Trying to find a solution...

[PeterW]

20 minutes ago, Mr Punter said:

Is there any point in having a very low output heat only boiler for the UFH plus a BFO combi for hot water?

Not really as the low heat limit is about 4.2kW, but that is at flow temps of 63°C which is far too high for UFH. I’ve looked at a few options recently but any heat requirement less than 6kW constant and I am struggling with gas boilers without 150 litre buffers. 

[ZacP]

1 hour ago, Mr Punter said:

Is there any point in having a very low output heat only boiler for the UFH plus a BFO combi for hot water?

I had this as an idea too. Like a 10kw for UFH and a 38kw for hot water.

I just need convincing that although ASHP seems lovely on the surface it genuinely is the best option for us.

[SteamyTea]

10 minutes ago, ZacP said:

I just need convincing that although ASHP seems lovely on the surface it genuinely is the best option for us.

Do you accept that ASHP (actually all heat pumps) need to be 'plumbed' differently that a gas combi?

If you do, then it is just a case of designing both systems, costing them out, and seeing which comes out on top.

[ZacP]

8 minutes ago, SteamyTea said:

Do you accept that ASHP (actually all heat pumps) need to be 'plumbed' differently that a gas combi?

If you do, then it is just a case of designing both systems, costing them out, and seeing which comes out on top.

Yes I understand that they are both different systems that need installing differently.

I guess costing is the next step. If however we can’t use gas boilers for UFH without a tank then we may as well use a HWC in the loft anyway and just do it that way even tho it’ll be a bit more inconvenient for installation and maintenance but better on a day to day living. 

[ZacP]

So... 

 

Option 1 - 1x combi for both hot water and heating (Vaillant EcoTEC Plus 938) £2000

 

Option 2 - 2x combi

BAXI 228 GAS COMPACT COMBI BOILER (heating temp range 20’ - 80’) £600

And

Vaillant EcoTEC Plus 938 (hot water) £2000

 

Option 3 - ASHP £5000 (12kw Samsung)

300l horizontal hwt £900

 

All obv plus installation and associated plumbing... 

 

[Mr Punter]

2 hours ago, PeterW said:

Not really as the low heat limit is about 4.2kW, but that is at flow temps of 63°C which is far too high for UFH. I’ve looked at a few options recently but any heat requirement less than 6kW constant and I am struggling with gas boilers without 150 litre buffers. 

 

I thought the water was blended with cold in UFH.  Surely there is something you can have to stop the boiler firing due to a call from the UFH cicuit for at least an hour, to stop it cycling?

 

We are in a fairly average spec new house and the heating is mostly only on from December to March.

 

In a previous new house we had UFH and the boiler shut down mid winter and it was a day before we noticed.

[joth]

43 minutes ago, Mr Punter said:

Surely there is something you can have to stop the boiler firing due to a call from the UFH cicuit for at least an hour, to stop it cycling?

Yes, isn't that thing called a buffer tank?

I'm confused why anyone would consider the expense of installing and servicing and maintaining 2 gas boilers when you could just have one plus a buffer tank?

 

 

[PeterW]

55 minutes ago, Mr Punter said:

 

I thought the water was blended with cold in UFH.  Surely there is something you can have to stop the boiler firing due to a call from the UFH cicuit for at least an hour, to stop it cycling?

 

We are in a fairly average spec new house and the heating is mostly only on from December to March.

 

In a previous new house we had UFH and the boiler shut down mid winter and it was a day before we noticed.

Problem isn’t when they are initially firing, it is when they start to close down and blend off the hot as the cold return increases in temperature. What happens is the flow rate through the mixer valve reduces so the boiler stops firing. As the hot is now cooling and the flow into the mixer continues then the boiler senses the cold flow and fires - short cycling the boiler. This can be for 3-4 minutes in every 15 and destroys boilers and gas valves, and as they never get to condensing temperatures the efficiency is significantly lower. Even a 50 litre buffer can help if there isn’t the space for bigger buffer tanks. These can be had for £200 and with an immersion in them too, they allow for standby heating in the event the boiler fails.