Underfloor heating and radiators

[tekanaka]

House is divided into two zones, upstairs and downstairs. The downstairs has underfloor heating and 3 radiators. It used to be all run off of a very old cylinder boiler. In the summer I had that replaced by a Vaillant Ecotec Plus 837.

All through the winter partly because of our laziness the boiler has been running almost 24/7. Ie. we didn't program on/off times on the boiler. I've just now set up the programmer to follow some pattern of when we are in the house and when we are away, as it was with the older boiler.

However, what I've now noticed with the regular on/off cycles is that downstairs the underfloor heating takes forever to kick in, 3-4 hours before I feel the warmth. The radiators are searing hot straight away. This is somewhat the reverse of how it was before, the underfloor heating would be felt really quickly.

Is that possible that within a zone there could be some prioritisation to the distribution of heat? What else could slow down the underfloor heating kicking in? Would like to get my head around this before I go get professionals coming in and get 3 different opinions from 3 different chaps.

Thanks!

 

[seasickstevie]

Your UFH needs to be on a zone, time-controlled separately to the rads, so they're coming on a lot sooner.

 

[tekanaka]

Your UFH needs to be on a zone, time-controlled separately to the rads, so they're coming on a lot sooner.

Ah thanks. Is that the usual practice? So if I have two zones, my rads (upstairs+downstairs) would be on one zone and the downstairs underfloor on the second zone?

What's the reason for not doing one zone with both underfloor + rads?

Thanks

 

[seasickstevie]

What's the reason for not doing one zone with both underfloor + rads?

Like I say, the UFH needs to come on a lot sooner to give the concrete slab/screed, or wooden floor and floor covering time to heat up.
Unlike a rad that's directly in contact with the air in the room, there's inevitably a 'barrier' between the coil of pipe in the floor and the air in the room.

 

[tekanaka]

Like I say, the UFH needs to come on a lot sooner to give the concrete slab/screed, or wooden floor and floor covering time to heat up.
Unlike a rad that's directly in contact with the air in the room, there's inevitably a 'barrier' between the coil of pipe in the floor and the air in the room.[/quote]

Aha, ok I follow now. Thanks for the clarification.

 

[stem]

Most people I know with UFH leave it on 24/7, because as SNM has said, it has a much lower surface temperature (albeit a larger surface) and a much bigger thermal mass to heat when compared with radiators, so is much slower to heat up and also to go cold. This is part of its attraction in that it provides a nice comfortable, constant, even temperature.

Having said that, from what you say, if with your old boiler it did warm up more quickly than now, there must be another factor at play.

Condensing boilers work more efficiently at lower temperatures, so it may be that when the system was commissioned it has been set to run at a lower temperature. Whoever installed it should be able to advise.

 

[tekanaka]

Condensing boilers work more efficiently at lower temperatures, so it may be that when the system was commissioned it has been set to run at a lower temperature. Whoever installed it should be able to advise.

Hm, interesting. Ok will look into that. The installer turned out to be a rather complete muppet. Still sorting out niggles 6mo on. So I'd rather not have him back! Need to go find someone else, but trying to get educated about the system as much as possible beforehand.

 

[stem]

For your information, the temperature of the UFH is normally controlled via a blending / mixing valve at the UFH manifold / pump rather than at the boiler thermostat.

 

[tekanaka]

For your information, the temperature of the UFH is normally controlled via a blending / mixing valve at the UFH manifold / pump rather than at the boiler thermostat.

Very useful, thanks!

 

[seasickstevie]

This guy explains pretty much ...

https://www.youtube.com/watch?v=oFoaePN0c8U

 

[tekanaka]

This guy explains pretty much ...

https://www.youtube.com/watch?v=oFoaePN0c8U[/QUOTE]

That is an awesome and simple explanation! Thanks for sharing that.

Yep, and found my mixing valve. And the flow rate indicators.

Interestingly, it seems that the indicators are showing very low flow rates, almost close to 0. I think I may have a bit of a ballache, these flow rates are specific to how the pipes are laid, right? Well the numpties didn't leave any diagrams how they laid the pipes.

 

[Dan Robinson]

Be careful what you listen to from that guy. He has a habit of talking utter bollax

 

[Agile]

The manifold will usually have adjusters on each loop. The flow rate does not need to be that high but is ( should be ) set up to give the correct differential on the flow and return of each loop.

Regardless, the UFH needs to be timed to be on about TWO hours before you need the room to be hot.

Assuming the rads have TRVs then they can assist in pre-warming the room by setting them a little lower than would be usual until the UFH is up to temperature.

It can be quite difficult changing zones around depending on how pipework is arranged, usually easier to add a zone.

I can never understand any installers who fit UFH and rads on the same zone as it is bound not to please anyone unless they keep heating on for 24/7.

Tony

 

[Tipper]

My UFH goes on at 5am so that the house is nice and warm for 7am onwards. When I get my head around the programmable thermostats in each room I will set them up to have nightime setback of only a couple of degrees.
(Oh and my wife complains if the floor isn't warm when she gets out of bed! )