Worth getting TRV for bathroom towel radiators?
I have 6 radiators with the smart TRV, plus one without it - to act as a bypass? I'm not sure if that is required, but there you go.
I'm wondering about the 2 bathroom towel radiators, currently I guess they are effectively acting as a bypass as well, but this means they pull heat when any of the others request it.
Should I get a smart TRV for those 2? Is that typical? Any downside?
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A bypass is necessary when using systems like Tado. If your towel radiators function as bypass there you have your answer.
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I have a separate one in the hallway that can act as a bypass. So maybe I should go for the SRT on the bathroom rads. It seems like the best way to avoid unnecessary heating.
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If I had to choose between uncontrolled heat in the bathroom or the hall, then I’d opt for the bathroom. The extra heat will dry your towels and reduce the amount of condensation when someone takes a shower. Assuming your hallway is just a corridor that you pass through and not somewhere to spend time.
Assuming you have your own boiler have you considered its minimum heat output. Micro zoning your rooms will give you comfort, but may not be energy efficient. For instance if your boiler has a minimum output of 4KW and the only active radiator is rated at 1KW then the mismatch will mean energy is wasted.
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Thanks for your input @GrilledCheese2
That makes a lot of sense, I think I'll follow your suggestion there and keep the bathroom ones on low without an SRV, and get an SRV fitted to the hallway one. You're right in that its just where we pass through as opposed to standing in the hall. I think a temperature sensor for this may be overkill so will probably just use the SRV for measurement there.
The boiler is a Viessmann 100-W B1KF 35kw - I'm believe its minimum is 3.2kw
So with the 2 bathroom rads being on if anything else is calling for heat, I ideally want that to be at least 3.2kw so I'm not wasting any energy? I'm not sure how to measure how much kw the bathroom rads are pushing out though?
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Viessmann boilers have one of the lowest outputs so you’re in a good position for keeping your system efficient. The easiest way to determine the KW rating for a radiator is to measure the size and find something similar online.
If the radiator load is less than the boiler output it will cause the returning water temperature to be too high, which reduces the amount of condensing in the boiler. Eventually the excess heat will cause the boiler to switch off to allow the heat exchanger to cool down. The boiler will then cycle on and off to compensate for the radiator not being able to dissipate sufficient heat. Ideally you want the returning water temperature to be as low as possible and for the boiler to run at its lowest output without cycling.
Recent comments from eezytiger illustrate what I have described above.
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Thanks for the details. So am I right in thinking that if any one of my SRVs call for heat, the boiler will push a minimum of 3.2kw out, and if I dont use that, besides being inefficient, its not really ideal for the boiler?
As one of the 2 towel radiators is this one, and it says 4.56 l/kW, does that mean I will be able to use all the heat the boiler is giving me?
Does it matter that these 2 bathrooms rads are set pretty low? I guess I'd like them just to receive excess heat, but is it the case they 'steal' heat before it can go to the SRVs that are calling for it?
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The heat output for that radiator is 379 Watts (or 0.379KW).
Mechanical components are designed to work for a number of on/off cycles, and it’s not ideal if you’re using more of those cycles than you need to. When the heating system is cold and one SRV calls for heat the boiler will initially turn on at medium or high heat and then modulate down towards the minimum heat as the flow water temperature reaches the set temperature. E.g the water heats from 20°C to 60°C and the boiler ramps down from 10KW to 3.2KW. Once the boiler is down to it’s minimum it will be unable to keep the water temperature within limits and start to short cycle. The cycling means the gas valve, ignition, flue fan and water pump are stopping and starting and that leads to additional mechanical wear. Of course the boiler is designed to switch on and off, but it helps to keep the number of cycles low.
Nothing wrong with keeping the radiators low and prioritising hot water to the SRVs.
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So would it make sense to try and have more radiators using the excess heat?
For example, I should keep the 2 bathroom rads without SRV and on low, then maybe the SRVs on the kitchen and hall (where I dont really care too much about the temp), set to independent and on about 24 degrees or something?
I'd like to make sure I'm setting this setup as efficiently as practical, whilst keeping control of the rooms I want to be able to set.
What I'm unclear about (or one of the things!) is if I have 4 SRVs asking to heat up from 18 to 21 at the same time, are the bypass rads, and possible independent rads, taking heat from the boiler that I would want prioritised to the SRV ones?
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It certainly makes sense to keep full control of the SRVs in the main living space as this will give you the best comfort. Leaving the less used rooms set to Independent mode. Don’t worry about taking heat away from the boiler. Combi boilers are usually more powerful than regular boilers; 35KW will give you plenty of heat when there is demand.
The best thing to do is to try a few options for a week or so. See what works for you and keep an eye on the gas meter readings. The outside temperature will obviously impact how much heat your home needs.
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@Floob I get the impression that you are overthinking this too much. Based on the fact that tado SRVs can call for heat in rooms that couldn’t before, I expect more energy to be used than before, unless you now can turn of heat requests in rooms that you couldn’t before (most notably the living room)
Yes, you need to make sure hot water can always flow, hence a bypass of some sort is necessary in a system with only smart valves (conventional or tado) and/or ufh. If you use a bypass valve, it must be set to a small pressure difference (factory default will suffice, most likely something like 0.2 bar) and must be sufficiently far from the boiler so return water is not too hot which would cause the boiler to cycle in short intervals.
If you have anywhere in the system a radiator that is always open, it acts as a bypass an providing heat in the room where it sits.
You can consider it a loss of heat if it is somewhere where you don’t need it to be warmed up. And it will also do this whenever hot water is flowing due to heat request from other rooms (when a bypass valve would be closed as there is no high pressure difference).
Please note that the bypass is for exceptional situations (i.e. all valves are closed, but boiler pump is still pumping). This should normally be only the case for a small % of the time and ideally not at all.
And about balancing heat produced by the boiler vs the heat demand and heat delivery capacity of the system, I don’t know much about. Most heating systems are oversized and running on high temperatures so the installer doesn’t get complaints about cold rooms etc. Somues, room for improvement there, but it is very specific to each and everyone’s system.
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@Andreplusplus "I get the impression that you are overthinking this too much"
Very possibly! I guess I'm just trying to make sure I'm not doing something daft - its such a big change from my old system.
Since I replaced my old (non-combi - with water tank) with the new boiler and Tado system, my usage has dropped a decent amount. Here is what I used with the old system that was on for 2.5 hours in the morning, and 3 hours in the evening.
Here is the last 7 days for me now, where I just have the individual rooms calling for heat when needed. I work in the living room all day and am now able to heat that suitably whilst not calling for heat in the bedrooms at the same time.
I imagine the efficiency of the new boiler is also a factor here. The old one was from 1990 (Ideal Mexico 2) and very basic - albeit reliable!
"If you have anywhere in the system a radiator that is always open, it acts as a bypass an providing heat in the room where it sits."
Yes, I currently have:
6x Radiators on SRVs, 3x Radiators on always open (slightly), these are 2x bathroom and one in hallway.
Given the hallway one gives out heat when I don't really need it I was thinking of adding an SRV to it.
I'm looking to make sure I haven't overlooked anything obvious with the setup really, I don't know anything about plumbing, and after reading this forum I feel I'm in the 'a little knowledge is a dangerous thing' category!
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Good results with that drop in energy use! Of course you need to count in outside temperature as well. And indeed I think a new boiler is a huge factor in this.
And w.r.t. your remark of little knowledge, it also a bit of common sense. And either your house is a bit too cold or a bit too hot when you do something ‘wrong’, but you won’t blow up anything or so.
And of course, people on the forum are here to help eachother and share the knowledge 😅🙂
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I’ve read a lot about bypass rads on here, My Main Eco Elite combo boiler states the below in the manual. This would suggest I have no need for a bypass rad, is that correct? Sorry to ask in your thread ;)
Bypass
1. The boiler utilises the primary side of the DHW plate heat
exchanger as an automatic integral bypass.0 -
Yes, it reads like your boiler can do without a bypass in your pipes or rads, as it has a built-in one.
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@Floob Out of interest, your kWh use looks pretty comparable to mine as you have 9 rads and are heating your living room the whole time for work. I have 11 rads, 7 with SRVs (3 bedrooms, hallway, 2 in lounge and a small office) and then have two TRVs and two bathrooms on regular valves essentially acting as my bypass rads. I use a fairly aggressive schedule to heat bedrooms in the morning but not any other time and keep the main house off when we're all out at work/school etc, but there are times when i'm working from home etc. We used 48.8 kWh on Tuesday 22nd Feb, but our normal use is more like 55-60 kWh.
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@Scale70 Yes, thats pretty close to my setup. I think my average is closer to about 70kwh, but I need to get one more rad on SRV, then leave 2 bathrooms as bypass. Here is the Feb details, x marks the new boiler.
I dont think the multiple baths are helping my stats - nothing wrong with showers! :)
Also its rare everyone is out, so I'm not really getting the advantage of geofencing.
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