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Split system and pipe lengths for air source heat pump installation

Air Source Heat Pumps (ASHPs)

Last Post by nickmorgan 6 months ago

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nickmorgan

(@nickmorgan)

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Joined: 7 months ago

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Topic starter 11/03/2025 9:05 am

Hi all,

I’m in the process of getting a few quotes for an ASHP installation. We have a passageway to the side of of our house but it is narrow and we’ve been advised it’s an unsuitable location for the ASHP. We have two options:

1. Locate at the front of the house (north side). Not ideal aesthetically but we think we can position in a way that’s not obtrusive.

2. In the garden, about 10m away from what will be our plant room. Also not ideal aesthetically but I’ve seen some pictures of nice panelling to cover the ASHP. We’re also considering a split system with a smaller outdoor unit in the garden with the main processing done in the plant room.

I have two main questions:

1. Does front or back (north or south) of the house make any difference to performance?

2. Is there an optimal distance beyond which an ASHP in the garden doesn’t perform well? And what about rodents chewing away at the pipe work - has anyone had problems with this and/or good solutions?

Thanks,

Nick

This topic was modified 6 months ago 2 times by Mars

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JamesPa

(@jamespa)

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11/03/2025 9:20 am

Posted by: @nickmorgan

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1. Does front or back (north or south) of the house make any difference to performance?

Not materially, the amount of air shifted when its cold means that its essentially sampling the general air temperature. If it can be in full sun then it probably helps with defrosts on cold sunny days, but we dont get many of those sadly so not worth busting a gut over.

Posted by: @nickmorgan

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2. Is there an optimal distance beyond which an ASHP in the garden doesn’t perform well? And what about rodents chewing away at the pipe work - has anyone had problems with this and/or good solutions?

Pipework, if of any length, should be buried in something like this Its incredibly expensive, needs to be about 750mm deep so the trenching costs a lot, and it has a bend radius of about 1m, so basically a bit of a ***. You can make it up yourself but it needs to be done well and properly sealed. @johnmo has I believe. Avoid if at all possible and if not make sure its done properly in a way which will stand the test of time.

As to distance, in principle anything is possible with the right water pump (but make sure they dont use it as an excuse to fit a buffer tank!) but as a very rough guide 20m = very roughly 300W in loss and you may need an auxiliary pump.

Split is easier, the refrigerant lines are much more flexible, dont need as much insulation, and distance is not a problem. However the installer needs an f-gas certificate and few domestic installers have it. All commercial ones do but they generally only do air to air.

Given your choices I would probably go for the front!

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Anonymous 5011

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11/03/2025 12:41 pm

Posted by: @nickmorgan

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1. Does front or back (north or south) of the house make any difference to performance

In general no, the amount of air drawn through unit means it gets the air temperature not any localised warming. Front of house is within permitted development rules so really needs planning permission.

Posted by: @nickmorgan

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2. In the garden, about 10m away

Not that far, I am about about 15m. Slight drop in CoP but nothing to worry about. Still routinely get a cop of about 5 when running. My unit is behind shed, shed is insulated. Pipe runs outside shed above ground for 2m, then into shed and around it inside), then out and underground, up and through house wall. Made my own underground pipes (28mm Hep2O, 25mm closed cell insulation, aluminium tape wrapped, then inserted in to double wall 110mm underground pipe. Sealed ends with stainless mess and expanding foam.) buried about 600mm.

Split - leave everything outside if you can.

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nickmorgan

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Topic starter 11/03/2025 4:08 pm

@johnmo Do you have any photos to show the pipe journey in your installation?

And when you say leave everything outside in the split system, do you mean all elements excluding the hot water cylinder?

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nickmorgan

(@nickmorgan)

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Topic starter 11/03/2025 4:08 pm

@jamespa 👍

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Anonymous 5011

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11/03/2025 5:18 pm

Posted by: @nickmorgan

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And when you say leave everything outside in the split system, do you mean all elements excluding the hot water cylinder?

Poor wording by me. Meant to say go mono-bloc heat pump so everything stays outside. A split system can move all the noisy stuff inside the house.

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