Looking for advice on setting up bypass radiators
I was wondering what an efficient way of setting up bypass radiators is?
Firstly what is the difference in setting up a radiator to act as a bypass in these different ways?
1) No SRV fitted, just set to be open (TRV removed)
2) SRV (set to, say, 25 degrees) , but set to be 'independent' from zone controller
3) Standard TRV left to, say, '5' on a scale of 1-6.
I have 2 bathroom towel radiators that dont have an SRV, just always set to low.
Then I have a hallway and kitchen (both on SRV) that I dont really care what temp they hit, should these 2 be set to independent and 25 degrees? Or would this steal heat when its being called for elsewhere?
I was readinf @eezytiger comments on this thread:
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Since you referenced my post I will offer a reply, but with the caveat that I am a layman in heating systems and have only been building my knowledge since installing Tado last October.
A bypass radiator is only required if you do not have a bypass valve already built into the pipework or integrated within the boiler. Its purpose is to make sure that water can still flow during pump overrun when all radiators are shut down via TRVs/SRTs/manually. My boiler - Vaillant Ecotec Plus 831 - has an integrated bypass within the boiler and the installation instructions state that TRVs/SRTs may be fitted to all radiators.
Currently I do have a bypass radiator (in the hall with the "main" thermostat) due to legacy installation of the heating system 34 years ago. I have only recently come to realise that, with my current boiler, I could actually fit an SRV to this radiator to complete the set, and that is my plan.
So, first question - do you need a bypass radiator on your system at all?
Assuming you do, then in my opinion it makes most sense to locate it where the heat will be most useful - probably the bathroom, since extra warmth is always appreciated there. But remember that the job of the bypass is to allow water to continue flowing, not specifically to gobble up and spit out every last drop of heat produced by the boiler.
With that in mind, the towel rail would be a great choice. Not only will it permit ongoing flow of water, but it won't actually take a lot of heat out of the system. If you want the bathroom warmer anyway than add the bathroom rad as another bypass for good measure.
However, I would encourage you to pay attention to balancing the system, including your chosen bypass rad(s). If you leave them wide open then they will short circuit the flow from other radiators and raise your return temperatures at the boiler too quickly.
As for fitting TRVs/SRTs to your bypass rad(s), the rad(s) need to remain open, even if only partially, so sticking £50 of SRT onto each, only to set it wide open at 25C or risking shutdown at lower temperature settings seems entirely pointless. Just use the lockshields to fine tune the balance. In other words, your first option makes most sense to me, where's options 2 and 3 make none.
So that's bypass requirements dealt with, I hope. As for your closing remarks about SRTs in the hall and kitchen, why have SRTs fitted if you don't care what the temperature is? My advice is that you should care, set sensible target temperatures and, yes, save some heat to go elsewhere in the property if that's where it's needed. The whole point of these fancy gizmos is to combine comfort with cost control. If you just set them to 25C is there any point in having them fitted - unless there are times when you want them shut down totally, but then they would make a poor choice for bypass.
Hopefully that all makes sense and I haven't offended. If I've screwed up then I'm sure someone will be along to correct me. 😉
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An efficient way is not to use a radiator as a bypass. You should get a special bypass valve installed in the system, which is a pressure controlled valve installed between the lines.
That being said, the most efficient would be when Tado modified the software of the thermostatic valves to reduce the need for such a bypass. That is, never shut all the valves at the same time.
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@eezytiger Thanks very much for your input here. I'll try to answer here:
"A bypass radiator is only required if you do not have a bypass valve already built into the pipework or integrated within the boiler. So, first question - do you need a bypass radiator on your system at all?"
My thoughts here are that I don't have one built in based on page 47 of the technical manual for the Vitodens 100-W B1KF (assuming this is the bypass valve that's relevant!)
Would fitting this have any negative impacts on the efficiency of the system, or is it always a good idea?
"In other words, your first option makes most sense to me, where's options 2 and 3 make none."
What I'm unclear about here (due to my extreme lack of plumbing knowledge!) is whats the difference in how the valve is opened for the purpose of a bypass as long as its open? As long as its not actively calling for heat, where is the issue with an SRV on it so I can adjust how 'open' it is? Which brings me back to where I dont understand how a bypass rad doesnt 'steal' more heat than is needed? Am I wasting energy having these towel rails always on low?
"As for your closing remarks about SRTs in the hall and kitchen, why have SRTs fitted if you don't care what the temperature is?"
In my mind, a bypass was acting as an overflow, so if there was too much heat? in the system it had somewhere to go. So I thought as it wasnt calling for heat (as those SRVs could be set to independent), it would just output the excess?
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Replying in reverse order from your reply....
A bypass radiator (or bypass valve) is not there to dump excess heat. It is there to dump excess water when the pump continues to pump (pump overrun) after all radiators are closed. Otherwise the pump is pumping against a brick wall and will suffer an accelerated end of life. The water needs an escape route when the radiators close all the roads.
Now, regarding using a TRV/SRT on your bypass radiator, what is the point? It costs more than a wheelhead/lockshield valve, especially if Tado is your SRT of choice. And, remembering that the concern is about flow of water, not dispersal of heat, the valve MUST remain open. So how do you guarantee that it does not close? Either you use a manual control or, if you use a TRV/SRT, you must force it to remain open by setting it to 25C and hoping the room never reaches that temperature. So it's not functioning as a thermostat control at all. £50 wasted.
Finally, I see that the bypass is optional for your boiler. Do you actually know whether it is fitted already or not? Maybe it is. Anyway, either have one fitted if you don't have it, or have an external bypass plumbed in, or take your pick of thoughtfully selected radiator to perform bypass duties without further expense. In the bathroom I really don't think it would be such a great loss because people always like a little extra heat there. The towel rail would be a good choice IMHO. But remember to balance the system.
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@eezytiger Thanks for all the helpful feedback.
So during the times when other (SRV) rooms request heat, is it the case that the bypass radiators just act as normal and will heat as long as others are calling for heat? And I'd just set the manual valve to determine whether I want that to be a little or a lot?
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Yes, exactly. Just make sure not to turn it fully off.
Fully open would also be unwise, because it would short circuit the hot flow straight back into the return, without any resistance, raising the return temp at the boiler too quickly and reducing boiler efficiency. That's why it needs to balanced with the rest of the system by adjustment of the lockshield to limit the flow rate through the rad. Maybe it is balanced already. I'm just cautioning to make sure it's taken care of.
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