Heat Pumps: anyone have one/thought about it?

[RockLobster]

I have 8mm plastic pipework to my rads so I’m thinking it’s going to a big job.

 

[b0rn2sk8]

I have 8mm plastic pipework to my rads so I’m thinking it’s going to a big job.

Are you sure it’s 8mm plastic?

IIRC, 10mm is the smallest size plastic they do.

 

[RockLobster]

Are you sure it’s 8mm plastic?

IIRC, 10mm is the smallest size plastic they do.

I assumed it was 8mm. If yours was 10mm plastic did you have any pipework replaced? Did you have any new radiators? I’ve read Octopus won’t touch microbore 10mm that is. And I assume it’s working great for you?

 

[RockLobster]

This is my pipework. Has to replace a section as it was sludged up.

 

[b0rn2sk8]

I assumed it was 8mm. If yours was 10mm plastic did you have any pipework replaced?

I’ve got 10mm plastic microbore and no replacement needed in my install. My total heat loss is just under 6kw.

10mm plastic is usually 10mm OD, ID is just over 8mm as they have plastic inserts which fit into the end of the pipes at the joints. 8mm is usually copper.

Did you have any new radiators?

Yes, loads. 5 upstairs, 3 downstairs.

I’ve read Octopus won’t touch microbore 10mm that is. And I assume it’s working great for you?

They will do an anything down to 10mm micro bore. It works fine for me and my house/heat loss.

10mm puts a lower cap on how much water (and therefore heat) the system can supply to a radiator as it can’t flow as much water as say a 15mm copper pipe.

It effectively caps the maximum output of a radiator at a lower level than 15mm copper. As long as you are below that cap for that room, you are fine.

You can of course have multiple radiators to a single room to get around any limits, larger rooms probably already have more than one radiator already anyway to help spread the beer around the room.

Edit: your house looks fairly modern so probably doesn’t have a huge heat loss and will probably be fine on 10mm

 

[shroomz]

I have 8mm plastic pipework to my rads so I’m thinking it’s going to a big job.

My install is 8mm copper to each radiator from 22mm main distribution headers. There are two separate problems to calculate and resolve:
1. Your heat loss per room at your design condition
2. Head (predominantly friction) loss in each circuit.

Your case sounds worth doing detailed calculations to identify your worst case circuit. In my case it was my living room that is furthest away from the heat pump with greatest length of 8mm, and also the highest heat loss at around 1.3kW when it's -5 outside. The most water you can get down 8mm copper is worth around 1.1kW at dT of 5. I got a Nibe heat pump that runs with a dT of 7, and also the other rooms have capacity to balance the living room.

So far it's worked well. We've not had -5 but the house has kept a steady 18C throughout since July. If you want to investigate in detail or better yet find out if the installers you are talking to are willing to put some thought into it, check out this heat geek article and video:

HeatGeek: What to do with microbore pipework on heat pumps

For heat pumps to work efficiently we need flow, and this does 2 things. It will mean the heat pump’s plate heat exchanger will work at maximum efficiency AND

www.heatgeek.com

Heat Pump Piping: Do You Really Need to Upgrade Your Pipes?

Get expert guidance on heat pump piping sizing! Our comprehensive guide covers everything you need to know about heat pump piping sizes.

www.heatgeek.com

Once you've gone through these if you're keen and have any questions there are some knowledgeable folk here and on other forums.

It's not perfect with 8mm (or effectively 8mm if you have 10mm plastic which has greater friction inside as well as the inserts) but there are ways to resolve it, or you could repipe.

 

[RockLobster]

Thanks both. House built in 2003 so no wall or floor insulation. In the last 12 months I’ve replaced all windows and last week new Endurance door. This has helped. I had the loft partially boarded properly. There are some things I want to sort out in the loft. Install thermahoods for spots and top up insulation on the sides. For instance tonight I haven’t put the heating on since last night and it’s holding just above 18 degrees. Last night it was on for 30 minutes set to 18. Mind you it’s 8 outside so not freezing.

House is 4 bed detached. 1800 square foot.

@b0rn2sk8 do you have wall insulation?

 

[b0rn2sk8]

Yes, your house was built the same year as mine. You should have cavity wall insulation and floor insulation. I’m pretty sure cavity wall and ground floor insulation was compulsory form the early 90’s.

Sure it’s not as thick as what you’d get in a 2020 new build but it should have some and way better than say an 80s build which will have nothing. They will build that into their assumptions.

Your heat loss will probably be in the region of 6kw if you have topped up the loft to ~300mm. That is absolutely no problem on 10mm plastic microbore and 22mm flow/return on the central heating.

Ours is slightly smaller 4 bed detached at 130 square meters. Our heat loss is about 5.5kw with terrible double glazing and a minimum of 250mm in the loft. It’s higher where it isn’t boarded (~50%) but they used 250mm for the purpose of the survey.

We have a 6kw Daikin unit (which is just a software de-rated 8kw heat pump), when it’s on tickover it draws about 400w. The most I’ve seen it draw is 2.2kw when on full charge doing hot water at 55C flow temperature.

We have a gas fire in the lounge, this added a huge number to the heat loss, 1000w if I recall correctly. We’ve never used it and the gas was being disconnected as part of the install. They ignored it for the purpose of the survey and I filled the flue with expanding foam before they installed. I’ve not got round to removing it yet and bricking up the hole, it’s a job for the spring.