Underfloor heating and boiler constantly running

I moved into a house that has downstairs wet UFH and is split into 4 zones. My wife frequently works from home and ideally, it would be cheaper to heat the room she's working from. I've tested this and just set the room stat in the living room to call for heat. I've noticed that when the single zone is calling for heat from the boiler, the boiler is constantly running for hours. Is this normal? I appreciate that if the room hasn't reached the desired temp, it will keep running and due to the nature of UFH, this can takes many hours.

If the above is normal, it doesn't seem very cost-effective. I'm sure I read that the UFH will take hot water from the boiler and mixes it with cold to feed the system, so this in itself doesn't seem great and then to keep the bolier running all day? Does it call for heat from the boiler at a lesser rate using less gas?

Bearing in mind my comments about trying to save money heating one zone, if the boiler is running for hours anyway, would I just be better off heating all zones?

Assuming everything is working correctly (no faulty motorised valve or thermostat) how your using ufh may be problem.
You don't run it like a radiator system Sort out desired target temperature then use a back set temperature of no more than 4 C below that.
If you have a modern boiler it will modulate down to heat requirement.

Problem is, you can't just blast a block of concrete up to 70 degrees and a boiler doesn't easily dial down to producing water at about 30 degrees (or less if your house is well insulated) so you do need the mixer. All in, the cold water should come from the UFH return system so the heat the boiler is producing is going into the floor, you just need to appreciate that heating several tons of concrete will take longer than a few kilos of mild steel. Rather than just looking at the boiler and seeing it's active, you should measure the flow and return temps to see just how hard it's working..

Ultimately, due to the long response time of a screed based UFH you do end up just keeping them at temperature constantly, which might mean making the long hike to get it up to temp and then leaving it to cycle on and off. If you didn't fit the UFH yourself and know the spec of the insulation under the slab you may also be contending with it being woefully undersized; I'm not sure I'd put less than 200mm of kingspan under a wet UFH system but if there's a chance yours could be lacking then you may be pouring a lot of heat into the ground

Examine where the heat from your one zone might go; if you have uninsulated ceilings, solid walls all round, single pane glazing and a wife who feels the cold etc then your UFH might never be satisfactory without getting the floor to a temp that destroys the floor covering..

dazzler9000 said:

ideally, it would be cheaper to heat the room she's working from

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Only true if that room is insulated from the rest of the building to the same standards as a whole house is insulated from the external environment.
Approximately 100% of homes are not built like that.

Thanks for the comments so far. So, perhaps I am using it wrong.

I'd typically set it to switch on about 04:30 in the morning, so it's warm when we get up and then switch off about 07:30 if we're both off out to work, so I'd set the away temp to be very low. Then set it to come on at about 16:00, so it's warming up for when we return. At about 22:00, I'd set it very low again so it doesn't heat throughout the night.

Are you saying I should set it to about 4 degrees under my desired temp during the away time, so it doesn't drop too far?

As for insulation, I'm not convinced there is any. It's very hard to say what's under there. All I know is I had to lift some floorboards under the stairs once (no UFH there), and there were just floorboards and a void/crawl space under the house. I thought it wasn't great, but it wasn't until I spoke to a friend who was having an extension and UFH fitting and he told me about the masses of insulation boards going in .

The house is detached, open plan and has quite a few windows and doors. We also have two solid walls, which I'm hoping to get external wall insulation fitted in the next couple of years. So, definitely not the warmest house on the street.

Fortunately, we do have a log burner which does help out downstairs.

I've attached an image of my downstairs flooring, tiled kitchen and hallway, and engineered wood flooring. As you can see, it's very difficult to tell what's underneath. I've spent a fair amount of time wondering how I could insulate under the floor, but it's kind of difficult now.

I suppose I should get someone in to service it as well at some point. Maybe a job fo the summer. I'm in Southampton if anyone is local.

If you've got wet UFH and engineered wood or tile, plus you know that the house has a suspended timber floor then the long response time could be because the UFH has been fitted into grooved cement boards on top of the original floorboards (or on top of some skinny insulated boards on top of the original floorboards..) and then engineered wood on top. Absent any insulation under the UFH pipes, more than half the heat will disappear into the void beneath them.. The more insulation the better, but low amounts (10 to 40mm as one typically sees with under-tile boards) aren't going to work well

If you can fit into the void, you can insulate it, though it might not be the most pleasant job.. I've always wondered whether, if I had that floor construction, I'd take the easy route of using a blower to completely fill the under-house void with EPS beads..

I've got UFH & rads, for the UFH, I just set a temperature, say 19° (with a fallback of 14º from 9pm-5am) then let the thermostat decide when to call for heat.

A few weeks ago, the UFH would fire up once a day, in the morning, now the weather is a bit colder it's doing twice a day, mine is heating up screed though, not overlay boards.

I'm wondering if it would be more efficient now, to run the heating 24/7 at 19° and let the thermostat decide when to call for heat, not all the times the system is running will gas be being used, sometimes just pumping water around.

I would have expected your overlay boards to be insulated? if they aren't, then heat will be leaching away and you'll need to address this at some point. If you can get under the suspended floor, fitting PIR tight to the underside of the floorboards should help, or rock wool.

robinbanks said:

If you've got wet UFH and engineered wood or tile, plus you know that the house has a suspended timber floor then the long response time could be because the UFH has been fitted into grooved cement boards on top of the original floorboards (or on top of some skinny insulated boards on top of the original floorboards..) and then engineered wood on top. Absent any insulation under the UFH pipes, more than half the heat will disappear into the void beneath them.. The more insulation the better, but low amounts (10 to 40mm as one typically sees with under-tile boards) aren't going to work well

If you can fit into the void, you can insulate it, though it might not be the most pleasant job.. I've always wondered whether, if I had that floor construction, I'd take the easy route of using a blower to completely fill the under-house void with EPS beads..

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I thought those cement boards might be in use, but I can't prove anything until I get some access. This might be some time as I don't fancy wrecking the wooden floor. I may have another nose under the stairs when I get the time and see if I can figure out what's going on under the floor.
I'm quite tempted to just rip it all up one day and replace the wood and tiled floor as they aren't the nicest tiles and it's stressing me out to think of all that heat/money I'm potentially leaking into the ground. If I did remove the current floor coverings and exposed the joists, would it be a case of just pushing Celotex in between the joist? Is this sufficient?

Gaining access to the crawl space could be difficult and it wouldn't be a nice job. I suspect there are many rodents down there.

I did think filling up the void with some form of insulation would be the easiest route but I just assumed that void was there for a reason. I will do some research on this subject.

Mr Chibs said:

I've got UFH & rads, for the UFH, I just set a temperature, say 19° (with a fallback of 14º from 9pm-5am) then let the thermostat decide when to call for heat.

A few weeks ago, the UFH would fire up once a day, in the morning, now the weather is a bit colder it's doing twice a day, mine is heating up screed though, not overlay boards.

I'm wondering if it would be more efficient now, to run the heating 24/7 at 19° and let the thermostat decide when to call for heat, not all the times the system is running will gas be being used, sometimes just pumping water around.

I would have expected your overlay boards to be insulated? if they aren't, then heat will be leaching away and you'll need to address this at some point. If you can get under the suspended floor, fitting PIR tight to the underside of the floorboards should help, or rock wool.

Click to expand...

If I had my away temp at 14º, I think my boiler would be running most of the time. I can't justify the costs at the moment.

I don't know much about the overlay boards, I didn't realise they are or can insulated.

dazzler9000 said:

I suspect there are many rodents down there.

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Yeah but by the same token you might easily go to a pub and there be a load of Man Utd supporters there

dazzler9000 said:

just assumed that void was there for a reason

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In the olden days a suspended floor with vented void prevented ground based moisture affecting the wood, but if the space was chock full of insulation I've always considered it would have the same power to do so (after all, the cavity in the walls, blown full of waterproof beads does the same)

If you're getting down there to line out with insulation I'd go between and underneath the floor joists; going between with wool would be easier than with board, but going under with board would give a useful extra insulation to the joists themselves and support the wool

If the void isn't large enough to crawl round in you might be looking at taking up sections of floorboards instead, potentially a lot more work

dazzler9000 said:

I don't know much about the overlay boards, I didn't realise they are or can insulated.

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I was in Lidl the other day and saw a sort of shoulder shawl and back belt thing that was an electric blanket built in too. Got me wondering if the cheapest way to keep warm being sat in a cool room for long periods of time would be to have a low power electric heat source and a well insulated human. Friend of mine has an office chair made out of a Volvo car seat ("most comfortable seat I ever sat in and only 60 quid from a scrappie") with the heated seat part wired up to a 12v power supply.. I've just reminded myself that motorcyclists can get heated suits too..

Personally, I keep the rowing machine in the office and whenever I'm feeling a bit cold I do 5 minutes on it

robinbanks said:

If you've got wet UFH and engineered wood or tile, plus you know that the house has a suspended timber floor then the long response time could be because the UFH has been fitted into grooved cement boards on top of the original floorboards (or on top of some skinny insulated boards on top of the original floorboards..) and then engineered wood on top. Absent any insulation under the UFH pipes, more than half the heat will disappear into the void beneath them.. The more insulation the better, but low amounts (10 to 40mm as one typically sees with under-tile boards) aren't going to work well

If you can fit into the void, you can insulate it, though it might not be the most pleasant job.. I've always wondered whether, if I had that floor construction, I'd take the easy route of using a blower to completely fill the under-house void with EPS beads..

Click to expand...

Still looking into insulating my suspended floor. Just found this - Q-Bot looks great and might be easier with limited access.

I'll start another thread to see if anyone has used them.