You have to replace all your pipes?

When swapping to a heat pump people may tell you that you have to replace all your heating system pipes. That means ripping up all your floorboards and is disruptive and expensive. It may also be entirely unnecessary; this is another reason why it really makes sense to get the survey and calculations right at the start before any work starts. It could save you a lot of money and hassle.

This handy table I made shows how much heat you can get down various sizes of pipe, based on a target flow rate of 1m/s.

Why 1m/s? 

Above a flow rate of 1.5m/s in a heating pipe and it gets annoyingly noisy, and the water can corrode fittings. Below 0.5m/s and sludge is deposited in the pipes, not the filter, which you don't want either. So generally 1m/s is the sweet spot we, and other heating professionals, aim for.

dT stands for deltaT - it means temperature difference in ancient Greek. I'm not sure why we're using ancient Greek, but we kind of stuck with it now. (Incidentally did you know that "heat pump" is apparently "θερμαντικὴ ἀντλία" in ancient Greek? Not that I have any idea how to even say that!)

A key difference between heat pumps and standard boilers is the deltaT. 

Compared to a gas boiler a heat pump system needs get the water down the pipe faster to deliver the same amount of heat - 3-4 times faster. 

Imagine the heating ring main - that's the hot and cool pipes running near every radiator in the house - had been done in 15mm copper.

Looking at my chart it looks like we could get around 12kW down that pipe at dT20, and 3kW at dT5. 

So, do we need to rip up all the floorboards and replace the pipes?

Well a different option woudl be to split that single ring into two - upstairs and downstairs probably makes sense. We can now get 3kW to each floor, or 6kW in total. That's plenty for a great number of UK houses where the peak heat load is 6kW or less.

If we had to we could increase the dT to 7 - now we can get 4.3kW to each floor, or 8.6kW in total. 

More often you find that the existing pipe for the ring main for a gas boiler was done in 22mm (because that was the "done" thing), this was arguably too big, but it helps us out when swapping to a heat pump!

Now we can get 6.7kW down those 22mm pipes, or over 13kW if we split the ring into two, or 9.4kW if we increase to dT7, or nearly 20kW in total if we split the ring into two.

So.... a little initial maths may mean that the crowbar can get a break!  

Are you thinking of switching to renewable heating? Some initial effort spent on a surveys and calculations can save a lot of money and disruption! We like to design heating systems that are "as simple as possible, but not simpler". This often means you save money because less kit is needed, there's less time spent on labour, and the running costs are lower.    

Get in touch with us to find out how we can help.