Bypass radiators waste money?

RainTown

Hi

my hunch is my “bypass radiator” is wasting money. Am I right on this, and if so what should I do about it?

My combo boiler circulates thru 7 radiators. 

6 have  Hive TRVs on them, one in each room of the flat. 

The seventh is in my (relatively large) hall, right opposite my main front door.

for reasons not relevant here, when the home is in use it’s often just 1/2 people using at most a couple of rooms. This will be same for the foreseeable future. 

When eg I’m in my living rooms watching TV I  really want JUST to heat that room, maybe also the toilet to lower temp. 

But what actually happens is my hall bypass radiator gets as hot, sometimes hotter,  than the others, as it implicitly tries to heat the hall while the living room heats up too.

I’d  like to fit a TRV on hall radiator too, but to my understanding I need leave one radiator “always open”  OR get engineer to fit an auto bypass valve near my boiler. 

Knowing what I know now, I tend towards doing the auto bypass valve thing. 

Is my logic sound?  Other options. 

Thanks in advance … 

HHarry

Which room is the thermostat in?  If it’s in the hall then your idea wouldn’t work, because the TRV would shut the hall radiator off, but the thermostat would stay on and the boiler would be constantly on with water running through the (new) bypass.  Probably wasting less energy that heating the hall, but still a waste.

You could move the thermostat to the room that you most often want to control the temp in (Living room), take that TRV off and put it onto the hall radiator.  Or you could have a wireless thermostat which you could move as necessary (having to rememeber to turn the TRV up in that room).  Or there are all sorts of smart TRV’s which can be used to give very specific control.

ThisIsWeird

As HH says.
One rad will effectively act as a by-pass, as one should also be the non-TRV'd rad where the Hive is located. And that room should be the most important room to heat - Ie your sitting room.
So, move that Smart TRV from the sitting room rad to the hallway rad, and set the hallway temp to whatever you want it to be - say just 15oC to keep the chill away, or even fully off if you want.
The sitting room rads should be 'manual', Ie constantly open, and the Hive moved to there (if it isn't already). That room's temp will then be controlled - and far more accurately and comfortably - by the Hive itself.
All other rads controlled by the App.

There are two ways to control Smart TRVs using the Hive. One is to have each TRV having completely independent control over the boiler. So, if Bed2 TRV calls for heat, it not only 'opens' but also turns on the boiler as required. This is the best form of control, as it doesn't require the boiler to already be on. The wee drawback to this is if you have some rads without Smarts on them - these will also be supplied whenever the boiler comes on. 
The other method is having just the Hive stat controlling the boiler, so it would have to be 'calling for heat' before any other rad has a chance of a supply ie, like most CH systems. With this, if Smart Bed2 TRV calls for heat, it won't also turn on the boiler, so will only get heat if it happens that the boiler was already on providing for the sitting room. That makes sense?

So, make the Hive-located room your 'by-pass' rad room, and make that your sitting room

RainTown

Hi

thanks for the interesting comments and observations 

The topic is really about cost rather than comfort, at least that’s my driver.

If gas was free, and using too much was not bad for environment, I wouldn’t ask !!

But really I don’t understand some of the logic. 

From my point of view, the thermostat (which is movable hive one, therefore can go in any room, right now is in the hall) seems almost redundant.  I can set individual  target in every room in house on their respective radiator TRVs via Hive app, why do I really need a thermostat at all? For now I’ve just set the thermostat to a low temp, much lower than current temp.

My best approaches seem to be:

A: Add hive TRV to hall radiator, so that all rads have one , and get gas engineer to add an automatic bypass valve into the flow near the boiler to avoid risking damage to boiler (pumping against a potentially completely closed system)

B: Move Hive TRV from bathroom rad to Hall rad, make bathroom rad the bypass, put thermostat in bathroom with low target temp. Then any time I’m heating any other room, bathroom gets
 heated too. 

Or I’m completely missing something critical!

by the way, it could be also that my Hall radiator is maybe “too open” for its purpose, cos it also gets hotter quicker than any other radiator. 

FreeBear

RainTown said: My best approaches seem to be:

A: Add hive TRV to hall radiator, so that all rads have one , and get gas engineer to add an automatic bypass valve into the flow near the boiler to avoid risking damage to boiler (pumping against a potentially completely closed system)

B: Move Hive TRV from bathroom rad to Hall rad, make bathroom rad the bypass, put thermostat in bathroom with low target temp. Then any time I’m heating any other room, bathroom gets
 heated too. 

Or I’m completely missing something critical!

by the way, it could be also that my Hall radiator is maybe “too open” for its purpose, cos it also gets hotter quicker than any other radiator. 

Some boilers come fitted with an internal bypass valve - Have a read through of the installation manual for your make/model/year of boiler.

Traditionally, thermostats were fixed to the wall in the hallway, and the nearest radiator was not fitted with a TRV. In addition, the bathroom radiator wasn't fitted with a TRV, so acted as a bypass & also a heat dump for heat only boilers that didn't have zone valves or modern controls (e.g. Parkrays & Baxi Bermudas from the 1970/80s). With more modern boilers, there is still a tendency to nominate the bathroom radiator as a bypass.

If your hallway radiator is getting hotter faster than the others, that suggests the balance is off. Could be worthwhile getting a pair of clip on thermometers and checking/tweaking the lockshield valves. To balance a central heating system effectively takes time, and most plumbers/engineers are not willing to hang around long enough to do a proper job (probably because the customer isn't willing to pay for the extra time).

RainTown

Thanks Freebear. 

the baxi 400 series does not seem to have an internal bypass valve to me, but I’ll check that with their support tomorrow. 

I’m certain it’s not going to be brilliantly balanced as installation engineers for boiler just left once verifying everything “worked”.  Next job was an emergency 😉

I’m patient and determined and motivated. If there’s a good link /tutorial for executing balancing procedure , please share. 

Incidentally, you didn’t criticise my options A and/or B as being somehow mad. Can I presume they are sensible ideas ? 

ThisIsWeird

RainTown said:

Hi

thanks for the interesting comments and observations 

The topic is really about cost rather than comfort, at least that’s my driver.

If gas was free, and using too much was not bad for environment, I wouldn’t ask !!

But really I don’t understand some of the logic. 

From my point of view, the thermostat (which is movable hive one, therefore can go in any room, right now is in the hall) seems almost redundant.  I can set individual  target in every room in house on their respective radiator TRVs via Hive app, why do I really need a thermostat at all? For now I’ve just set the thermostat to a low temp, much lower than current temp.

My best approaches seem to be:

A: Add hive TRV to hall radiator, so that all rads have one , and get gas engineer to add an automatic bypass valve into the flow near the boiler to avoid risking damage to boiler (pumping against a potentially completely closed system)

B: Move Hive TRV from bathroom rad to Hall rad, make bathroom rad the bypass, put thermostat in bathroom with low target temp. Then any time I’m heating any other room, bathroom gets
 heated too. 

Or I’m completely missing something critical!

by the way, it could be also that my Hall radiator is maybe “too open” for its purpose, cos it also gets hotter quicker than any other radiator. 

You seem to have a good handle on this :-)

As FreeBear says, if the 'issue' is that your hallway rad is heating up the hallway waaaay faster than the rest of the house, then - yes - the hallway rad is too 'open' for its space. Ie, your house isn't 'balanced'.

But, the solution in your case - since you have Smart TRVs on all rads but one - is obvious. Make the non-SmartTRV room rad the 'Hive' one. And set you Hive to give each Smart TRV control over the boiler. Ie, each individual rad can 'call' for heat whenever it needs it. Meanwhile, you always have one rad - the Hive-roomed one - 'open', so acts as a by-pass should the boiler actually need it.

I would hazard that a HiveStat-controlled room will always be more temp-stable than even a Smart TRV one, as it detects the actual room temp at a height where the humans also detect it, whereas TRVs will be at ground level, and susceptible to the actual rad's output - it's right beside it, after all. I also suspect that Smart TRVs have a greater built-in hysteresis so they don't keep reacting 'noisily', because that 'whirrrr' is quite annoying. My wife says.

So, for best efficiency, surely the 'best' and most accurate control is best, too? Ie, the main room Hive-controlled, and all other rooms TRV'd.

theoretica

RainTown said:

From my point of view, the thermostat (which is movable hive one, therefore can go in any room, right now is in the hall) seems almost redundant.  I can set individual  target in every room in house on their respective radiator TRVs via Hive app, why do I really need a thermostat at all? For now I’ve just set the thermostat to a low temp, much lower than current temp.

My thermostat is what tells the boiler to turn on or off - my TRVs only shut off or open an individual radiator.  If you only have TRVs would you then have the boiler pump on all the time just circulating hot water around the pipes (which wouldn't be 100% efficient and so cost money).  Maybe your smart system the TRVs can turn the boiler on and off, but mine can't.

ThisIsWeird

theoretica said:

RainTown said:

From my point of view, the thermostat (which is movable hive one, therefore can go in any room, right now is in the hall) seems almost redundant.  I can set individual  target in every room in house on their respective radiator TRVs via Hive app, why do I really need a thermostat at all? For now I’ve just set the thermostat to a low temp, much lower than current temp.

My thermostat is what tells the boiler to turn on or off - my TRVs only shut off or open an individual radiator.  If you only have TRVs would you then have the boiler pump on all the time just circulating hot water around the pipes (which wouldn't be 100% efficient and so cost money).  Maybe your smart system the TRVs can turn the boiler on and off, but mine can't.

The Hive's Smart TRVs has both option - either to just open and close according to the set instructions in the App, or to also turn the boiler on when asked.

Since I have only one Smart TRV, all it does it open the rad at the time required, to the temp required. It then requires to have the boiler already running for it to receive CH water. Very often - say when we have a fire going in the sitting room - the boiler is off, so the bedroom rad is cold...

The reason I don't have the bedroom TRV set to also turn on the boiler is that I don't want the other manual rads in the house coming on at the same time.

Since RainTown has a Smart TRV on every rad (apart from the Hive-roomed one), I'd have them set to demand the boiler come on whenever they 'call'.

RainTown

Thanks again for all answers 

Yes, all my smart TRVs can turn the boiler on “calling for heat” according to their target vs current temp, schedule, etc. 

And in my case those TRVs are at the top of the radiators, approx waist height. And yes again, the hive thermostat can be put to any location & height on a wall mount and is likely more accurate. 

I’m still minded to move the smart TRV from bathroom to hall, and make the bathroom rad the bypass one. For my use case, which might be unusual:

Heat bathroom + other room(s)

feels wayyyy more sensible  than

Heat hall + other room(s)

Hall is likely 5x the area of the bathroom. And I only walk through the hall area, I rarely stay there long !! 

ThisIsWeird

What do you have in the sitting room? Smart TRV? If so, why not move that into the hallway? That'll make every room individually regulated, and the by-pass one the sitting room's, where the Hive should be?
What am I missing!