Floors dug up - should we put in underfloor heating??

[MeldrewsMate]

But all this doesn't answer the OP's question B from post no.1...

Yes, add edge insulation wherever you can.

@Madrab seems to be swimming against the tide here, so I need to speak up and support his argument.
UFH gives an equivalent level of comfort at lower air temperatures because the human head is more tolerant to cold than its feet. Warm air rising from the feet area satisfies this need, so the room can be colder with UFH than with rads, thus burning less gas. This only applies IMO if the user has a predictable heating habit. One argument of @winston1 's that I agree with is the waste of energy heating a house that isn't occupied. It's the argument of cost vs. convenience, and that's a decision of the present and subsequent users.

The OP appears to have gleened this nugget of info just after he needed it (the very definition of experience). Having already installed rads then he must dig deeper into his pockets to have fully functioning UFH now, or run the risk of only finding installation faults once he comes to commission installed UFH pipework in ten years; that's his call exclusively.

 

[fixitflav]

From your links, opinion seems to be divided on the question of leaving CH on continuously. I can’t see anything there about rads vs UFH, which this thread can’t agree on. Also, have they (the Energy Saving Trust) done any tests? One would like to think they have, but the article doesn’t mention it, and we can all have theories. It does refer to the point I made about constantly-on being better for the building structure.

It's a given that a certain amount of energy is constantly leaking out of your home (how much will depend on how good your insulation is). The Energy Saving Trust says if you're keeping the heating on all day you're losing energy all day, so it's better to heat your home only when you need it.

That's true, but there's other things to consider - lower roomstat setting, and benefit to the building structure.

 

[SpecialK]

You need the blue expansion edge insulation all the way around the slabs. This takes up the expansion when the slab is heated/cooled.
Add perimeter PIR insulation around external walls.

If you can work out where the manifold can go and run pipes to the boiler that would help. Also zone the heating between UFH and rads.

 

[muggles]

Indeed so it costs a lot more to run.

It actually costs a lot less to run

 

[Madrab]

@houseonahill ... apologies if your post was a little hijacked.

Yes, if UFH is appealing then get the pipework and insulation in. If you are proposing using a concrete slab and screed then get in as much insulation on the sides and underneath as you can afford. Don't forget the rest of the space - walls and windows/doors - You want as much heat to be released into the room and the least transferred through windows, walls and the ground.

IN MY EXPERIENCE - and with other clients that I have installed, under floor heating is currently working out to be more than 10% cheaper to run day to day. The system does need to be installed and used properly of course and it does need to be used differently than conventional radiator systems due to the way it heats the space, so will need a change in habits until it becomes the norm.

 

[Diver Fred]

Been involved with a couple of UFH installations. Both electric and both in bathrooms.
No 1. 800w/4Msq; heating on for 2 hours in morning, 1 hour in evening. Floor temp is set 22 degrees C. Room is comfortable for morning - wife is a cold soul... And is enough to keep the chill off in the evening. Running cost is about 1 unit a day. 1 inch of insulation internal, 4 inches of insulation external.
No 2. 200w/1Msq; heating on permanently. Floor Temp is set to 22 degrees C. Room is warm and dry. Walls are 24inches thick stone. with 1 inch insulation inside. Running cost is cost is about 2 units per day.

 

[winston1]

I think the whole argument comes down to where it is installed, how it is installed and how it is used. If it is installed as a complete package with good insulation and used properly it seems there are efficiencies to be made over traditional CH running costs. Whilst I cannot find anywhere case studies that state that UFH is more efficient, I also can't find any that says it isn't, in fact the information I seem to be able to find is that the jury is still out.

That being said, I retrofitted my downstairs to overlay UFH with wood, tile and carpet topping and have dropped my gas costs by over 10% in the last year. The house is much more comfortable, the whole space is much more evenly warmed, one room that had 2 radiators totaling 3Kw never seemed to get warm enough or there were cold spots/draughts, there's no longer an issue with that and the UFH rating for that room is now approx 1.7kw (22m2@76Wm2) So my experience is that it certainly is more efficient. That and the cooler system (boiler currently set @ 50deg) means less stress on my system, so there are efficiencies to be made in other areas too.

Added to that I now run my stats @ 19Deg which is 2 deg less than I did before - The energy savings trust states that dropping a room temp by 1deg can save up to 10% in energy costs - so in my experience it's a win win.

So you have dropped the room temperature by 2 deg so according to your last sentence you should be saving 19%. Yet your gas costs have only reduced by 10%. Something wrong there. Perhaps your UFH is not more efficient after all.

 

[winston1]

just remember underfloor does not have the same response time to heating the room as radiators do it needs to be on a lot longer

Indeed so it costs a lot more to run.

So how can it be cheaper if it needs to be on for longer?

 

[fixitflav]

So how can it be cheaper if it needs to be on for longer?

Being on for longer (on the programmer) doesn't mean it can't be using less gas. The boiler may modulate down or off during that time.

 

[Madrab]

.

 

[Madrab]

So you have dropped the room temperature by 2 deg so according to your last sentence you should be saving 19%. Yet your gas costs have only reduced by 10%. Something wrong there. Perhaps your UFH is not more efficient after all

It actually reads over 10% but that's just a rough average. The last sentence says up to 10% but as we all know these figures aren't ever absolutes. The fact that there is even a 1% saving compared to the previous setup, means that it is working more efficiently and that's with all the costs currently rising ... seems pretty self obvious to me.

 

[winston1]

The fact that there is even a 1% saving compared to the previous setup, means that it is working more efficiently and that's with all the costs currently rising ... seems pretty self obvious to me.

But you could get that just by turning the stat down 2˚ without changing the heating system. Efficiency by the way is the ratio of energy out over energy in. Nothing to do with costs.

 

[Madrab]

But you could get that just by turning the stat down 2˚ without changing the heating system

Yes but for the house to 'feel' warm enough for us with the old system, the stats needed to be set to at least 21Deg .. with the UFH the house feels just as warm, if not warmer, as it did before with the setting @ 19Deg. My other half and clients can't stop raving about the obvious difference it makes.
This isn't about turning the heating down by 2deg and then feeling cold, which is what would happen if the old system was set lower, what would be the point of that. I want my system to warm the house to what I feel comfortable with, as anyone with central heating wants I would suggest.

So if UFH does the same job, if not better, at heating the space with a system that runs cooler and whose stats are set 2 degrees lower and it saves money by physically using less gas into the bargain, then to me that is the definition of being more efficient.

 

[winston1]

Efficiency is energy out divided by energy in times 100%. What you think of as efficiency is something different, but however!

 

[Madrab]

Efficiency, as a mathematical formula is certainly what you describe ....

Efficiency as a definition can be - effective operation as measured by a comparison of previous and current production against cost

Unfortunately most people don't work with formula. Efficiency in 'real life' working terms for customers seems to be related to usage and cost. If they can get what or more than they had before using less energy than before and therefore cheaper, then that's considered as more efficient.

So to be clear IME UFH shows that in the cases I've seen it costs less in energy and therefore money to do the same or a better job than the old radiator system did before, personally I see that as being exactly the same thing.