Talk:Central heating design

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--John Stumbles 18:54, 4 January 2007 (GMT)

Under pipe layout you missed one: radiator on the hot water circuit :). Not as rare as it should be. NT 22:30, 13 January 2007 (GMT)

UFH Efficiency

How is ufh more efficient? Elevated slab temp would surely mean more heat loss than rads? NT 07:36, 15 January 2007 (GMT)

If the floor is not well insulated from the walls you get heat loss through the walls and, for ground floors, into the soil outside. I don't have a link for it but recall reading of a post-WWII housing development in the USA which had UFH in the floor slabs which weren't insulated from the walls. Gardeners living in these houses thought they had green fingers (or green thumbs as they say over there) because the warming of the surrounding soil allowed everything to grow early! Of course fuel was cheap then and there so I guess they weren't too bothered about their fuel bills. (The UFH was also in copper pipe so these installations all corroded through after a few decades and most of the remaining housing stock now has conventional heating systems.)

However assuming one has floor slabs properly insulated from the walls and otherwise correctly installed UFH I understand the amount of heat needed to make a room comfortably warm is substantially less than with radiator-based systems where much of the heat goes into warming the air which accumulates at the ceiling and gets lost through ventilation. It would be good to give some references when I (or anyone else) fills out that part of the article but I was still just roughing it out.

--John Stumbles 11:52, 15 January 2007 (GMT)

It'll be interesting to read about that once its done. NT 19:20, 15 January 2007 (GMT)

Warm walls

I was going to add a brief comment about warmed interior stud walls as a radiator alternative, but was unsure where to put it. Walls are listed under 'other radiant' but I was thinking convection not radiating walls, just like large low temp radiators, which are of course convectors rather than radiators. NT 01:37, 5 February 2007 (GMT)

I've not heard of these. Sounds as if they would work by radiation (like UFH) rather than convection but that it would be difficult to get the sort of heat output you'd get from warmed solid walls or floors. Do you have any more info e.g. where they've been used, sort of construction techniques, heat ouptuts etc? --John Stumbles 09:37, 5 February 2007 (GMT)

OK I've started a thread on uk.d-i-y called Look. no rads. NT 11:07, 5 February 2007 (GMT)

Convection or radiation?

Low temperature surfaces like radiators, UFH, warmed walls etc do not gt hot enough to produce significant radiant heat, so these are all convection/conduction heaters. NT 20:05, 6 February 2007 (GMT)

I thought any warm body radiated heat? How much it emits by radiation depends on the temperature difference between it and its surroundings (since they are also radiating) but it should be a linear relationship.

As someone pointed out in your thread on warm walls "radiators" have vastly greater output when they have multiple panels and fins behind/between the panels, which can only affect convection. You can see shimmer in the air rising above a "radiator" and see dust stains on the walls above them and other evidence of convection. You don't get any of this with UFH yet you can feel the warmth coming off it even if the air is cold, so I guess that is radiation. I would expect warm walls to have a greater convection effect than warm floors because they'd encourage warmed air to 'slide' upwards and get a convection circulation going (thus nicely warming the ceiling!). However I suspect you have to place a warm body in free air to really encourage convection - which is what rads with fins attempt to do.

--John Stumbles 00:47, 7 February 2007 (GMT)

I dont believe there is a linear relationship between temperature and radiation.

For a filament bulb, efficacy/EFFICACY = (temperature/TEMPERATURE)^4.52

Which means that as temp halves, light output drops by around 2^4.52 = a factor of 23.

This is why low temp water based heating produces almost no radiant heat. NT 02:22, 7 February 2007 (GMT)

Maybe we should take this discussion back to the group? I've started a new thread: Convection or Radiation? John Stumbles 10:37, 8 February 2007 (GMT)

radiator on HW circuit

I've removed this section

radiator on HW circuit This is never an advisable option. It is found with some existing heating systems, and is almost always due to mistaken connection. Unless the radiator is a combined towel warmer and radiator in use in a bath or shower room.

Signs of a radiator on the HW circuit are:

  • Radiator comes on sometimes in summer
  • Radiator sometimes fails to come on when other rads do
  • Insufficient heating in the affected room

The solution is to replumb. Unfortuntely this means cost and time inputs, and sometimes these are not available. There are workarounds which may prove adequate, but are never ideal.


  1. it was in the section on pipework layout whereas this is about configuration
  2. I've added discussion of rads on DHW circuits to the configuration ("Controls and Zoning") section
  3. discussion of faults in CH systems (whether from original design or arising from faults in components) belong in the Central Heating Operation article (which doesn't yet exist but please feel free to write it!)

As I wrote in the Controls and Zoning section some rads, especially in bathrooms, are/were sometimes deliberately connected across the DHW or otherwise differently from other rads. The pros and cons of such arrangements are open to discussion but I think it's important to understand where such arrangements are intentional and what the intent is rather than writing them all off as cock-ups (though undoubtedly those exist too!).

I take the point that its not really design. Its useful material, but not sure what article heading t put it under. NT 19:18, 12 February 2007 (GMT)

I've started a Central Heating Repair article - currently just an outline/skeleton - and put the point about rads on the DHW in there.

--John Stumbles 19:12, 15 February 2007 (GMT)

Additional Thermostats

The section Additional Thermostats is actually about additional zones and should go in the section on zoning.

--John Stumbles 23:19, 15 February 2007 (GMT)


Filled in the section on radiator locations. --Makewrite 00:41, 28 February 2007 (GMT)


Is there a particular reason you used "nowiki" tags around words you put in quotes? They don't seem to have had any visual effect and I'd have thought they could be left out. -- 00:44, 2 March 2007 (GMT)

I was simply trying to get a word in quotes. Adding quotes make wiki do wonderful but unwanted things. Anway feel free to edit as you wish - as if I needed to say that. Also added saection of routing of pipes --Makewrite 23:11, 5 March 2007 (GMT)

Ah yes! 'One quote' two quotes three quotes "double quote chars" --John Stumbles 23:18, 5 March 2007 (GMT)

joist notching

Added stuff about joist notching. ... which was wrong.

Ah! I naturally assumed Two-Jabs had slipped another one through :-) --John Stumbles 00:14, 10 March 2007 (GMT)

Structure of article

do we need to break this page into design and installation pages? --Makewrite 22:45, 9 March 2007 (GMT)

The installation bit isn't too big at the moment, but there are a few sections which have got quite big and are making the article a bit heavy to take in in one go. It might be time to split most of the contents of the sections into their own articles with this page being an intro and index to them.

Needs a Round Tuit I think!

--John Stumbles 00:14, 10 March 2007 (GMT)

OK Controls and Zoning split off, next up Rads methinks --John Stumbles 16:39, 14 March 2007 (GMT)

Some links which may be useful