Hi,
Short Summary
Long post with full background coming: but basically, we have a combi boiler and looking to move to a system boiler with an unvented cylinder. We have been exploring options for boilers and controls and getting a bit lost in what's 'best' out of the various options e.g. traditional zoned systems; weather compensated systems; opentherm; etc. I would appreciated any tips, advice or recommended reading materials please.
Background
I live in an Edwardian 6-bedroom mid-terrace townhouse which is around 2000 sq. ft. It's a sandstone construction and has modern sash-and-case double glazing throughout. In 2020, we converted the loft space and so there's lots of new insulation around now in the flooring and loft space. We use around 18,000 kWh of gas per year to heat the property.
Historically, the house had an old tank-based central heating system, but this was removed by the previous owners in 2012 when the home was fitted with a new 28KW Potterton combi boiler in the kitchen. At this time, the whole house was also re-plumbed in 22mm copper (insulated) and all rooms had large new steel 'K2' radiators fitted.
We have a number of issues with the current system:
* We suspect that the 28KW combi boiler may be underpowered for the home. I need to do the radiator BTU calculations, but there's around 15 large radiators in the house and we suspect that the boiler struggles to heat them all at the same time.
* When we run a tap, the hot water isn't instantaneous. You run the tap, the combi fires on, and then you wait 15-20 seconds for the hot water to come through - which is annoying. We currently have 3 bathrooms (1 WC only downstairs; 1 Master bathroom with bath and electric shower; 1 Attic shower room with mixer shower), but hope to swap the electric shower for another mixer when we next renovate the master bathroom - so we are sure that we wish to move to a system boiler and unvented cylinder for our next heating system.
* The whole system is run on a single zone with a single thermostat located in the ground floor hallway. We upgraded this to a Nest thermostat in 2020, which we like using, but we feel that the main central spine of the home (where the thermostat lives) can reach temperature causing the boiler to turn off, meanwhile other edge areas of the home can feel chillier.
* We are about to renovate/extend our kitchen in the next 5 years so would like to move the combi boiler away from our kitchen. It currently has a horizontal flue venting out to our back garden. We've got loads of spare loft space would ideally like to locate a new system boiler and cylinder into the loft space - and have a vertical boiler flue venting out of our roof.
What we had been considering
* Rip out existing combi boiler from kitchen
* Mains gas into our property (believe) is currently run in 15mm copper. We would rip this out and re-run in 28mm copper. This new pipe would be run to the loft space (where we want the new boiler to be located) with a spur to the kitchen for the existing gas hob. We would also replace existing plastic mains cold water line at the same time (upgrading it to 28mm copper) feeding up to the loft space and into the combination valve - for balanced cold water
* Get a new Viessmann 200-W 35KW system boiler and fit in the loft space
* Get a new Telford Tempest Indirect Unvented Cylinder (250 litres) and fit in the loft space next to new boiler
* Plumb it in using a 4-pipe based approach (separate connections to boiler for cylinder and heating circuits)
* Run various new sets of 22mm copper from the loft to join the existing CH Flow and CH Return pipes and to provide HW flow (and balanced cold) from new cylinder to the 3 bathrooms and kitchen sink
* Connect existing Nest thermostat location up to the new boiler in the loft (using Opentherm)
Issues
* It appears like the Viessmann 200-W does not support OpenTherm
* It appears like the Viessmann 200-W favours its own 'Weather Compensation' mode in conjunction with Viessman controls
* I could 'downgrade' to the Viessmann 100-W, which DOES support Opentherm, but I unclear which is better (i.e. Viessmann WC mode vs. Opentherm). I understand the principles of both, but I do not understand which is seen as optimal.
* In either case, I am still with a 1-zone system, so I am unclear how this new system would sort the problems of the 'core' of the house getting hotter quicker than the some of the edge rooms. At one point I debated whether we should add some 3 or 4 zone valves to the system (for the 'rear extension' area of the home; for the 'main' central area of the home; and for 'loft conversion' area of the home), but I am not clear how a multi-zone system works in conjunction with Weather Compensation mode.
Sorry - a big long post. Thanks in advance for reading and I appreciate any tips or suggestions you can offer me.
Short Summary
Long post with full background coming: but basically, we have a combi boiler and looking to move to a system boiler with an unvented cylinder. We have been exploring options for boilers and controls and getting a bit lost in what's 'best' out of the various options e.g. traditional zoned systems; weather compensated systems; opentherm; etc. I would appreciated any tips, advice or recommended reading materials please.
Background
I live in an Edwardian 6-bedroom mid-terrace townhouse which is around 2000 sq. ft. It's a sandstone construction and has modern sash-and-case double glazing throughout. In 2020, we converted the loft space and so there's lots of new insulation around now in the flooring and loft space. We use around 18,000 kWh of gas per year to heat the property.
Historically, the house had an old tank-based central heating system, but this was removed by the previous owners in 2012 when the home was fitted with a new 28KW Potterton combi boiler in the kitchen. At this time, the whole house was also re-plumbed in 22mm copper (insulated) and all rooms had large new steel 'K2' radiators fitted.
We have a number of issues with the current system:
* We suspect that the 28KW combi boiler may be underpowered for the home. I need to do the radiator BTU calculations, but there's around 15 large radiators in the house and we suspect that the boiler struggles to heat them all at the same time.
* When we run a tap, the hot water isn't instantaneous. You run the tap, the combi fires on, and then you wait 15-20 seconds for the hot water to come through - which is annoying. We currently have 3 bathrooms (1 WC only downstairs; 1 Master bathroom with bath and electric shower; 1 Attic shower room with mixer shower), but hope to swap the electric shower for another mixer when we next renovate the master bathroom - so we are sure that we wish to move to a system boiler and unvented cylinder for our next heating system.
* The whole system is run on a single zone with a single thermostat located in the ground floor hallway. We upgraded this to a Nest thermostat in 2020, which we like using, but we feel that the main central spine of the home (where the thermostat lives) can reach temperature causing the boiler to turn off, meanwhile other edge areas of the home can feel chillier.
* We are about to renovate/extend our kitchen in the next 5 years so would like to move the combi boiler away from our kitchen. It currently has a horizontal flue venting out to our back garden. We've got loads of spare loft space would ideally like to locate a new system boiler and cylinder into the loft space - and have a vertical boiler flue venting out of our roof.
What we had been considering
* Rip out existing combi boiler from kitchen
* Mains gas into our property (believe) is currently run in 15mm copper. We would rip this out and re-run in 28mm copper. This new pipe would be run to the loft space (where we want the new boiler to be located) with a spur to the kitchen for the existing gas hob. We would also replace existing plastic mains cold water line at the same time (upgrading it to 28mm copper) feeding up to the loft space and into the combination valve - for balanced cold water
* Get a new Viessmann 200-W 35KW system boiler and fit in the loft space
* Get a new Telford Tempest Indirect Unvented Cylinder (250 litres) and fit in the loft space next to new boiler
* Plumb it in using a 4-pipe based approach (separate connections to boiler for cylinder and heating circuits)
* Run various new sets of 22mm copper from the loft to join the existing CH Flow and CH Return pipes and to provide HW flow (and balanced cold) from new cylinder to the 3 bathrooms and kitchen sink
* Connect existing Nest thermostat location up to the new boiler in the loft (using Opentherm)
Issues
* It appears like the Viessmann 200-W does not support OpenTherm
* It appears like the Viessmann 200-W favours its own 'Weather Compensation' mode in conjunction with Viessman controls
* I could 'downgrade' to the Viessmann 100-W, which DOES support Opentherm, but I unclear which is better (i.e. Viessmann WC mode vs. Opentherm). I understand the principles of both, but I do not understand which is seen as optimal.
* In either case, I am still with a 1-zone system, so I am unclear how this new system would sort the problems of the 'core' of the house getting hotter quicker than the some of the edge rooms. At one point I debated whether we should add some 3 or 4 zone valves to the system (for the 'rear extension' area of the home; for the 'main' central area of the home; and for 'loft conversion' area of the home), but I am not clear how a multi-zone system works in conjunction with Weather Compensation mode.
Sorry - a big long post. Thanks in advance for reading and I appreciate any tips or suggestions you can offer me.
