Fan assist coil unit

[Desktop987456]

I have one of the attached heating coil unit (fan assisted) installed in my lounge. The Lounge is about 650sq.ft so instead of radiator we installed one of these. It works quite well, the unit's is one of the last in circuit and its valves are fully open, there's no thermostat installed with this unit. To keep the lounge warm it has always been running with heating on.
I was observing my gas usage for central heating, I had this heating coil unit off and (with 7 radiators heating) the boiler cycles efficiently (short burn time {6minutes} and longer off time{10 minutes}) with minimal gas usage.
Does anybody has any experience of how do I balance this unit?
If I install a thermostat with this will it help bring the gas usage down, can you recommend a good thermostat to attach with this unit.
Thanks.

 

[ShaunCorbs]

Try lowering the kw setting on the boiler if it’s off more than it’s on your boiler is oversized

 

[Desktop987456]

Try lowering the kw setting on the boiler if it’s off more than it’s on your boiler is oversized

Thanks I agree but if I turn on fan coil unit the burner time increases drastically and gas usage. How do I fit in a thermostat with this unit?

 

[oz-plumber]

Sounds like the system is working as required.
That fan coil unit would be rated at @ 10 kW - wouldn't it?
Having different forms of heating around the home can be problematic.
Radiator systems can be balanced to suit.
When you have radiator systems and fan coil systems, combined off 1 thermostat, you end up with problems due to the different heat transfer from each type of heat emitter.

There will be a bi-metallic thermostat in the fan coil unit, which will turn the fan on when the water is over (say) 50 C.
I have replaced the 50C thermostat with a 40C thermostat and the customer says it works better than before - may be a solution

 

[snowhead]

Is the room with the fan coil unit in too hot compared to the other rooms?
If you balance the system to reduce the flow to the unit you'll get less heat out of it during the time the main thermostat is calling for heat from the boiler.

 

[Desktop987456]

Is the room with the fan coil unit in too hot compared to the other rooms?
If you balance the system to reduce the flow to the unit you'll get less heat out of it during the time the main thermostat is calling for heat from the boiler.

Yes, it gets too hot and I have reduced the flow quite a bit to control the heat but I have observed when I turn it on the boiler stays on longer and consuming more gas. With fan unit off; the boiler stays on for 7 mins and off for 16 mins, with fan unit on; it stays on for 10 mins and off for 10mins.

 

[Desktop987456]

Sounds like the system is working as required.
That fan coil unit would be rated at @ 10 kW - wouldn't it?
Having different forms of heating around the home can be problematic.
Radiator systems can be balanced to suit.
When you have radiator systems and fan coil systems, combined off 1 thermostat, you end up with problems due to the different heat transfer from each type of heat emitter.

There will be a bi-metallic thermostat in the fan coil unit, which will turn the fan on when the water is over (say) 50 C.
I have replaced the 50C thermostat with a 40C thermostat and the customer says it works better than before - may be a solution

I think it is about 5-7 kw (18000-24000btu).
I agree with your analysis on different heating units on one system.
The thermostat on fan coil unit doesn't work, it never switches off! I have manually installed an old dial type thermostat but I think it switches off the unit at 25Deg C?

 

[oz-plumber]

I'm talking about a thermostat on the heating flow pipe.

Fan coil units ( as far as I am aware) have a thermostat on the flow pipe to activate the fan coming on.

From memory, these are @ 50C incoming flow,

I have replaced the 50C thermostats with 40C thermostats to make the fan come on earlier to bring the heating on in the room with the fan coil - as a ad hoc balancing attempt.

For the few I have done this to, customers seem to feel the fancoil and room temperature operate better.

Fancoils also have filters to protect the coil from airbourne particles clooging the fan coil.

You may want to check the filters

 

[Desktop987456]

I'm talking about a thermostat on the heating flow pipe.

Ok. I don't have TRVs on flow pipe of the unit. I am choking back the flow manually but even then the burner stay lit a lot longer. I will try to get a TRV on flow pipe to see if that helps.

 

[oz-plumber]

Not a TRV.
Google - Bimetallic Thermostat.

The fan coil is always going to allow flow through the coil unless you have a zone vale installed to shut the water flow off to the fan coil.

The bimetallic thermostat is usually wired inline with the fan, so the fan doesn't operate when the water temperature is not hot enough.
The fan boosts the heaters performance.

 

[Desktop987456]

Not a TRV.
Google - Bimetallic Thermostat.

Thanks, this is exactly what I want. I will look it up.