Wet underfloor heating adding a rad.

[Skewett]

Hi there, just after some advice. I have an underfloor system installed and at the time of laying I had a spare loop put in with a view to adding a conservatory. I've now changed my mind and want instead to add in a single radiator. I can see the unbroken loop protruding into the conservatory through an external wall. It has its own zone and thermostat and I can heat this loop up.

Can I just cut into this plastic pipe and add a radiator?

 

[Uheat – Jake]

Hi there, just after some advice. I have an underfloor system installed and at the time of laying I had a spare loop put in with a view to adding a conservatory. I've now changed my mind and want instead to add in a single radiator. I can see the unbroken loop protruding into the conservatory through an external wall. It has its own zone and thermostat and I can heat this loop up.

Can I just cut into this plastic pipe and add a radiator?

You could do this, however just beaware that you won't get the normal flow tempature through the radiator as UFH runs at a lot lower flow temperature.

 

[Skewett]

Thanks for that Jake, I hadn't considered that as an issue. The conservatory is going to have the insulated 'warm roof' fitted but we would want to use it all year.

Is there no way of increasing the heat at the manifold end on just that one loop?

When you say it won't reach a high temp, would that mean the rad would only ever get warm?

The advice is for my son and he has two downstairs towel radiators in bathrooms which I believe are also connected to his underfloor system somehow. He's just told me they get very hot.

 

[SJB060685]

If the loop is fed by the mixer that currently governs the operating UFH then uprsizing the radiator to coincide with the mixed flow temp should work. Some careful maths might be needed though.

 

[Skewett]

If the loop is fed by the mixer that currently governs the operating UFH then uprsizing the radiator to coincide with the mixed flow temp should work. Some careful maths might be needed though.

Thanks this is all good info.

If I find that the two towel rads are fed from a source which is easy for me to link into, would the water temperature (which I assume would come from the boiler?) be too much for the plastic pipework in the original loop.

I'm thinking maybe I could just attach the same feed as the two existing rads into the loop and remove it from the UFH circuit altogether.

 

[SJB060685]

At a warmflow bluebird today not firing.I checked there was 240v going into the rdb control which there was
so immediately got a control from the van but no dice same issue.So im getting 240v on my meter but no lockout light .Nothing completely dead.I plugged a mains powered grinder into the socket to test and nothing.
anybody any ideas?

Thanks this is all good info.

If I find that the two towel rads are fed from a source which is easy for me to link into, would the water temperature (which I assume would come from the boiler?) be too much for the plastic pipework in the original loop.

I'm thinking maybe I could just attach the same feed as the two existing rads into the loop and remove it from the UFH circuit altogether.

The UFH heating loop is usually mixed to a flow temperature of about 45°c and a delta T across each loop of 7°c, this insures a nice steady and balanced floor temperature across the slab, as well as protecting any screeds, floorings and bare feet etc from abnormally high temperatures.
IF this additional loop is fed from the same mixer then the flow temperature will only ever be what the mixer is set to and ideally an overheat stat is incorporated to cut power to the pump should the mixer fail.
Usually radiators are designed with a rad to room delta T of 50°c and a delta T of 20°c between flow and return.
However you could size a single radiator based on a flow temperature of 45°c and a delta T between flow and return of 7°c, this would mean the return temperatures from UFH and the radiator are equal and the mixer won't pull as many litres per minute as it would with a rad on a delta T of 20°c between the flow and return. You would also want an indoor sensor in the conservatory as it will be susceptible to high solar gain but you said it had its own thermostat didn't you?

The other option is as you say tie it into the boiler flow and return and bypass the mixer. You can keep it on its own zone, thermostatically controlled and fed by a higher mean flow temperature, meaning the radiator can be sized smaller.

Having said all this its not uncommon for UFH to cause starvation to rads on a cold day and a cold slab, then you need to start thinking about hydronic separation, hence why I said about careful mathematics.

 

[Skewett]

The UFH heating loop is usually mixed to a flow temperature of about 45°c and a delta T across each loop of 7°c, this insures a nice steady and balanced floor temperature across the slab, as well as protecting any screeds, floorings and bare feet etc from abnormally high temperatures.
IF this additional loop is fed from the same mixer then the flow temperature will only ever be what the mixer is set to and ideally an overheat stat is incorporated to cut power to the pump should the mixer fail.
Usually radiators are designed with a rad to room delta T of 50°c and a delta T of 20°c between flow and return.
However you could size a single radiator based on a flow temperature of 45°c and a delta T between flow and return of 7°c, this would mean the return temperatures from UFH and the radiator are equal and the mixer won't pull as many litres per minute as it would with a rad on a delta T of 20°c between the flow and return. You would also want an indoor sensor in the conservatory as it will be susceptible to high solar gain but you said it had its own thermostat didn't you?

The other option is as you say tie it into the boiler flow and return and bypass the mixer. You can keep it on its own zone, thermostatically controlled and fed by a higher mean flow temperature, meaning the radiator can be sized smaller.

Having said all this its not uncommon for UFH to cause starvation to rads on a cold day and a cold slab, then you need to start thinking about hydronic separation, hence why I said about careful mathematics.

 

[Skewett]

Great info again there so thanks for that. If I can find a decent point in the cupboard where my mixer/pump is and can attach a direct feed to the rad then could I use the existing loop that goes solely to the conservatory. The main thing I don't know is whether the plastic loop pipework, which was laid in prep for underfloor heating, would cope with higher temps needed to heat up a rad?

 

[SJB060685]

Great info again there so thanks for that. If I can find a decent point in the cupboard where my mixer/pump is and can attach a direct feed to the rad then could I use the existing loop that goes solely to the conservatory. The main thing I don't know is whether the plastic loop pipework, which was laid in prep for underfloor heating, would cope with higher temps needed to heat up a rad?

So you have a flow and return teed off after current mixer with blank offs on it?
If so these pipes should be capable of withstanding higher flow temps, however you might want to check with manufacturers first.

 

[Ben-gee]

Ufh doesn’t starve rads with a cold slab, as that is not how you run ufh!
Leave it on, with maybe a small set back in temperature overnight, and it is fantastic!

 

[SJB060685]

Ufh doesn’t starve rads with a cold slab, as that is not how you run ufh!
Leave it on, with maybe a small set back in temperature overnight, and it is fantastic!

You are correct. UFH is designed to run constantly and supply a nice even room temperature without large overshoots in room temperature. However what when a customer does not operate the system like this, as is often the case? You suddenly find yourself with a cold slab absorbing all the heat and low return temperatures, then your mixer is pulling more flow from a boiler pump, which can only supply so many LPM and CAN starve the rads in this situation.

 

[SJB060685]

Here is a video I asked a friend to put together explaining the issues with UFH and radiator circuits.