Underfloor heating and Radiators

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Benny200

Registered User
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Folks,

I have UFH downstairs and rads upstairs. If I have both on at the same time will this use more oil - I would have thought no as the oil burner can only burn so mush and the pumps do the rest of the work?

Any thoughts?
 
Obviously, in very simple terms, your rads are going to remove heat from the water heated by the boiler and therefore cause it to fire for longer to maintain the water temperature set at the boiler.
 
Imagine you are only heating one room (i.e a small bathroom), the boiler wouldn't need to be on for very long to get the room to 20 degrees. You would use very little oil.

However if you are heating 2 floors, there is a large area competing for the oils heat, the boiler would need to on for a much longer time, burning a lot more oil.

The boiler produces heat at a constant rate. How long the boiler stays on for depends on the number of rooms competing for the boilers heat.
 
Thanks Davidoco,

I'm no use when it comes to these matters!

I'm finding the UFH expensive to run and I don't have the rads on for the same duration but if I have the UFH timed for a certain number of hours per day and I have the rads on for the same time, surely the burner can only burn for that duration and heat the water to the temp determined by the thermostat on the boiler and distribute it to both the floor and rads therefore using the same amount of oil but at least I get heaqt upstais also?

Benny
 
Not sure I understand what your saying, but for example if the boiler was timed to come on for 4 hours to heat 1 floor it would run for maybe 1 1/2 hours of the four and "rest" the other 2 hours, intermittedly of course, as there is less water to heat. If there were 2 floors to heat it would run for three hours and rest for 1. these times are for example only. the more water there is to heat, the longer the boiler cycle runs.
 
i don't know has anyone said it before but i think ufh dowstairs and rads upstairs is a waste of time.
 
Yes, it has been said before but I'm glad to see it popping up again.

We're just about to lay our concrete floors upstairs. We have UFH downstairs. Our plumber thinks it's waste to put UFH upstairs and has recommended rads. Reason: he said that we will only be upstairs for a short time in the morning so rads will provide 'instant' heat for the time we are up there. Having UFH upstairs would have upstairs warm whilst we are long gone downstairs and therefore is a 'waste'.

Opinions are very welcome!
 
I don't get much time to comment these days
but I could not resist stating the obvious

Yes your plumber is quite correct underfloor heating is less suitable for areas that are unnocupied for most of the time.
 
JoeHooker said:
i don't know has anyone said it before but i think ufh dowstairs and rads upstairs is a waste of time.
Click to expand...

Why do you say this?

I'm being advised not to have UFH upstarirs at the moment, and I'd like to see the counter argument.
 
Reason: he said that we will only be upstairs for a short time in the morning so rads will provide 'instant' heat for the time we are up there. Having UFH upstairs would have upstairs warm whilst we are long gone downstairs and therefore is a 'waste'.

That's the reason my plumber gave me!
 
Heat will rise from downstairs so if you had underfloor upstairs the stats would cut out even sooner . I have a bungalow & the comfort of the underfloor heating would make me very slow to go back to rads again.
 
Bear in mind to heat the Under floor pipe water you only need to heat the water to approx 30-40*C.
With Rads you need almost boiling water hence your boiler will run longer and burn more oil to get it to this temp.
 
That's actually one of the biggest questions I have: if you have a mix of UFH and rads, you'll need two temperatures. This can be done, obviously, but my understanding is that (gas) condensing boilers operate most efficiently at the (lower) temperature used by UFH. Is this correct? If it is, surely it's best to have UFH throughout? Sure bedrooms only need heating at very specific times, but can't zones with a separate timer and themostats take account of that?

This whole area seems a real can of worms, in terms of the amount of conflicting advice out there....
 
A boiler will condense once the return temperature is 20 deg c lower than flow temp, as for the output, is it better to run a heating system for short period of time at a high temp as for rads, or a lower temperature for long periods as for underfloor, for myself i think underfloor for areas that are used often is great, but for bedrooms, bathroom i prefer the quick response time of rads.
 
from what I've read on the internet, mixing high temperature and low temperature heaters is not a good idea.
I'm talking in the case of heat pumps there, but I suppose it would be the same problem with gas boiler (since it's more efficient with low temperature heaters), but I don't know about oil...
the reason is explained there much better than what I could say:
[broken link removed]
It sounds quite logical to me
the solution would then be, as ang1170 said, separate timers and thermostats upstairs. I think that is what we'll get for our future house...
 
ang1170 said:
That's actually one of the biggest questions I have: if you have a mix of UFH and rads, you'll need two temperatures. This can be done, obviously, but my understanding is that (gas) condensing boilers operate most efficiently at the (lower) temperature used by UFH. Is this correct? If it is, surely it's best to have UFH throughout? Sure bedrooms only need heating at very specific times, but can't zones with a separate timer and themostats take account of that?

This whole area seems a real can of worms, in terms of the amount of conflicting advice out there....
Click to expand...

As someone who has had UFH downstairs, and rads upstairs, since 1998 - 10 years now - I can assure you that the ufh/rads mix is a bad idea. You are correct about the requirement for both heating systems being different - and this is the cause of the problem - whatever you pick, imho, they should be complementary.

I built a new house last year, and put UFH in basement, ground floor, first floor and garage. I run it all off LPG and solar. IMHO, oil burners are fundamentally unsuited to UFH due to the nature of the oil burners not being able to modulate flame temp. Gas can.

If you still want to use rads upstairs, use a high performance rad like those from Solo - see them at http://www.energyrl.ie they only use 26 degree water (same nearly as UFH), and contain only 300cc of water, so they would work better than ordinary rads.

I still like my UFH everywhere, though..........and don't let someone talk you out of it if it's what YOU want - they're not living in it, you are.........
 
I have UFH upstairs. It only comes on for the evening heating cycle, so the room is nice and comfortable temperature wise when going to bed, during the night, and still in the morning when getting up ie. all the time that the room is occupied! I don't see much waste there, except maybe for those who prefer a bedroom to be cooler during the night.
As regards the rooms downstairs heating those upstairs - I would consider it very bad build quality if that was happening to any significant extent. There is insulation under the heating pipes upstairs to prevent heat being "lost" into the precast concrete floor underneath them. This insulation, along with the precast concrete beneath it, and the insulated slabs beneath that, pretty much prevent any heat coming up from downstairs.
I still have not got used to the feeling of getting out of bed on a cold winters morning and feeling the warmth of the floor underfoot :)
 
bobby04 said:
This insulation, along with the precast concrete beneath it, and the insulated slabs beneath that, pretty much prevent any heat coming up from downstairs.
Click to expand...

This construction would not be found in your typical house selfbuild or not. It's ideal of course well done.

Flooring
Screed with UFH Pipes
Rigid Insulation
Precast slab (hollowcore)
Rigid Insulation
Plasterboard.
 
davidoco said:
This construction would not be found in your typical house selfbuild or not.
Click to expand...

Prehaps, but what would be standard at the very least, is the insulation under the UFH pipes upstairs. That alone I would have thought would limit any benefit from heat downstairs?
 
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