The house was built in 1886 and so the suspended timber ground floors don’t have any insulation in them. They are designed to be a ventilated space so there is a health current of air flowing under the floors. This makes for quite a cool floor especially in winter with a cold breeze.
Of course there is heat loss through the floors but with thick underlay and carpets this can be reduced. Properties that have sanded floor boards have a much higher heat loss due to the temperature difference and also the number of air changes the room will experience.
To carry out any insulation to the floors is a tricky job; it either calls for the insulation to be fitted from the underside of the floor boards or the floor boards taken up and the insulation fitted from above. the space below this property’s flooring was about 400mm so only enough to crawl along on one’s back and not one where you can carry out hours of tricky work. Therefore the floor boards were removed and cut up into fire wood for the log burner.
To allow the 16mm heating pipe to pass over the joists a 20 x 20mm groove was routered into the joists at 150mm centres. At this spacing the floor would need 143m of pipe.
There are many ways of insulating the floors and we found the simplest and cheapest to use 75mm of Rockwool supported by 3/4” laths and then 25mm of Kingspan on top to allow the heat to be reflected by the silver paper on the Kingspan.
This is a tricky process but quite easy and less irritating that using a glass wool product such has super glass insulation which has poorer insulation values and less robust in situ.
With all of the insulation in place it was time to start laying the pipe. The pipe must be unspooled from the reel by unwinding it so a small turntable was made to allow the pipe to rotate as it was unwound.
The pipe was held in place with either a piece of 9.5mm ply or a nail-in pipe clip.
Once all of the pipe was laid (yes there was enough!) we completed the reflooring of the floor deck with 18mm P5 chip board. This together with the 9.5mm ply made it back to the original finished floor height of 28mm above the joists as the floor boards were 28mm.
Prior to sealing up the pipework the connections were made to the existing heating flow and return pipework and these were tested for flow and delta T.
The flow and return pipework was sadly only 15mm with two other radiators feeding off the pipes. It was decided to T into the two 15mm copper flow and return pipes to see if there was enough flow to supply the floor. A temperature gauge was attached to the flow and return UFH pipe connections to see what delta T was available and so calculate the possible flow rate of the system.
With the (Viessmann 200w system) boiler and (Viessmann 150a) heat pump both working on a weather compensation heating curve and with an
Outside temperature of about 10°c at the time of testing the flow temperature was about 35°c.
This was shown on the temperature gauge as 33.3°c as a flow temperature and a return temperature of 24.4°c giving a delta T of 8.9°c which is exactly as we would have wanted it. With the other two radiators opened up fully the delta T increased to 10.3° demonstrating the slower flow rate as the other rads opened up.
There is no need for a mixing valve or additional pump on this installation as the boiler pump and heat pump, pump were quite capable of supplying the flow. There is no need to blend down the temperatures because the boiler / heat pump is working on weather comp and so automatically reduces the flow temperature as the outside temperature increases.
So does it work?
To test its effectiveness we measured the flow temperature and the surface temperature of the chip board with 2 temperature data loggers and plotted the temperatures over a 24hr period, see below.
The plot shows the floor temp reaching 22.5°c after about 5 hours of constant heating at a flow temperature of about 35°c
Boiler Bee Limited 