Radiators - Balancing vs adjusting TRV

eidolon · 28 Oct 2018 at 10:45

I have a three storey Victorian house that has just had a full new central heating system fitted. As it's an old house with quite large rooms and high ceilings I wanted to make sure that I had adequate heating so I fitted a 40kw boiler and 7000BTU column radiators throughout. Each radiator has a Drayton TRV fitted apart from the ones in the living room as I have the Nest thermostat in there so I understood that it's good practice to not have them in the same room as the thermostat. These just have normal valves on both sides of each radiator.
The boiler is at the front of the house and the kitchen/bathroom radiators are at the rear, about 15m away. This means that the living room gets really hot before the kitchen and bathroom has a chance to warm up. I've read about "balancing" the radiators but I'm confused how it differs from just adjusting the TRVs. Don't both just restrict the flow of water through the radiator?

If I want my house to heat up from the back to the front am I right in thinking that I should have the lockshield fully open on the radiators in the kitchen/bathroom, then maybe half open in the bedrooms/dining room and maybe quarter open in the living room so that the water is forced to the rear rooms first?
As I have no TRVs on my living room radiators, how do I know which valve to close? Both sides are the same.

Here's a rough pic of my layout

Tinders · 28 Oct 2018 at 11:03

General convention is Control valve on the flow side and lockshield on return.

I'd balance the rads as you would normally then just adjust the trv to suit heat demand per room.

fezster · 28 Oct 2018 at 14:21

Balance the system with the TRV's fully open (or heads taken off). This ensures all rads warm up evenly.

Then adjust TRV's as and when to individually control room temperatures (IME, nobody bothers - i certainly dont).

With regards to the boiler, fitting the largest boiler you can find is generally not advised. The boiler should be matched to the calculated heat loss of the house (though with a combi, it's usually a compromise as the HW requirement drives the boiler sizing decision). If the boiler is oversized, you can have problems with short cycling. Most modern boilers auto modulate down to a point, so you can get away with slightly oversizing.

Tinders · 28 Oct 2018 at 14:54

Isn’t it nigh on impossible to find a boiler sized for a particular house?

eidolon · 28 Oct 2018 at 16:43

Tinders said:
General convention is Control valve on the flow side and lockshield on return.

I'm starting to think something isn't right with my setup then. I have a lockshield on both sides of each of the radiators in the living room. Also, should my TRV be fitted to a particular side? I've just turned the heating on to feel which leg gets warm first and some radiators seem to have the TRV fitted to the side that gets warm first, but on others it's on the side that stays cold.

fezster said:
With regards to the boiler, fitting the largest boiler you can find is generally not advised. The boiler should be matched to the calculated heat loss of the house (though with a combi, it's usually a compromise as the HW requirement drives the boiler sizing decision). If the boiler is oversized, you can have problems with short cycling. Most modern boilers auto modulate down to a point, so you can get away with slightly oversizing.

I had three plumbers all recommend the same boiler so I'm hoping it's correct. It's quite a large old house with 3-4m ceilings throughout and solid external walls so it's not exactly an eco-home.

robj20 · 28 Oct 2018 at 16:56

If you have TRV 4 you balance using those not the lock shield. Look it up. So much easier should you ever wish to remove radiators on the future.

It's not something I did with mine as it made the system noisy, so they're all left fully open.

eidolon · 28 Oct 2018 at 19:01

robj20 said:
If you have TRV 4 you balance using those not the lock shield. Look it up. So much easier should you ever wish to remove radiators on the future.

It's not something I did with mine as it made the system noisy, so they're all left fully open.

I didn't realise that, thanks for the info.

fezster · 28 Oct 2018 at 21:05

Most TRVs can be fitted either side (eg Drayton Trv 4s), whilst some are directional and should be fitted to the flow. Your lockshield will have a removable cap (sometimes with a screw) and then a small adjustable valve inside.

fezster · 28 Oct 2018 at 21:11

Tinders said:
Isn’t it nigh on impossible to find a boiler sized for a particular house?

Not at all. Quite the opposite. Obviously, will never match exactly, but within a couple of kw is what to aim for. If you have a hot water tank, you typically programme it to come on outside of your heating times, so they don't feature in the heat calcs (most calculators add an additional 2kw for unvented cylinders, even though the coil inside will typically be rated at 20+ kw).