Hi everyone,
I 'think' I've found a cheap solution to fulfilling all of my family's heat automation needs using Terrier i30 TRVs (eTRVs that have a timer, but no way of calling the boiler for heat). However, it seems too good to be true. Therefore, I wondered if I could run it by some of you for a sense check -- i.e. what am I missing?
I live in an old poorly insulated house with, at the present at least, no realistic opportunity to retrofit. We have two kids bedrooms that need heating early evening and two adult bedrooms that need heating later. It's too expensive to heat all for the whole evening and so I'm looking at getting eTRVs on the radiators to achieve zoned heating control for the upstairs. For info, we already have zoned heating downstairs via an underfloor system. This operates with Heatmiser room stats (are wired and can't be linked into a smart system easily).
I assume the 'correct' solution here would be to invest in a smart heating controller for the upstairs (e.g. TADO, Hive, Evohome), which would turn the boiler on/off depending on the status of a set of eTRVs. However, I'm hesitant to invest one on of these unless I have to for a few reasons:
I'm wondering whether an alternative cheaper solution might be to put Terrier i30s on all of the radiators and then run the timer for the duration they are all on. That's to say the kids' bedrooms would be on from 6-8, adults from 8-10, and heating timer from 6-10. This would be cheap, but would have a downside there being times where all eTRVs may be off and the boiler still running -- potentially causing damage by short cycling and costing unnecessary money.
I've just done a bit of a test to see what the boiler activity with all eTRVs would be like. I did this by turning all the existing manual TRVs in the house to zero and running the heating for an hour with the house thermostat on full (no hot water heating on and downstairs underfloor off). I saw the following:
These results seem to suggest that having the boiler still running in the case where all of the i30 eTRVs are off wouldn't be too much of a problem. I'd only end up paying for at most 6 minutes of oil per hour. Also if this 'wasted' heat is being directed somehow into the towel rails then this would actually be a bonus, because we don't have radiators in our bathrooms and would like them warm during the time when the bedrooms are being heated.
Therefore, it seems like i30s + our dumb timer would bring a really nice solution for our house. However, I'm worried I'm missing something important here, especially that running the system in this way would cause damage to the CH system. In particular:
1) Is a 10% duty cycle (1 minute on, 9 minutes off) considered short cycling and will it damage the boiler?
2) Is running the pump with the radiators closed for potentially extended periods at this duty cycle going to cause damage, considering there is an operating auto bypass?
A bonus of this setup (beyond my understanding why -- perhaps as a result of pressure release from the cylinder?) is that the heated towel rails seem to come on when the boiler is being called by all but the TRVs are off. We've always been frustrated with not having any control over the towel rails. The above results suggest we might be able to actually gain some control over them by intentionally running the CH timer on with eTRVs turned off (e.g. heating + TRVs on from 5-6AM, just heating 6-7 causing towel rails to come on). This seems brilliant, but again I'm worried this 'hack' is going to break stuff:
3) Is intentionally running the boiler with all of the TRVs for a short period (e.g. 30 minutes) to force water into the heated towel rails going to cause damage?
Some extra info:
I'd really appreciate your thoughts!
I 'think' I've found a cheap solution to fulfilling all of my family's heat automation needs using Terrier i30 TRVs (eTRVs that have a timer, but no way of calling the boiler for heat). However, it seems too good to be true. Therefore, I wondered if I could run it by some of you for a sense check -- i.e. what am I missing?
I live in an old poorly insulated house with, at the present at least, no realistic opportunity to retrofit. We have two kids bedrooms that need heating early evening and two adult bedrooms that need heating later. It's too expensive to heat all for the whole evening and so I'm looking at getting eTRVs on the radiators to achieve zoned heating control for the upstairs. For info, we already have zoned heating downstairs via an underfloor system. This operates with Heatmiser room stats (are wired and can't be linked into a smart system easily).
I assume the 'correct' solution here would be to invest in a smart heating controller for the upstairs (e.g. TADO, Hive, Evohome), which would turn the boiler on/off depending on the status of a set of eTRVs. However, I'm hesitant to invest one on of these unless I have to for a few reasons:
- They're expensive, we're short of cash and wanting avoid unnecessary expenses
- I'm not so interested in remote/smart features like learning/geo (had a NEST before, didn't use)
- I don't want to replace the downstairs room stats, so only the upstairs would be 'smart'.
- I'm anxious about investing in an expensive system that may not work in our house. I've read TADO doesn't have great range (we have a big house solid walls, multiple steel beams and need WiFi repeaters already) and can't be boosted. Hive is an option (does have repeaters) but I've read their eTRVs are causing a lot of people issues.
I'm wondering whether an alternative cheaper solution might be to put Terrier i30s on all of the radiators and then run the timer for the duration they are all on. That's to say the kids' bedrooms would be on from 6-8, adults from 8-10, and heating timer from 6-10. This would be cheap, but would have a downside there being times where all eTRVs may be off and the boiler still running -- potentially causing damage by short cycling and costing unnecessary money.
I've just done a bit of a test to see what the boiler activity with all eTRVs would be like. I did this by turning all the existing manual TRVs in the house to zero and running the heating for an hour with the house thermostat on full (no hot water heating on and downstairs underfloor off). I saw the following:
- After a short heat-up period the boiler ran in a cycle of one minute on and then 9 off
- The pump ran for the whole hour, with a 5 minute overrun at the end
- The auto bypass valve came into operation and was hot for what seemed like the whole hour
- The heated towel rails in bathrooms seemed to be on for the hour too
These results seem to suggest that having the boiler still running in the case where all of the i30 eTRVs are off wouldn't be too much of a problem. I'd only end up paying for at most 6 minutes of oil per hour. Also if this 'wasted' heat is being directed somehow into the towel rails then this would actually be a bonus, because we don't have radiators in our bathrooms and would like them warm during the time when the bedrooms are being heated.
Therefore, it seems like i30s + our dumb timer would bring a really nice solution for our house. However, I'm worried I'm missing something important here, especially that running the system in this way would cause damage to the CH system. In particular:
1) Is a 10% duty cycle (1 minute on, 9 minutes off) considered short cycling and will it damage the boiler?
2) Is running the pump with the radiators closed for potentially extended periods at this duty cycle going to cause damage, considering there is an operating auto bypass?
A bonus of this setup (beyond my understanding why -- perhaps as a result of pressure release from the cylinder?) is that the heated towel rails seem to come on when the boiler is being called by all but the TRVs are off. We've always been frustrated with not having any control over the towel rails. The above results suggest we might be able to actually gain some control over them by intentionally running the CH timer on with eTRVs turned off (e.g. heating + TRVs on from 5-6AM, just heating 6-7 causing towel rails to come on). This seems brilliant, but again I'm worried this 'hack' is going to break stuff:
3) Is intentionally running the boiler with all of the TRVs for a short period (e.g. 30 minutes) to force water into the heated towel rails going to cause damage?
Some extra info:
- We have an oil condenser boiler
- We have an unvented system
- There is a single thermostat upstairs, but its in a cold hall with no radiator
- All radiators already have manual TRVs, so the system should in theory have been designed to run with them all off
I'd really appreciate your thoughts!
