Appropriate temperature for sun lounge.

[megger]

Hello, I am seeking advice how to improve/maintain around 22 centigrade in my sun lounge. Room size is 3.5x4.5x3m high. 3 external walls brick cavity insulated. Double glazed glass area is approx 8sq metres. 30 degree lean to concrete tile roof with 100mm insulation board. Currently heated with 2xK1 type rads giving a kw output of 0.75 kw each. Piped in series on 8mm microbore and 9 metre run to manifold.
In series because where the sun lounge connects with the main lounge there is already a rad and one close by in the dining area. I also piped those in series on the existing 8mm m/b that fed the dining rad. I added the 2x0.75 kw rads 8 year ago when my 29 year old 14kw Thorn olympic boiler was still going strong. 2015 the old Thorn cracked so was replaced with a 26kw system boiler but still using the 22mm to manifold to 8mm microbore with the same rads throughout.
The 26kw boiler heats the rads up much quicker but as we know the likes of conservatories and sun lounges can have heating needs quite different to the main building. Most of the rads are controlled by TVR's, with the temp stat sited in the hall which keeps the house comfortable but not the sun lounge.
I realize the 2x0.75 rads are under the room requirement. A recent re- calculation tells me I should have at least 2x1.4kw rads instead which in itself is not a problem to change. It's getting the control to keep the room warm say 19 to 21 C because once the hall stat is happy it is too long a time span before it demands heat again by which time the sun lounge has become cold.
So to improve things without re-plumbing (and you'll likely tell me I'm asking for the moon on a stick here) would be to fit 2x1.4kw rads. But also to replace all the existing TVR's with programmable ones. From what I understand these appear to be more sensitive to temperature requirements and improve comfort overall?
Or pull up the floorboards and run in a 15mm from the 22mm to the sun lounge. From the loft where the boiler is now is about 14 metres. Then I would wire in another stat for the sun lounge, fit another c/h zone valve in the loft so the room has it's independant temp control then. And re-connect the lounge and dining rads back to how they were originally.
Any ideas will be greatly appreciated.

 

[muggles]

Wow, your query raises so many questions it's genuinely difficult to know where to start!

Is your roof insulation covering the joists, or just between? An additional layer underneath the existing ceiling would improve things a lot either way, but especially so if your insulation is only between the joists as you'll get thermal bridging through the timbers.

Piping radiators in series is never a good idea (are you sure you don't mean in parallel?) but especially on 8mm which should always be run back to the manifold or 22mm primaries. Anything other than re-piping things correctly will be a sticking plaster.

Putting Evohome or similar in will improve control, but will also be expensive. What's your aim in doing this?

I have to wonder why a 14kW boiler was replaced with a 26kW boiler. Did your house double in size?

Independent time and temperature control of your sun room certainly wouldn't be a bad idea, and a zone valve with its own pipework would be a good way of achieving that

 

[megger]

Hi muggles, thanks for your interest. The insulation is Kingspan and is 150mm thick, not 100mm. But it is between the joists. I might have to put up with any thermal bridging as it would be a major job to alter the ceiling for additional insulation.
I piped the rads in series as I learned if you tee them in parallel you can't get a balance when fed on 8mm. However the second rad takes longer to heat but does get hot, but not ideal as you say.
I bought the house new in 1980 a 3 bed detached that came with a Thorn olympic 14kw boiler, gavity fed elson hot water tank and pumped c/h to 9 rads. I soon found out the builders threw in a cheep system where I had to increase size of some rads. Then later I built on and put more load on the boiler and had to constantly use the electric immersion to get the water hot.
I raised the issue to change the TVR's to digital as sometimes I'm in doubt as to whether they control as they should?. I have 1 TVR fitted to only one of the rads in the sun lounge with them been connected in series. With TVR set at 3.5 and you get a warmer outside temperature with the sun shining in, it appears to remain open wasting boiler energy. Iv'e tried changing it for another one as well. I was hoping to get other peoples judgement to say they found digital TVR's to control as you'd expect.
I notice you are twisting my arm to re-pipe and control the room temp separately which I must agree and bite the bullet.
I hope Iv'e answered your queries and i look forward to what else you might have to share.

 

[megger]

This is a follow up to the changes I made to my c/h system where it has been well worth the effort and cost. Four weeks ago I decided to put in larger pipes and radiators and independently control the lounge and sun lounge to the main house. First I worked out the electrical control which involved a joint box two relays, two more zone valves and two programmable room temperature stats. I run 22mm flow and return from loft to ground floor then subsequently reduced to 15mm to the rads. Fit the joint box, zone valves and stat's in stairs cupboard. Fit a 1.5 kw type 11 rad in lounge (up from 0.8kw) and two 1.4 kw type 22 rads in sun lounge (up from 2x0.7 kw). I had my local plumber to do the necessary pipework in the loft,connect the new 22mm in, cap off the old 8mm microbore pipe ends, put in fresh rust inhibitor and commission the system. And I only wish I had done it years ago, what a heck of a difference it has made especially to the comfort in the sun lounge on a cold frosty night.
By having programmable stats I can now have the two rooms to warm up later on a morning as we are mainly in the kitchen and bathrooms first thing then jobbing about so I would hope to reduce the overall gas used per day.
Anyway just thought I'd let you know in case anyone else is perhaps thinking along similar lines.