Underfloor heating downstairs and radiators upstairs, large Edwardian semi

[Rocket Ron]

Hello everyone
We are in the process of sympathetically renovating a large Edwardian three story semidetached house and we are considering underfloor heating for the ground floor.

 

The property benefits from double glazing and an open plan area of approximately 70 m² consisting of a lounge area plan extension with bifold windows and an kitchen separated by a single wall.

 

The property has a traditional suspended wooden floor and we are considering an overlay system such as those supplied by Wunda.

 

The materials quotation has come back as favourable however I see complications running the 35 kW valent boiler with Custom iron radiators in the upper floor and underfloor heating on the ground floor.

 

The idea for this is to reduce energy costs as well as comfort.

 

The alternative is to run cast iron radiators downstairs and upstairs at Delta 40.

 

I need some help with the best solution for our house as I have no experience within the floor heating let alone running a radiator system upstairs and an underfloor heating system downstairs. Any help and advice would be gratefully received? Is it going to be worth the cost and installation of underfloor heating over and above that of cast iron radiators. 

 

Will I be able to effectively run radiators and on the floor heating off the same boiler?

 

It’s decision time now so any help gratefully appreciated.

 

just to add that the rear of the property where the bifold windows are and the extension is has all been insulated in accordance with current building regulations the front half of the property and upstairs is traditionally built

[JohnMo]

Somethings to think about 

UFH will need a well insulated floor to perform well and at reasonable flow temps with a suspended floor, all doable but not a small amount of work. A simple overlay system will work also, but downwards heat losses could be pretty large, so may not be a cheap to run solution.

 

Boiler efficiency - this comes from boiler return temperature below 54 degs. This promotes condensation of the flue gases which increases boiler efficiency. About condensation point boiler efficiency be mid 80, get a good low low temperature your efficiency jumps to mid 90s and higher.

 

I would do a room by room heat loss, stick with radiators, design radiators to run as low a temp as practical.  Install a boiler that either runs opentherm or weather compensation. Size boiler to house heat loss, not a big one because it's a big house. Look at boiler modulation and the minimum output, the lower the min output the better. Select a boiler that does priority domestic hot water, this will then flow one temp for cylinder heating and another for central heating. Install with a heat pump cylinder, this has a massive coil, gives boiler most efficient operation and fast reheats.

 

Have one thermostat (ideally just the boiler controller), or just one battery powered opentherm one so you can move to best position. If running opentherm the boiler will be modulated based on measured temperature at the thermostat, weather compensation adjusts flow temperature based on outside temp, but a good boiler can do both at the same from the controller.

 

On radiators use a flow setter instead of TRV and set flow rate based on heat loss calculation, something like these

https://www.firepowerheating.co.uk/frv

[Rocket Ron]

1 hour ago, JohnMo said:

Somethings to think about 

UFH will need a well insulated floor to perform well and at reasonable flow temps with a suspended floor, all doable but not a small amount of work. A simple overlay system will work also, but downwards heat losses could be pretty large, so may not be a cheap to run solution.

 

Boiler efficiency - this comes from boiler return temperature below 54 degs. This promotes condensation of the flue gases which increases boiler efficiency. About condensation point boiler efficiency be mid 80, get a good low low temperature your efficiency jumps to mid 90s and higher.

 

I would do a room by room heat loss, stick with radiators, design radiators to run as low a temp as practical.  Install a boiler that either runs opentherm or weather compensation. Size boiler to house heat loss, not a big one because it's a big house. Look at boiler modulation and the minimum output, the lower the min output the better. Select a boiler that does priority domestic hot water, this will then flow one temp for cylinder heating and another for central heating. Install with a heat pump cylinder, this has a massive coil, gives boiler most efficient operation and fast reheats.

 

Have one thermostat (ideally just the boiler controller), or just one battery powered opentherm one so you can move to best position. If running opentherm the boiler will be modulated based on measured temperature at the thermostat, weather compensation adjusts flow temperature based on outside temp, but a good boiler can do both at the same from the controller.

 

On radiators use a flow setter instead of TRV and set flow rate based on heat loss calculation, something like these

https://www.firepowerheating.co.uk/frv

Thank you for the valued input. The boiler has already been installed. It is a 35 kW condensing. Vailent I’m not sure of the model number right now.

 

another thing I’d like to clarify about the suspended floors and the heat loss downwards. Are you sure that even an overlay system for underfloor heating would suffer heat loss downwards? This is contrary to what the manufacturers advice and I’m becoming confused so I came on here for independent advice.

 

I’m very much the point of making the decision and pulling the trigger and if radiators run in the way you suggest all the better option then I will continue as planned and travel around the country collecting cast iron radiators for their historical appeal and their performance

[ProDave]

How you control it is another consideration.

 

Radiators warm up quickly and warm the room quickly.  Under floor heating takes very much longer to warm up and warms the room slowly.  UFH is best operated being on for long periods at a low temperature.  So if you do the split system as a minimum you will need to be able to set different times for upstairs and downstairs heating.

 

UFH losses to the floor void can be massive without sufficient insulation.  Most recon at least 100mm of insulation under the floor.  A typical overlay system where the pipes may be laid in 25mm of insulation will result in big heat losses to the uninsulated part of the floor.

 

UFH is all about comfort, no hot / cold zones / no radiators taking up wall space etc.  It will not magically make a house cheaper to heat than the same house heated with radiators.

[JohnMo]

16 minutes ago, Rocket Ron said:

another thing I’d like to clarify about the suspended floors and the heat loss downwards. Are you sure that even an overlay system for underfloor heating would suffer heat loss downwards? This is contrary to what the manufacturers advice and I’m becoming confused so I came on here for independent advice

Simple science is

 

Heat moves to cold, the room is say 20 and the heating pipes 35. There is a 15 temperature difference. The only insulation will be the flour covering and any air gaps if you don't screed. Downwards the pipes are still 35, the ventilation gap will be atmospheric temp plus any warming gained from above, so say a cold design day close to zero. So now you have temperature difference of 35, resistance to heat flow is provided by about 25mm of insulation. You can easily calculate out the downward losses.

 

Now if you consider radiators the room is 20, your underfloor ventilation gap is still zero. Your radiator downward heat loss is 20, a reduction of more than 30%. If you added 25mm of insulation to the floor and had radiators your calculation would be the same but the heat losses 30+% lower.

 

Picking up the points made by @ProDave, low and slow is the way for UFH, but low temperature radiators will work in a similar manner, but take up wall space.

[Rocket Ron]

Thank you both so it could be more expensive to run underfloor heating than appropriately sized and installed radiators unless I add a mass of insulation to the subfloor is that what I am to understand?

 

if I installed underfloor heating, it would be to reduce the monthly expenditure on Gas and also for the comfort factor if it’s not going to save me anything in terms of running costs I may as well do as you suggest and stick with radiators

[JohnMo]

20 minutes ago, Rocket Ron said:

Thank you both so it could be more expensive to run underfloor heating than appropriately sized and installed radiators unless I add a mass of insulation to the subfloor is that what I am to understand

Yes

20 minutes ago, Rocket Ron said:

if I installed underfloor heating, it would be to reduce the monthly expenditure on Gas and also for the comfort factor if it’s not going to save me anything in terms of running costs I may as well do as you suggest and stick with radiators

No it may not reduce it, gas boiler efficiency may increase, but downwards heat losses may wipe those gains out, plus a little more.

 

I would find a local heat geek engineer or someone used to low temperature heating systems and get him to quote for installing or designing an efficient system, based on the boiler you have.

[marshian]

1 hour ago, Rocket Ron said:

Thank you for the valued input. The boiler has already been installed. It is a 35 kW condensing. Vailent I’m not sure of the model number right now.

 

another thing I’d like to clarify about the suspended floors and the heat loss downwards. Are you sure that even an overlay system for underfloor heating would suffer heat loss downwards? This is contrary to what the manufacturers advice and I’m becoming confused so I came on here for independent advice.

 

As @JohnMo said heat moves to cold - Insulation can slow down the movement 

 

I would not consider an overlay UFH system on a ventilated sub floor unless there was insulation under the sub floor and that's a very disruptive process if you are living in the house @Sparrowhawk and myself have both done it and the improvement is great in terms of energy saving but it requires careful thought and preparation - sub floors are vented for a reason

 

You really need to do a room by room heat loss - if you have this information you can size radiators to the room requirements and flow temps to maximise boiler efficiency - this video from Urban Plumbers will help to simplify the process of room by room heat loss

 

 

I'm running flow temps in low 30's - Return temps are mid to high 20's - Boiler efficiency is 97.5% when doing CH

 

To get to this position

 

I know exactly what my heat loss is in every room at -2.4 Dec OAT

I have no UFH it's all radiators in all 13 rooms.

The radiators are all sized to match the heat loss at low flow temps (Boiler is weather compensated and DHWP)

Every rad has the correct flow rate supplied by Danfoss RAS-B2 "pressure independent" TRV valves - I have all TRV's set to max (ie no intervention to manage room temps)

 

If you don't know your room by room heat loss you can't size your rads correctly for each room

 

If you've oversized rads you'll get overheating and need TRV's to manage room temps - this will shrink your CH circuit and result in more cycles so more energy used

 

If you've undersized some rads you need to up the flow temp to get those rooms to temperature - this will result in rooms where rads are correctly sized overheating so you'll use TRV's to control the overheat and it's the same result as over sizing rads

 

It's all just maths at the end of the day and it's not even difficult maths

[Rocket Ron]

Thanks again my boiler engineer has done the heat loss analysis and these are the requirements for Btu

[JohnMo]

I would work through 1 room in detail and check his calculations. A lot of plumbers will stick a finger in the air and use a rule of thumb, you definitely do not want that.

 

Not sure what units he is using but seems to be BTUs, if so I suspect a rule of thumb is used..

 

 

[Rocket Ron]

32 minutes ago, JohnMo said:

I would work through 1 room in detail and check his calculations. A lot of plumbers will stick a finger in the air and use a rule of thumb, you definitely do not want that.

 

Not sure what units he is using but seems to be BTUs, if so I suspect a rule of thumb is used..

 

 

Still expense, I think you might be right he asked me to go and get the measurements of the rooms for him, but he didn’t ask for the window sizes or anything

[marshian]

4 hours ago, ProDave said:

UFH is all about comfort, no hot / cold zones / no radiators taking up wall space etc.  It will not magically make a house cheaper to heat than the same house heated with radiators.

 

^ WHS - your heat loss determines your cost to heat the house - how you put that heat into the house doesn't matter 

 

Std scheduling of central heating in the UK are normally 10% lower than 24/7 heating but if your boiler can modulate to a low level and you run lower flow temps the consistant temp profile can reduce that 10%

 

I could go back to scheduled heating and get a 10% reduction in my energy use but it would save me just £15 in gas over a year - that's not even a decent evening in the pub  

 

If you improve the heat losses of the building (Improved insulation or insulation under the floor then you can expect to reduce the cost of heating the house because you've reduced the "heat loss"