Underfloor heating for extension and existing house

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Is it true that there are two underfloor heating systems? How would I plan to install a new system for my single storey extension and then for my existing downstairs.
 
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Wet throughout. So if only have rads at the moment in the existing then want to convert existing downstairs into part rad and part underfloor, and the extension all underfloor heating with some rads as backup, is that possible?
 
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Its possible, but needs pipe work going back to the airing cupboard or wherever the system splits from the boiler.


For UFH to work properly, you need to give it its own control over the boiler. Having it as a slave to the rad circuit is a disaster waiting to happen.
 
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UFH takes hours/days to respond (unless you cook the floor). Rads take 20 - 30 minutes (usually).


If the UFH is a slave to the rad controls then you'll never get up to the right temperature, or you'll have to run the system such that there is no point having it and you might as well spend the money on fancy rads.


The biggest problem we have with UFH is with people installing it without an understanding of how to control it; and also when the homeowner expects the system to react almost instantly like their rads do and have scant regard for open windows and doors.

It is an expensive thing to screw up. But great if done correctly.
 
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UFH takes hours/days to respond (unless you cook the floor). Rads take 20 - 30 minutes (usually).


If the UFH is a slave to the rad controls then you'll never get up to the right temperature, or you'll have to run the system such that there is no point having it and you might as well spend the money on fancy rads.


The biggest problem we have with UFH is with people installing it without an understanding of how to control it; and also when the homeowner expects the system to react almost instantly like their rads do and have scant regard for open windows and doors.

It is an expensive thing to screw up. But great if done correctly.

As always Danny boy is right on the money. I wish I got a quid for every UFH system where there was either too many controls or more commonly not enough controls. UFH takes a lot of designing & lots of consideration of lifestyle etc.
 
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We are planning to have two rear extensions built. One will be 5m wide and 8m deep the other 5m wide and 4m deep. How would you recommend this is heated?

How is UFH best used for such space and how long should I allow for the area to heat up. Correct me if I am wrong but it is supposed to be left on most of the time at low temperatures right? A few hours to heat up just the floor?
 
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The floor is a big heatsink that is warmed up with water crculating round it between 4 and 50 degrees.

Rads work in the 70's.

You should zone the areas off and use programmable room thermostats to manage the system.

tell them what you want, and the optimisation algorithms should do the leg work.

I have 70 square metres of UFH downstairs, and rads upstairs all controlled with Honeywell Evohome which allows room level control of the entire system and I haven'#t touched the settings for nearly two years - it just does what it needs to do. Not having the missus moaning about being cold was worth the cost alone.

You are not heating "just the floor". You are heating a room with air changes, heat loss using a low temperature emmitter that happens to be tens of times larger than the high temperature emmitters in you other rooms.


For me, I sized the rads in my rooms to work as close to the running temperature of the UFH manifold as possible so my boiler doesn't have to run out of condensing mode for heating.

During the recent cold snap, the boiler only ever went above 60 degrees first thing in the morning for that initial heat up. The rest of the day it trundled along at 40 or so degrees.

I had the advantage of installing the system from the ground up EXACTLY how I wanted it rather than some site basher who just throws in what he is given by the developer.


This is also why you should get a separate heating contractor in for this side of the work, rather than the inhouse guy the builder will use. That will save you a lot of headaches in the future, even if there is a little friction on the build.

Pre-recession years, I was spending a good few months a year with another builder just going round North London putting right all sorts of abortions slung in by in house contractors.

Very lucrative it was too.:cool:
 
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The floor construction is the first consideration, then the heat source, the extension orientation in relation to the Sun & lastly Glazing.
 
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We did a 2500 square foot system a year or two ago. Whole house was 6000 feet. Stuck in a 60kW boiler and when we fired that bad boy up it was steaming away like a train for hours whilst it heated up, what must of been the better part of 3750 cubic feet of concrete.
 
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I knew a controls engineer who insisted the boiler be at least 30% oversized on big ufh jobs. If not he just walked away.
Though most plumbers usually listened to him.
That way there was few complaints coming back to him about the property taking ages to heat.
 
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I would probably agree as a consumer. Don't want to be underpowered. Does that actually mean it would consume more gas in the overall scheme of things or incur better fuel efficiency because the boiler does not need to work hard?

Also correct me if I am wrong but higher capacity boilers only cost a few hundred more than ones lower powered right?
 
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Oversizing a boiler is what I call the "Spinal Tap" method of specification. And is wrong. 30% is not montrously oversized, and assuming we are talking in terms of heat loss of the building rather than combined heating & hot water, then I can see the logic as it gives headroom for simultaneous demand.


Modern boiler electronics will cause it to short cycle and fail to give stable temperatures to the system. It will also make the boiler run less efficiently.

Long and low is better all round IMHO.




Jesus. Does this mean I agree with Nobcorn? I feel dirty. :rolleyes: :mrgreen:
 
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No it means you are agreeing with the controls engineer.

How many handsome attacks you had today errol? :LOL:
 
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