Not enough Heat

[Wagger]

We have recently had oil fired central heating installed.
All radiators have TRVs. We also have a system thermostat inthe hall, set at 25 degrees.
When the heating is first switched on all radiators becomehot or very hot but our rooms and the main thermostat reach only 19/21 degrees.After around 2 hours the radiators furthest from the boiler start to cool andwhile they warm up intermittently the rooms never get above 19/21. All TRVs areset at 5.
The system has been balanced and we are satisfied that thisis not a boiler problem. Our plumber is stumped. Any ideas?

 

[Wagger]

He said after

 

[Wagger]

Yes 18 in beds Ok but 21c not comfortable enough to sit in watching telly. We aimed at 25 to get system running full bore but can not get above 21, sometimes only 19. System seems to switch off when it reaches this level even though room stat hasn't reached 25. I would have expected it to keep belting away!

 

[Worcester]

See my previous posts..

Wagger you state that ALL radiators have TRV's

Were the stat is located there shouldn't be any TRV's the system is fighting itself.

Any well designed system should be able to get a house up to 25, especially with an outside temp of 5-8, for older people that are sedentary during the afternoon we ususally set their stats to 23 for the pm (we use programmable stats so can set multiple heating levels per day)

The system should have been designed for between -1°C and -3.8°C depending upon location.

 

[Norcs]

Fit a stove.

 

[lame plumber]

if all the rads have trvs, then the rad in the hall/room with the room stat will be fighting the trv for starters. Other option, buy some jumpers.................

 

[SimonG]

Did you get your certificate from building control?

 

[NRS]

Try removing TRV heads from rooms that are cold; sounds like trv's are shutting down before your desired room temp is reached. worth a try !!

 

[gmartine]

As lame said if TRV is in hall with stat, no boiler interlock.

Completely remove TRV head in the hall and see.

 

[Davide13]

Will a TRV open on 5 start to close then? Surely it will allow maximum flow all the time or are they calibrated to close even on max.

 

[Worcester]

Will a TRV open on 5 start to close then? Surely it will allow maximum flow all the time or are they calibrated to close even on max.

They'll close even on 5 and that could well be before the room achieved temperature because they are measuring the air temp immediately adjacent to the rad, not the room temp, hence a need even with TRVs for proper balancing

 

[Davide13]

Well that's something I wasn't aware of. I'll get me coat.

 

[Best]

In the OP it was said the radiators become hot, or very hot. So if that is true it has to be undersized radiators or a faulty wall stat (or stat fitted in wrong location above a radiator for example.)
Check the entire radiator surface is fairly evenly heated.
Give us an example of details of one of the rooms that isn't getting up to heat - radiator dimensions and if single, double extra, or double convector, plus size of room including height and how many outside walls etc.

 

[Wagger]

No. Plumber can self certify certain work and the boiler was commissioned independantly by an OFTEC approved commissioner.

 

[SimonG]

No. Plumber can self certify certain work and the boiler was commissioned independantly by an OFTEC approved commissioner.

Still would receive a buiding control certificate if it was kosher.

Boiler install is notifiable now. Not the commissioning. Fitted by one person and commissioned by another. There could be the reason you have issues.

 

[Wagger]

Room dimensions in metres 2.56 high x 5.0 x 4.2. 2 outside walls 2 double glazed windows total 2 sqare meteres. Radiator double panel with single convection 600 x 1200. Stat fitted in a suitable place.

 

[doitmyself]

They'll close even on 5 and that could well be before the room achieved temperature because they are measuring the air temp immediately adjacent to the rad, not the room temp, hence a need even with TRVs for proper balancing

Most TRVs have a proportional bandwidth of about 2C, so they are full open 1C below the required temperature and fully closed 1C above.

Not knowing what temperature 5 represents (it varies according to TRV make and model), it's impossible to say if it would interact with a room stat set to 25C.

 

[Best]

Room dimensions in metres 2.56 high x 5.0 x 4.2. 2 outside walls 2 double glazed windows total 2 sqare meteres. Radiator double panel with single convection 600 x 1200. Stat fitted in a suitable place.

I haven't worked out a rough output, but that is a fairly big room. I am sure I would have put a bigger rad in. Usually a double radiator for any room approaching that size, IMO.
Depends on what type of house and how good the insulation is. Also if a bedroom or a living room, as bedrooms require less heat output.

 

[Worcester]

21m2
Very old leaky house = 2.75kw
Brand new build < 840W

Average Flow temp 55° (condensing 60 F/50 R) looking for 30° delta T = 30° Radiator factor = 0.515

Therefore output from P+ 600*1200 = 1691 * 0.515 = 870 W

Therefore rad undersized unless new build.

 

[Worcester]

Problem Solved.

That's the difference, I guess your 'installer' isn't a heating engineer. They should have done full heat loss calcs first and sized the radiators (and boiler) accordingly.

Ask to see his calcs

 

[ShaunCorbs]

Problem Solved.

That's the difference, I guess your 'installer' isn't a heating engineer. They should have done full heat loss calcs first and sized the radiators (and boiler) accordingly.

Ask to see his calcs

+1 the only way I can get the existing rad working in a normal house is to have the room temp at 21 dc

 

[Nostrum]

You 'normally' design for at 20 degree F&R TD 70-50 so a MWT of 60 which gives a 40 degree air to water delta T.

I say normally, because getting a 20 degree delta is harder than it sounds when the boilers oversized or the systems small. That's generally the industry standard on a condensing boiler though.

Worcester- your 60/50 is more feasible but leads to a lower output which can cause problems on a retro fit (keeping existing rads)

We're designing systems with a 50/40 now on gas, but it doesn't go down well even though it'd be more economic. Despite the benefits being discussed, we lose out on most gas work because the customer would rather have smaller rads and a system chucked in for half the cost.

 

[JonG1]

What boilers are you speccing Nostrum, some manufacturers flinch at the thought of their HEX running with acid 24-7?

 

[Nostrum]

ATAG (stainless hex) although as said, not won any jobs to actually fit them :wazzzup:

 

[JonG1]

ATAGs should be fine, but not sure if they are staying in the UK market, something about a takeover by Ariston?

We have done a few where we have been able to spec oversized rads, weather comp the heating or opentherm it and prioritise the HW, mostly use Intergas these days but were looking at ATAG before we started with the Gash.