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Using an air source heat pump with an existing heating system: 5 key things to consider

Posted by John Lightfoot on 15 August 2011 at 9:24 am

I’ve tried below to give an overview of whether you could consider using your existing heating system without going into too much technical hype! (Hope I’ve succeeded – let me know!).

The guidance below will give you some pointers as to whether it is worth considering, but of course your local installer is going to give you much more qualified advice once he has been able to inspect your system.

Normally you can consider using your existing heating system with a Air Source Heat Pump when:-  

1. Your existing heating is a “wet system”
By that I mean it uses water as the heating medium through some form of boiler.

2. Your system is relatively new or has been well serviced and treated with the appropriate chemicals during it’s life to date.

Heat pumps normally have heat exchangers which have very narrow waterways, in order to “scrub” as much heat from the refrigerant as possible. These waterways can therefore become easily blocked by suspended debris in the heating system. You can add a strainer in the system to protect the heat exchanger, but if you have a dirty system this will constantly become blocked and produce “nuisance trip outs” which will prevent your heat pump from operating.  

3. Your heat emitting medium is an underfloor system (if you have a radiator system you will almost certainly need to increase the size of your radiators assuming they currently work on a heating system providing 70C flow water temperatures or above).

Even if you have a heat pump that can produce water at higher temperatures they are normally far more efficient and therefore even cheaper to run at lower flow temperatures.

4. You have a high efficiency domestic hot water cylinder, designed for preheating the domestic hot water with flow temperatures typically obtained from a air source heat pump.

Your existing domestic got water cylinder can always be replaced with a high efficiency version designed to work with heat pumps.

5. Your installer can allow for additional boost heating for those odd days when the ambient (outside) temperature drops below design conditions.

As always, the best way to determine whether you can utilise your existing system, is to speak to your installer who will be able to advise whether using your existing system or part of it, would be a cost effective option.

Photo by Stevendepolo

About the author: John Lightfoot is director at Thermal Energy Ventures Ltd.

If you have a question about anything in the above blog, please ask it in the comments section below.

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1 comments - read them below or add one


scotsguyComment left on: 12 November 2015 at 6:19 pm

I had a Daiken Low temperature Air Source pump fitted, plumbed into exsisting radiators that were originall heated by a coal fire back boiler. The system is at the side of the house away from the bedrooms and is loud enough to be heard in those bedrooms. The radiators never get any warmer than tepid (I can sit with my bare back against them) and the cost seems excessive compared to the coal fire costs. I am not sure if the system was welllooked after or indeed if it was flushed before installation but the house was very damp. The cavity wall insulation was damp and the landlord re-clad and rough cast over the old wet dash (leaving the old insulation in situ. He assured me the new system was so efficient it would soon dry out. I feel the system is no good for the size of the radiators and the High Temp pump shoul have been installed. The house is cica 1920 cavity brick built and is in open countryside.

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