue up with Octopus directly, as it is odd that they stipulate a 14L/min flow rate. I’m sure they want the work, as they will receive the grant as well as the payment from us!

matt_drummer

The grant is for the home and any future owners so the installation has to meet standards that have been set to suit any owner or occupier of the property.

Just because you don't want baths somebody in the future might so the system has to be capable of doing so if you want the grant.

You can always just install the heat pump and forgo the grant if you can't meet the standards required.

The tank is small at 150l so it will be easy to empty too fast causing problems with water levels and water pressure.