Alu Radiators
- Thread starter seanoge
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A neighbour who had a heat pump installed told me how good it was, until winter came, then he had a log burner installed to keep the house warm. 
maybe larger radiators
the challenge is getting the heat transfer with low flow temperatures
have you got space for larger radiators?
were new radiators installed or were the old ones kept?
I fitted new rads myself and was surprised how they heated up faster and more even heat across them than the old ones. I just got stelrads from Wickes
I now have a system with weather compensation (on a gas boiler not heat pump) and the flow temps are usually below 40 degrees but have no issue with the time it takes to warm up rooms, but the systemhad pretty large radiators anyway
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1. There is no difference in heat output of aluminium versus steel radiators of the same designated heat output. The aluminium one is likely to feel warmer more quickly, but will then go cold more quickly.
2. It is likely that the water going into the radiators with the heat pump is cooler than it was previously. This will cause it to take longer to heat a given space as the rate of heat transfer from radiator surface to air depends on the difference in temperature between the two.
3. I would expect you will require larger radiators. The only way to know how much larger is to do a heat loss calculation for the room, using the "delta T" figure of ((flow temperature - return temperature) / 2). From this you can calculate the size of radiator (heat output) needed to heat the room.
4. This will likely come out higher than the existing radiator. How to achieve the required heat output will need consideration of whether a double or triple radiator can replace a single or double, whether a wider / taller radiator is needed and what pipework alterations will be needed.
2. It is likely that the water going into the radiators with the heat pump is cooler than it was previously. This will cause it to take longer to heat a given space as the rate of heat transfer from radiator surface to air depends on the difference in temperature between the two.
3. I would expect you will require larger radiators. The only way to know how much larger is to do a heat loss calculation for the room, using the "delta T" figure of ((flow temperature - return temperature) / 2). From this you can calculate the size of radiator (heat output) needed to heat the room.
4. This will likely come out higher than the existing radiator. How to achieve the required heat output will need consideration of whether a double or triple radiator can replace a single or double, whether a wider / taller radiator is needed and what pipework alterations will be needed.
Due to the lower flow and system temps from a heat pump then the rads need to be at least 25% larger than normal boiler fed rads to equalise the output for the same space's heat loss.
....and just to add - the benefit with alloy rads are -
1) they are much lighter than normal rads
2) they conduct heat much faster than mild steel so they heat up, emit that heat and cool down faster than steel.
As suggested though, the heat output is the heat output, regardless of the materials used.
1) they are much lighter than normal rads
2) they conduct heat much faster than mild steel so they heat up, emit that heat and cool down faster than steel.
As suggested though, the heat output is the heat output, regardless of the materials used.
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You're supposed to use a heat pump a bit differently to a combustion boiler. It needs to come on earlier and stay on longer.
Did you not look all this up before you went ahead ???
...they are more expensive, which gives owners a warm glow of pride.
In fact the usual recommendation is to leave a heat pump on continuously - with it just being controlled by an air temperature thermostat. That way, the time it takes to get a room to the required heat doesn't matter. You may find in the coldest weather it is running more or less 24 hrs per day as it struggles to maintain the the temperature of the house.
Heat pumps have IMHO, been over-hyped, and are not really suitable for heating water in a typical British radiator based heating system. In other countries they normally have ducted warm air to heat the house and that is more suited to be powered by a heat pump.
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