The original 1970s in-screed copper piping for my radiators has developed a leak. It's not worth digging up and repairing, because of the condition of the pipes, and the fact it's a one-pipe layout.

As much as I'd love to retrofit UFH, there isn't sufficient depth available, which leaves radiators, and there are two main options:
1) Traditional trunk running through the loft, coming down the walls to radiators, each with TRVs.
2) Centrally-located manifold with electric actuators, controlled by remote thermostats in rooms. No TRVs on radiators.

In both cases, any in-room pipes would be surface-mounted and boxed in, vertical drops behind MDF boxing in the corner of the rooms, horizontal runs behind skirting.

Is a manifold/actuator-type system overkill in a small property (approx 100m^2, single-storey)? The thing I like about it is:
1) each thermostat will be away from the radiator, so gives a more accurate room temperature.
2) multiple radiators in a room can be controlled together.
3) when the room doesn't require heat, the relevant pipes won't be circulating and thus wasting energy.
4) the potentially noisy moving part is in the utility room or loft, rather than on the radiator as with TRVs.

Biggest downside I see is that there is more pipe (and hence water to heat, when all rooms are calling for heat) overall, since each radiator gets a dedicated feed and return pipe.

With a manifold system, you could potentially run PEX all the way from the manifold directly to a radiator, without any joins. I don't see how that approach could work in a retrofit with solid floors and walls, because of the minimum bend radius of the PEX. A 10cm radius is already the height of skirting boards. It seems the logical approach is to use copper below the radiators for the last leg (or maybe down the walls too). By that stage, you may as well swallow the cost to run copper through the loft too and solder the entire lot.

Other than the leaking and inefficiency of one-pipe, the existing system was very loud with expansion noises (mainly the pipes themselves expanding in the screed), so the replacement system needs to be as quiet as possible. The best way to do this seems to be to lag all pipes, and tie-down over the lagging, rather than by clamping directly to the pipes. I'm concerned about how noise-reduction fits in with air-tightness through ceiling penetrations. One option is to accept a bit of extra bulk in the pipes running down the wall, and wrap them with some thin Armaflex sleeve/lagging as they pass through the ceiling (as they will be with the thicker insulation in the loft itself), and re-seal the hole up to the lagging.

Any advice/input greatly appreciated.

Have you thought about installing an air-to-air heat pump instead?
It will probably cost a bit more but might be worth considering.

Thanks for your replies!

Posted By: Peter_in_HungaryIMO the choice between manifold or traditional piping probably is largely influenced by the location of the boiler to the rest of the house.

That's a good point. The boiler is at the back of the property. The utility room runs to the middle of the longest side of the bungalow. I'll discuss with the installers and see what their thoughts are.

Heat loss from heating pipes is not a real loss because it is going into the heated envelope albeit perhaps not exactly where you want it. (caveat pipes in the loft have to be under the loft insulation) PEX has lower heat loss than copper.

Agreed. This is another reason I like the idea of a central manifold and actuators, since any un-insulated (or minimally insulated) pipes will only be giving off "unwanted" heat in the room that they're destined to heat. The loft runs would have thick pipe insulation, in addition to being under the loft insulation.

Posted By: derekeHave you thought about installing an air-to-air heat pump instead?
It will probably cost a bit more but might be worth considering.

That thought has been in the back of my mind for a couple of years. I like the idea of ducted air, and it could be easily retrofitted in a bungalow. The thing that puts me off is experience working in offices with warm air blowing out the ceiling, it doesn't seem to give as even a heat distribution throughout the room as radiators or UFH.

Posted By: Mike1

Posted By: CX23882As much as I'd love to retrofit UFH, there isn't sufficient depth available

Not even 15mm?
https://www.nu-heat.co.uk/underfloor-heating/renovations/lopro10/

I've looked at those and similar systems. The main thing that puts me off is that I have no insulation in the floor. I've read comments, can't recall where, that fitting just 25mm of insulation isn't perfect but puts you in a much better position than no insulation, but it doesn't leave enough depth for a wet screed. Going for something like plywood over the top seems like it would lose some of the benefits of UFH (thermal mass of the screed).

I eventually bit the bullet and settled on a replacement system using a traditional layout of 22mm trunk with 15mm branches in soldered copper, and had it professionally installed.

I used Stelrad STARS to design the radiator sizes, designing for mean water temperature of 50degC flow, -3degC OAT, 19degC IAT, a mix of air-changes based on room type, and taking a slightly conservative estimate of insulation (since I don't KNOW how well the cavity wall insulation was installed, but I know that the large UPVC windows are nearly 30 years old). It's a nice tool - free to use, but although I spent some time entering all the details, it wasn't that far off my initial rough "fag packet" calcs.

The old system was comprised of single panel non-convectors. The replacements are all Stelrad compacts (mostly horizontal, and some verticals), type 22 (except one type 33), and in most cases slightly wider than the old ones. I kept the original boiler, which is a condensing combi. Basic Honeywell stat for now, and Danfoss TRVs. I stuck with the tradition of placing them under windows.

The result: even on a -2degC morning, 40degC flow is more than good enough (and this was before loft insulation was re-laid following the installation). There is no visible pluming from the boiler flue (used to be clouds of it), and the boiler runs at a steady modulated rate rather than cycling as it would do before (at 75-80degC!). The panel surface temperature is so low that I have had to get out the IR camera to tell that they are actually have water flowing through them.

Comfort is so much better - everything is just evenly warm, without any hot spots or drafts. The system is able to raise from overnight setback to daytime temperature within 30 minutes, whereas it would previously take hours to raise even a couple of degrees. Literally every aspect of the system is better with properly sized radiators, and correct piping.

I need to collect some longer-term data, but a quick spot-check of gas kWh usage for days with equivalent conditions (day of week, UV and temperature) shows that gas consumption is in worst-case HALF what it was, but in more cases, a THIRD! I wonder how many more UK buildings are equally as wasteful!

Posted By: djhSomething sounds a bit off there. Unless you have unusually insensitive hands, you should be able to feel 40°C as pretty hot and even 30°C as warm. What temperature does the IR camera say the radiators are at? And the input pipes to the radiators?

The flow side and top get to 32degC for the first few minutes after startup, eventually reaching around 38-39degC.

Naturally I can feel the higher temperature. But it is so subtle that you cannot tell by touch whether it's residual heat due to the heating being "previously" on, or if it is "currently" on, hence the need to visualise the temperature difference. With high temperature, it is very clear when hot water is flowing through through a brief touch.

Posted By: CX23882The result: even on a -2degC morning, 40degC flow is more than good enough (and this was before loft insulation was re-laid following the installation)...............Comfort is so much better - everything is just evenly warm, without any hot spots or drafts. ................The system is able to raise from overnight setback to daytime temperature within 30 minutes,I need to collect some longer-term data, but a quick spot-check of gas kWh usage for days with equivalent conditions (day of week, UV and temperature) shows that gas consumption is in worst-case HALF what it was, but in more cases, a THIRD!

So the improvements and efficiencies came from over sizing (from conventional calculations) the radiators to allow a very low flow temperature - correct?