Renovation - conversion to low temperature heating

Renovation - conversion to low temperature heating

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Church of Noise

Original Poster:

1,453 posts

236 months

Monday 30th November 2015
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Dear all,

The GF & I bought a 1958 house and are having it renovated.

We decided early on to have underfloor heating downstairs, yet on the first floor, this is not possible.
An additional bit of info is that we decided to use the Honeywell Evohome system.

First idea was to have two separate circuits, one for the UFH (low temp) and one for the radiators on the first floor ('high' temp, as it was). This brings some practical things to consider, and we decided to either go for
  • a solution with a gas boiler that can run two separate circuits (http://www.ithodaalderop.be/producten/cv-ketels/cube-duo/ in Dutch, sorry). Downside here is that the Evohome can't communicate using Opentherm with this system, which would mean it would only work on/off, not modulatingly.
  • the replacement of all radiators, so the entire installation is converted to low temperature heating. Downside of this obviously is the additional cost for 4 radiators (bath room + 3 bed rooms). Upside is that we have quite a range of boilers to choose from.
What solution would you suggest?

Thanks!

Gingerbread Man

9,171 posts

212 months

Monday 30th November 2015
quotequote all
Why can't you run under floor heating upstairs? It's possible.

Any boiler can run the two zones via zone valves.

TA14

12,722 posts

257 months

Monday 30th November 2015
quotequote all
Church of Noise said:
* the replacement of all radiators, so the entire installation is converted to low temperature heating. Downside of this obviously is the additional cost for 4 radiators (bath room + 3 bed rooms). Upside is that we have quite a range of boilers to choose from.

What solution would you suggest?
Considering how much you'll be spending for UHF, a boiler, a fancy control system and whatever else the cost of four rads won't be that much, even so I would suggest that you follow gingerbreadman's advice.

Church of Noise

Original Poster:

1,453 posts

236 months

Monday 30th November 2015
quotequote all
Gingerbread Man said:
Why can't you run under floor heating upstairs? It's possible.

Any boiler can run the two zones via zone valves.
Fair point, however we are not tackling the first floor yet (largely because of the available budget).

Agreed that the investment for the new radiators is not very large relatively speaking... Yet at a certain point in time, one needs to keep an eye on total spend,hence the question.

Gingerbread Man

9,171 posts

212 months

Monday 30th November 2015
quotequote all
anonymous said:
[redacted]
Less water carried within, less water to heat up, quicker reaction times. Typically run from a manifold and therefore self balancing give or take.

I still hate the stuff.

Too Late

5,092 posts

234 months

Monday 30th November 2015
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I would spend the money and get underfloor heating everywhere......

Church of Noise

Original Poster:

1,453 posts

236 months

Monday 30th November 2015
quotequote all
Thanks for the valuable input!

One more question: the guy who's going to install the heating system said that by defining a zone for each room could cause problems: when only one room with a radiator needs to cover a (limited) temperature drop, the boiler would generate too much power (because it can't be modulated between 0% and 100%) and as such cause for quite the loss in efficiency. This however contradicts some users' very positive experience with the system.

Does anyone have a view on this please?

Gingerbread Man

9,171 posts

212 months

Tuesday 1st December 2015
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UK Boilers just output one temperature which the hot water cylinder coil and the radiators have been designed to work with. Underfloor heating in the UK works off a manifold which incorporates a blending valve for the temperature management and and a shunt pump. Each loop (there could be multiple loops per room if large spaces) can be individually controlled via a thermostat if required. Or you can have a stat do them all.

A quick look at the Evohome website states that it supports up to 12 zones. I've no personally hands on experience. I guess it would work just fine with zone valves and a typical system, but not the multi zoned boiler.

So you'd typically have a zone valve for the hot water cylinder, one for the UFH manifold, or more if there are multiple manifolds and then you could have one for the upstairs radiator circuit.

Is that how it's done in Belgium?

Pheo

3,324 posts

201 months

Tuesday 1st December 2015
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I think the plumber is getting at that you need a sufficient temperature drop against the outflow vs the return in order for the boiler to be running in high efficiency / condensing mode. If you have it powered up running only one radiator, then in theory it will be turning on and off a lot as although it can modulate to a degree it can't do 1% or whatever. My understanding from reading on here is that the boiler is most efficient when there is a large drop (10c +) across the two pipes.

Hope that helps a bit

Church of Noise

Original Poster:

1,453 posts

236 months

Tuesday 1st December 2015
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Gingerbread Man, Pheo,

Thanks for your views.
You more or less confirm what I was thinking, and I shall probably have a limited number of zones (ground floor and first floor) to avoid the issue Pheo described, the other radiators at the first floor can then remain 'normal' ones. They're only for the bedrooms anyway.