towel radiator thermostatic valve

[athlonoc]

My home and water is heated via a mitsibushi ASHP. Its less than a year old and wanted some advice for the forthcoming winter as we struggled to get the balance right when we moved into our home in January this year.

 

The house also has UF heating downstairs and rads upstairs.

 

It seems the general flow of heat from downstairs keeps upstairs warmish and we found running the stats downstairs at 21 stopped the need for the upstairs rads to come on. However the on suite which is tucked away is off our main bedroom and  away from the main flow of heat in our house and has a towel radiator with no thermostatic valve on it. For us to make this room heat up we would need to turn off the radiators upstairs and put the single portable stat in the on suite to make it heat up and ramp that up to say 22 or 23 degrees. 

So I wondered what anyone's thoughts were putting an electric thermostatic valve on this towel radiator. I can't help but think an electric 300w or 400w TRV could be cheaper to heat up than a single towel radiator using the CH system to pump hot water to just that rad. As I've come to learn ASHP heating systems take an eternity to generate heat but once done in a well insulated home it seems very good.

 

Does this impact the heat of the water in the rest of the CH pipework upstairs? What stops the heated water in the towel radiator seeping into the rest of the water in the system?

[ProDave]

There is a little confusion here.

 

It's not ASHP's that take an age, but under floor heating.  Even heated by a gas or oil boiler, UFH takes a long tome to warm up.

 

I think you are talking about an electric heating element for the towel rail?  Not a "300 or 400W TRV"?

 

They work well, but be aware if you do turn the upstairs radiator circuit on, all the heat in the towel rail from the electric heater will be distributed to all the radiators.

[JohnMo]

You could also dual fuel the towel rad, add an electric element to the existing towel rad. When you rads are on the heat is supplied by ASHP, or when off by electric element.

[AliG]

40 minutes ago, JohnMo said:

You could also dual fuel the towel rad, add an electric element to the existing towel rad. When you rads are on the heat is supplied by ASHP, or when off by electric element.

 

Yes. but not at the same time. You need to shut off the valve when the electric element is on. Normally this would be done to run just the towel rail in the summer.

 

It looks like you have a downstairs thermostat controlling the UFH and an upstairs one controlling the radiators.

 

So to get just the en suite radiator on you turn up the upstairs thermostat and turn the TRVs down/off on the radiators. It will be cheaper to heat this one radiator from the ASHP than from a direct heating element. The ASHP has the CoP effect so if you put 100W in you will be getting 300W out. You won't get that benefit on a heating element although it could be offset by losses in the pipework and these could be quite large running the whole system for one radiator, but if it is winter they will still be helping to keep the house warm, so they aren't really lost.

 

A 300W heating element will probably not put out as much heat as running 50C hot water through the radiator from the ASHP. A pretty small towel rail puts out around 2000-2500BTUs with 70C water in it. 2000BTUs is almost 600W. At 50C, it probably puts out the equivalent of around 400W. Again though you would get this heat cheaper from the ASHP than a heating element.

 

I think what you have been doing is the best way to run it.  It might be more efficient if you connected everything to the downstairs thermostat so the en suite radiator only ran when the UFH was on (assuming the other TRVs are switched off), but this runs the risk of overheating the en suite if it has no thermostat or TRV.

 

 

[JohnMo]

1 hour ago, AliG said:

en suite radiator only ran when the UFH was on (assuming the other TRVs are switched off), but this runs the risk of overheating the en suite if it has no thermostat or TRV.

Assuming the heat pump is weather compensated, you could just balance that radiator, to prevent over/under heating. If it gets too hot close in the lockshield valve a little until heat in matches room loss.

[athlonoc]

Hi all and thanks

 

I hear what pro Dave says and yes I understand - my misunderstandings and thought that too, that heat in that towel radiator would get lost once the system pushes ASHP heated water about(upstairs only)

 

JohnMo, thanks - Is there any specific make and model to consider for a 500 x 1600 towel radiator?

 

AliG - Thanks, yes I have 5 stats for 5 rooms with UFH, all downstairs. I have no issue with these and all set to 21 as that's our desired comfort of heat all doors open and we don't touch it. - Perfect I guess.

 

The upstairs as stated is just the one stat. Its battery operated and I took it off the wall and mounted onto a cradle so I could move it about as it was originally at the top of the stairs. This was where most of the downstairs heat came from and caused that upstairs stat to believe the whole upstairs was at that temp which isn't correct. So putting it onto a cradle meant the main two rooms we use upstairs ( Bedroom and onsuite ) we had more temperature control. It lives either in our bedroom or our on-suite.

However neither of us like overly warm bedroom hence why were quite happy with the residual heat from the downstairs to fill the upstairs bedroom. It's almost perfect but what it doesn't do well is give us a warm on-suite first thing in the morning or when having a shower.

 

If we put the portable stat just in the on-suite and set that to say 23 or 24 degrees, it will get there eventually but it will mean turning all the other upstairs radiator stats to off, otherwise the whole house overheats. There will be occasions when coldness of winter truly sets in that we might want the upstairs radiators to come on for a while. I can't fault the idea of modern full electric Air Source Heating for water and house but it doesn't have that instant push of heat from Gas or Oil. So I thought I could put an electric element into the towel radiator to give the towel radiator some heat on a timer, it wouldn't impact the rest of the house but I guess that it's not the most efficient way to heat water. 

[JohnMo]

4 minutes ago, athlonoc said:

Is there any specific make and model to consider for a 500 x 1600 towel radiator?

I just converted a normal towel rad to electric only using a Termo One thermostatic heating element.  The package comes with an adaptor to dual fuel (water and electric), so you can install the element and tie in the water pipe.

[AliG]

1 hour ago, athlonoc said:

If we put the portable stat just in the on-suite and set that to say 23 or 24 degrees, it will get there eventually but it will mean turning all the other upstairs radiator stats to off, otherwise the whole house overheats

If the upstairs radiators have TRVs these should modulate the temperature to some extent. If you set them to around 2 then the heating in the different rooms will only come on once it is cooler. You might have to play around to get the right setting. If you want to set it more accurately you can get wireless TRVs that actually have a set temp on them.

 

You shouldn't have to set the stat as high as 23-24 in the en suite. As I always tell my dad, the heating doesn't;t warm up faster when you turn it up, it just stays on longer. If you set it to 22 then it should modulate fine  once up to temperature whilst not getting as warm elsewhere. Again it may need a bit of playing around with. I have thermostats set between 20.5 and 22 depending on the room.

[ReedRichards]

I have all radiators and the bathrooms have towel rails.  A problem I find is with Weather Compensation; unless it's quite cold out the towel rails only get tepid so the towels don't dry out very quickly.  I would have thought that running UFH and a towel rail would make that even worse because the UFH would need an even lower output temperature from the ASHP.  Who wants tepid towels instead of nice warm ones?

[athlonoc]

10 hours ago, ReedRichards said:

I have all radiators and the bathrooms have towel rails.  A problem I find is with Weather Compensation; unless it's quite cold out the towel rails only get tepid so the towels don't dry out very quickly.  I would have thought that running UFH and a towel rail would make that even worse because the UFH would need an even lower output temperature from the ASHP.  Who wants tepid towels instead of nice warm ones?

Indeed I agree, but in my case the UFH is on one feed and the upstairs ( radiators) are on a separate feed.

 

I guess as with much of this stuff, it depends on the individual, the type and size of house, how you perceive the cold/warm and type of system you have running.

 

All in all I think I wanted to try and understand was whether getting a separate electronic thermostat attached to towel rail was a good way forward to heat just that one small on-suite room despite the installers telling me to leave it all alone as it will mess around with the COP/SCOP readings. They also advised against setting a timer for my hot water. ( another story ) 

[ReedRichards]

12 hours ago, athlonoc said:

Indeed I agree, but in my case the UFH is on one feed and the upstairs ( radiators) are on a separate feed.

 

But both feeds are from the one heat pump so having one zone for the UFH and a second zone for the radiators doesn't really help.   Maybe at the moment perhaps your ASHP is set to produce water at 30 C to meet the requirement of your UFH whilst it's mild out, but that means your radiators are fed tepid water at 30 C.  Or if you turned off Weather Compensation you could ask your heat pump to produce water at 50 C.  That would keep your towel rails nice and warm and the manifold on your UFH would use the return water to dilute the input down to the 30 C it needs but now you are running your heat pump much less efficiently.    

[athlonoc]

4 hours ago, ReedRichards said:

 

But both feeds are from the one heat pump so having one zone for the UFH and a second zone for the radiators doesn't really help.   Maybe at the moment perhaps your ASHP is set to produce water at 30 C to meet the requirement of your UFH whilst it's mild out, but that means your radiators are fed tepid water at 30 C.  Or if you turned off Weather Compensation you could ask your heat pump to produce water at 50 C.  That would keep your towel rails nice and warm and the manifold on your UFH would use the return water to dilute the input down to the 30 C it needs but now you are running your heat pump much less efficiently.    

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