keeping old boiler with new heat pump

darida

I currently use an oil combi boiler central heating but I am considering to switching to an air heatpump. However, being aware of the potential downsides I am wondering, if there is the option to keep my old boiler so that I can either be able to switch between the two, or at least have the option to go back to using my old boiler if the heat pump system proves inefficient or too expensive to run. I had a survey done and it appears that the pipes to radiators will not be changed and only some of the radiator will be replaced with new ones for the new heatpump system. I am not really looking for a hybrid system. Simply the option to be able to go back to combi boiler if the heat pump is not what I have hoped for. Any advice or suggestions on this would be much appreciated.

DougMLancs

You can run them as a bivalent system where the air source heat pump does most of the work and then your existing oil boiler would kick in if needed. Nothing to stop you taking the ASHP back out again but that would be a huge amount of money wasted. I would suggest you’re much better off making sure the ASHP system is well-designed so that it runs at maximum efficiency. What were the results of your heat loss calculation and what size heat pump was suggested? Do you know what flow temperature they’re designing for with the radiators?

lohr500

Not sure if you are planning to claim the £5000 Govt grant towards an ASHP, but keeping the old boiler might class the system as "hybrid" which would exclude you from the grant. You may need to investigate this further.

Also, the fact that you have a combi boiler will probably result in more complex pipework and valve switching to integrate the boiler with an ASHP. Presumably the ASHP will need a hot water storage tank/heat exchanger of some type, whereas the combi boiler is designed to provide direct on-demand hot water to the hot taps/shower/etc.

matelodave

A properly designed system should work and heat the house and hot water, even when it ever so cold outside - ours does.

Most of the "downsides" that you may be aware of are usually the result of a poor design and not knowing how to use the system properly and hearsay.

As said above, it's possible to integrate one into a bivalent system, but there's not much point in spending out a lot of money on a system that you don't trust.

darida

Thank you for the hints. I do indeed intend to get funding towards the heating system (and insulation) through ECO4. I do not intend to run the old boiler with the ASHP; not even having them connected/installed together. My concern is that if the new ASHP proves to be the wrong choice (either too expensive to run, or not able to cope with my heating needs) I would like to know that I can go back to my old combi boiler (or a new boiler) at a relatively affordable cost of re-installation.

I am having a final survey by the potential installers next week and hopefully they will give me the heat loss calculations and technical elements of the proposed system then. My previous survey was conducted by the company that handles the funding so they only provided me with general indications of potential changes that will take place in the property and central heating as well as the specifics on the insulation measures to be applied.

Reed_Richards

There is nothing fundamentally different about a heat pump that would prevent you swapping it out for an oil boiler. 

There is no combi heat pump, you will need a hot water cylinder when your heat pump is installed.  If you then reverted to a combi you should plumb the hot water cylinder as if it were another heating zone (a small alteration to your plumbing and wiring).  You might plumb the hot water from the combi to the nearest hot tap just so the hot water side gets used sometimes.

An oil boiler running a heating system designed for a heat pump would operate at a higher output water temperature so would heat the rooms very rapidly.  So it might tend to run in short on/off cycles, particularly in warmer weather.  Short cycling can lead to reduced efficiency.

        

Dotdi

darida said:

I currently use an oil combi boiler central heating but I am considering to switching to an air heatpump. However, being aware of the potential downsides I am wondering, if there is the option to keep my old boiler so that I can either be able to switch between the two, or at least have the option to go back to using my old boiler if the heat pump system proves inefficient or too expensive to run. I had a survey done and it appears that the pipes to radiators will not be changed and only some of the radiator will be replaced with new ones for the new heatpump system. I am not really looking for a hybrid system. Simply the option to be able to go back to combi boiler if the heat pump is not what I have hoped for. Any advice or suggestions on this would be much appreciated.

We had a heat pump put in on a scheme but now wish we had kept the oil boiler so that we could use that too. I would stick to your boiler for now as radiators don’t get very hot on heat pump. Also when the weather gets cold the heat pump does not heat up well. Ours is only 12 month old, for us not a good swap and very expensive. If you are going to have one keep your boiler too just in case. 

QrizB

Dotdi said:

darida said:

I currently use an oil combi boiler central heating but I am considering to switching to an air heatpump. However, being aware of the potential downsides I am wondering, if there is the option to keep my old boiler so that I can either be able to switch between the two, or at least have the option to go back to using my old boiler if the heat pump system proves inefficient or too expensive to run. I had a survey done and it appears that the pipes to radiators will not be changed and only some of the radiator will be replaced with new ones for the new heatpump system. I am not really looking for a hybrid system. Simply the option to be able to go back to combi boiler if the heat pump is not what I have hoped for. Any advice or suggestions on this would be much appreciated.

We had a heat pump put in on a scheme but now wish we had kept the oil boiler so that we could use that too.

"The scheme" would have ghad to charge you an extra £7500 if you'd kept your boiler.

Dotdi said:

 radiators don’t get very hot on heat pump.

The radiators don't need to get very hot, though. They need to be just hot enough.

Dotdi said:

Also when the weather gets cold the heat pump does not heat up well.

If your heat pump isn't keeping you warm, it'll be one or more of the following:

• Poorly designed system;
• Poorly installed system;
• Poorly operated system;
• Poorly maintained system
  

Have you sopoken to your installer about this?

Dotdi said:

If you are going to have one keep your boiler too just in case. 

For the £7500 cost it might not be a good choice.

FreeBear

QrizB said:

Dotdi said:

 radiators don’t get very hot on heat pump.

The radiators don't need to get very hot, though. They need to be just hot enough.

Over Christmas, my heating system had been running at a little under 35°C at times. Hardly noticed the radiators getting "hot", yet the temperature gauge still went up. Not particularly fast mind you, but then low temperature heating systems are never about speed. As long as the radiators are appropriately sized for the property, barely warm is usually plenty hot enough.

NedS

FreeBear said:

QrizB said:

Dotdi said:

 radiators don’t get very hot on heat pump.

The radiators don't need to get very hot, though. They need to be just hot enough.

Over Christmas, my heating system had been running at a little under 35°C at times. Hardly noticed the radiators getting "hot", yet the temperature gauge still went up. Not particularly fast mind you, but then low temperature heating systems are never about speed. As long as the radiators are appropriately sized for the property, barely warm is usually plenty hot enough.

Same here - during the recent cold snap we have been running 30C flow temps overnight and 32-35C flow temps during the day to heat our old poorly insulated house. The radiators barely feel warm but the house is at the desired temperature - that's how heat pumps work best.

Nick_Dr1

Dotdi said:

darida said:

I currently use an oil combi boiler central heating but I am considering to switching to an air heatpump. However, being aware of the potential downsides I am wondering, if there is the option to keep my old boiler so that I can either be able to switch between the two, or at least have the option to go back to using my old boiler if the heat pump system proves inefficient or too expensive to run. I had a survey done and it appears that the pipes to radiators will not be changed and only some of the radiator will be replaced with new ones for the new heatpump system. I am not really looking for a hybrid system. Simply the option to be able to go back to combi boiler if the heat pump is not what I have hoped for. Any advice or suggestions on this would be much appreciated.

We had a heat pump put in on a scheme but now wish we had kept the oil boiler so that we could use that too. I would stick to your boiler for now as radiators don’t get very hot on heat pump. Also when the weather gets cold the heat pump does not heat up well. Ours is only 12 month old, for us not a good swap and very expensive. If you are going to have one keep your boiler too just in case. 

We are the opposite. We had a heat pump to replace our oil boiler last year and its a revelation. Even during the recent cold snap, its all been fine and I suspect the costs are comparable with oil. Difficult to establish accurately because you don't know how much oil you are using each day - only how long between fills. What I do know is that we are using about 20% less heat than the survey predicted for the design temperature which gives confidence that the heat loss survey was pretty good and the estimate of radiator sizes can be trusted.

Actual cost then is entirely linked to what price you can get electricity for. Get a good tariff and you will be fine. Stay on a standard tariff and it will get expensive. You do not have this option with oil - you pay the monopoly price on the day you need it.