Extension to 1920s house - what heating?

[osprey]

I am at the earlys stages (architect involved) of planning a double height extension to a 1920s build detached house. It will convert an 'L' shaped house into a square, the extension having a 5 x 5m footprint. So one quarter of the house will have a new ground floor, the rest being suspended wooden floor.

 

What heating should I go for in the extension? 

1) UFH in the screed. The rest of the house has radiators currently. Plan to insulate underfloor rest of house, so retrofit UFH could be possible later

2) Radiators. Matching the rest of the house.

3) Radiators now, possibly  surface mount UFH added to both old and new floor later if it made sense.

 

In 1, the ufh would have a very different thermal response to the rest of the house, (slow to heat/cool) and require additional plumbing etc.

 With 3, I  am not sure if UFH heating alone would ever make sense for an old house, but radiators + retrofit, surface mount UFH might remove the need for oversize radiators if ASHP beome the norm?

 

Any thoughts welcomed, thanks.

[Russell griffiths]

Two. 

[osprey]

5 hours ago, Russell griffiths said:

Two. 

Thanks.

The reply certainly had more brevity than the question. Any particular reasons?

(Are would be part of extended kit hen/sitting area/.

[Russell griffiths]

Original house will be poorly insulated and airtight, your new extension will be better but still not amazing. 

Your old house will require fairly high heat being pumped into the rads. 

New floor will need lower temps adding to it. 

Trying to get a general plumber to sort out that will be hard work, the builder you use will probably have his own plumber who understands rads, it’s just an easier option to mitigate against it all going a bit tits up. 

 

If if you were doing a full £200,000 Reno, all floors out, loads of insulation everywhere then it might be a bit more beneficial to go ufh everywhere, but for a little infil I don’t see the point in mixing up something that works. 

[saveasteading]

It would depend on more specific details. 

If you build the new to very high spec, and can close doors from old to new, then it might be worth heating as if it was a new house. so ashp and ufh an option.

Or leave the  existing system alone and install all new including boiler. That way it will be a small unit, lower cost, and minimal disruption.

Also no quirks in the joined up system you would otherwise have

And if the old system has problems, the house is still up and running.

I understand it can be more efficient to use 2 small boilers than one, except in the coldest of conditions.....but may be wrong.

[osprey]

OK, understood, but many houses have UFH to the ground floor, but rads to the bedrooms, so running a 'mixed system' do they not? 

[saveasteading]

10 minutes ago, osprey said:

rads to the bedrooms,

Big, special rads for the lower temperature water.  ProDave and others have discussed whether you just allow downstairs air to rise and heat the upper rooms.

[ProDave]

24 minutes ago, saveasteading said:

Big, special rads for the lower temperature water.  ProDave and others have discussed whether you just allow downstairs air to rise and heat the upper rooms.

In a house close to passive house levels of insulation and air tightnes, yes, in a 1920's house, almost certainly not.

[osprey]

40 minutes ago, saveasteading said:

Big, special rads for the lower temperature water.  ProDave and others have discussed whether you just allow downstairs air to rise and heat the upper rooms.

I had a chat with a chap from a company which does ufh, both regular and retrofit surface mount. He said the retrofit/surface mount stuff was designed run with hotter water, both for faster response times and to be easier to mix with normal rads. Of course this would not then be suitable (I assume) for ASHP applications. 

A builder I spoke with about the project suggested SM UFH, as he does it 'all the time'.

 

But I am not convinced, hence the question here: thanks for the useful comments.

[PeterW]

4 minutes ago, osprey said:

I had a chat with a chap from a company which does ufh, both regular and retrofit surface mount. He said the retrofit/surface mount stuff was designed run with hotter water, both for faster response times and to be easier to mix with normal rads. Of course this would not then be suitable (I assume) for ASHP applications. 

A builder I spoke with about the project suggested SM UFH, as he does it 'all the time'.

 

But I am not convinced, hence the question here: thanks for the useful comments.

First rep is talking crap - unless he knows every floor type you’re planning then “just running hotter” isn’t an option ! You cannot dump 65°C water into UFH and hope it works ..! 

 

SM - or retrofit UFH - only works when you have lots of insulation and can lose the 25mm of build up in door frames etc, and it’s really a bit of a fudge of a solution. 
 

I would stick with rads and oversize them for the requirement based on the heat loss of the rooms, size them at D30°C rather than D50°C so if you decided to go with a heat pump in the future they wouldn’t need swapping. 
 

If you’re hacking the system about then consider repiping the whole house but as a minimum get the old system properly power flushed and consider adding new radiators throughout.

 

 

[osprey]

Thanks for reply.

Ceilings are 2.7m high, and I could accomodate 25mm build-up if needed, and plan to include under-floor insulation, but  there is a limit as to what can be done with an old house.

Rads throughout look like the plan at the moment. Current CH system is about 10 years old. I will look at increasing radiator size in the future if/when needed, and also when I get a better idea of the house's thermal performance following the improvements.