Barryscotland Posted November 21, 2021 Share Posted November 21, 2021 160 m2 of underfloor heating and a 240l unvented cylinder in a new build. On the building warrant it says a gas 15kw heat only boiler. My plumber is telling me I need minimum 18kw and a plumber who I was blethering to while I was fixing his van reckoned 12kw would be more than adequate. Any thoughts or sure fire way of working it out, I don’t want to undersize or overkill Link to comment Share on other sites More sharing options...
Gus Potter Posted November 21, 2021 Share Posted November 21, 2021 Was wondering single storey or double storey house? Link to comment Share on other sites More sharing options...
Barryscotland Posted November 21, 2021 Author Share Posted November 21, 2021 56 minutes ago, Gus Potter said: Was wondering single storey or double storey house? Bungalow, does have attic trusses but if we do convert the attic it will be a long time away. Link to comment Share on other sites More sharing options...
Gus Potter Posted November 21, 2021 Share Posted November 21, 2021 That's a good start Barry. As an aside I have a 1955 -1960 ex council house that I have.. been experimenting with, some regrets a times, on the other hand some parts are working out well. It has a mixture now of underfloor heating and radiators. New gas condensing boiler but just popped my head outside to see a huge plume of steam.. so maybe not condensing that well but the gas bills seem to be going down. We are still living in a building site but still happy. You starting point here is to see how well you can insulate the existing bungalow. You could look at external wall insulation, I'm not a great fan of filling cavity masonry walls as often with ex council houses say you have .. yes timber wall plates bedded in load bearing masonry.. they are only 3/4 of an inch thick but they are there! So you have to be really careful not to do something that causes them to rot. Next look at insulating internally. The big thing is the floors. On paper when you say go the the Kingspan U value calculator increasing the floor insulation does not appear to have as much bang for your buck as say doing the roof. But have a look at the gaps under the skirtings and around the edges of the floor boards! You'll be amazed at how much warmer you can make the place by cutting out the drafts and adding a bit of insulation to the floors. Now taking this (above) into account you are splitting hairs regarding boiler sizing. What about asking the plumbers if they can provide a boiler that modulates / can be adjusted between the two values. Do the work and insulate / make air tight carefully. Then if you feel the boiler is coming on too often and then shutting down (cycling) get the gas engineer to adjust the burner controls? 1 Link to comment Share on other sites More sharing options...
Barryscotland Posted November 21, 2021 Author Share Posted November 21, 2021 19 minutes ago, Gus Potter said: Next look at insulating internally. The big thing is the floors. it’s a new build with insulated slab, walls n roof space and each room is in its own air tight ish envelope so I’m thinking most of the time the boiler is only going to be ticking over, the hot water is also heated from the solar panels when power isn’t needed elsewhere. 19 minutes ago, Gus Potter said: Link to comment Share on other sites More sharing options...
JohnMo Posted November 21, 2021 Share Posted November 21, 2021 (edited) We have just moved in to our new build, with solar, and it produces no real power at this time of the year, will be great in summer. Assume you have calculated your heat demand, it should be much lower than either boiler is capable of, so we are only really looking at recovery time for the cylinder. Bigger will give you better recovery time, but if outside the modulation range of boiler the central heating demand will cause the boiler to go into short cycling, so then you get into having a buffer. So look at the specs of the boilers on offer to make sure you can safely run the heating on the days like now (7 or 8 degs) not worst case design days. Or do what I did, indirect combination thermal store, combi boiler central heating connected to coil only, heating tank to 40 degs (boiler central heating temp set at 60 deg and has a return temp up to 55 deg, so always just condensing). Domestic Cold water goes through DHW coil on it way to combi via mixer valve (set at 55 deg) to give combi preheated water to improve DHW performance. UFH connected to thermal store via a 2 way valve operated by thermostat. In summer TS heated by immersion from excess PV. Boiler needs to be able to take preheated water (Atag do, plus others, lots do not). Water hotter than set point of DHW, passes through boiler without boiler starting up. Edited November 21, 2021 by JohnMo Changed modulating to condensing Link to comment Share on other sites More sharing options...
Gus Potter Posted November 21, 2021 Share Posted November 21, 2021 Ah.. then if it's a new build then it probably will be ticking over. A few personal thoughts.. Now one decision I made was to say to my self.. hey look Gus.. do your best to get the place well insulated. That cuts down the normal Monday to Friday running costs. But the whole point of putting in this work is to create a place we can enjoy not just during the week but at the weekends. It's also important for kids.. they need to be able to feel that a house gets warm and cold from time to time.. how are they going to cope when the go away with the school.. or move later to a flat where they have a more testing environment ? I'm Scottish based so we like to party.. we have a big piece of glazing we can open to the outside elements. We also have a front door that gets's opened and shut as folk come and go. We like to have a few fags when we party.. so the windows are open too! We cook and eat stinky food! Now a heating system that can't be cranked up is not for us.. I'm a designer and while I talk to Clients about energy performance the best designers dig deep and explore how their Clients want to actually live and if they want to be able to show off their new home... have a party / dinner and folk are warm. Once you start digging then folk are not so keen.. when you say.. hey every one will have to wear long johns by the way if the want a fag and open the windows.. or if you have cooked some thing stinky.. or have say Stinking Bishop cheese which I like.. but few do. Another point is that my Mum is 93 years old. She does not appreciate a fancy heating system if she can't come to visit and the place is not a good 24 -26 degrees. Barry have a look at how you really want to live and take it from there.. you can still do great stuff that will give you a cracking house. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 21, 2021 Share Posted November 21, 2021 I did a full heating install in a 300m2 build, with insulated raft, and it ran at 18.5oC with an outside air temp of -7 with a £35.77 3kW Willis heater. There were 2 installed, but one tripped out over the xmas away period and I discovered it upon my return to site. That was with 2x 200mm open vents through the roof to atmosphere ( where we were due to connect the MVHR unit later downstream ). As above, if the fabric & ventilation heat losses are managed you can heat with VERY little input, so the 15kW device will more than suffice. I would put the UVC on W-plan ( hot water priority ) so it can focus on heating OR hot water vs the 2 combined. You mention a "heat only" boiler, but I'd recommend a "system" boiler so you get the expansion, pump and pressure gauge etc all in one box. Heat only will require a lot of kit outside the boiler so is unnecessarily complicated IMO. Plenty around from £600 upwards, but the Worcester Bosch for a grand is a decent machine with a very low modulation. Intergas and Viessmann IIRC offering as low as 1 1/17th!! Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 21, 2021 Share Posted November 21, 2021 4 minutes ago, Gus Potter said: Another point is that my Mum is 93 years old. She does not appreciate a fancy heating system if she can't come to visit and the place is not a good 24 -26 degrees. With 2 Willis heaters working on the above project the house would see 24oC without trying, and 26oC when we'd not babysat it closely enough and a bit of cheeky solar gain had been absorbed. The issue with "cranking up the heat" is the choice of emitter, and the thermal time constant of the dwelling. Most see 1oC temp swings over 24hrs, so there is no summer / winter, and no 'timed' heating event as such. A party would have to be anticipated and the house temp setting increased at least 12hrs prior to, to have any effect on the overall house temp ( if a passive raft is the emitter not radiators for eg ). Then you'll need to 'set back' prior to the party ending, so the house can re-acclimatise afterwards ( and not overheat you when the crowd of 100W heating elements leave after scoffing all the free food and sumping your best vino ). This is very much dependant on the fabric of the build and it's energy performance statistics of course. Link to comment Share on other sites More sharing options...
Barryscotland Posted November 21, 2021 Author Share Posted November 21, 2021 10 minutes ago, Gus Potter said: It's also important for kids.. they need to be able to feel that a house gets warm and cold from time to time.. how are they going to cope when the go away with the school.. or move later to a flat where they have a more testing environment Lol We’ve spent a year and a half in a single glazed caravan with no central heating…. My two kids (now 9 n 3) know what cold is but surprisingly it’s not one of the things they complain about. We’re also Scotland, we went into our new build today which is nearing the end of first fix but still no front door fitted and our first thought was “ this is warmer than our caravan”. In hindsite should of spent the extra on a swanky warmer caravan. 10 minutes ago, Gus Potter said: Link to comment Share on other sites More sharing options...
Gus Potter Posted November 21, 2021 Share Posted November 21, 2021 6 minutes ago, Nickfromwales said: I did a full heating install in a 300m2 build, with insulated raft, and it ran at 18.5oC with an outside air temp of -7 with a £35.77 3kW Willis heater. There were 2 installed, but one tripped out over the xmas away period and I discovered it upon my return to site. That was with 2x 200mm open vents through the roof to atmosphere ( where we were due to connect the MVHR unit later downstream ). As above, if the fabric & ventilation heat losses are managed you can heat with VERY little input, so the 15kW device will more than suffice. I would put the UVC on W-plan ( hot water priority ) so it can focus on heating OR hot water vs the 2 combined. You mention a "heat only" boiler, but I'd recommend a "system" boiler so you get the expansion, pump and pressure gauge etc all in one box. Heat only will require a lot of kit outside the boiler so is unnecessarily complicated IMO. Plenty around from £600 upwards, but the Worcester Bosch for a grand is a decent machine with a very low modulation. Intergas and Viessmann IIRC offering as low as 1 1/17th!! Nick Thank you for you posts.. learn something new all the time. I posted this a while ago but I made a DIY temporary UF manifold.. it's working great although I had a pro plumber to do the boiler as I was out of my depth with the gas. I've not touched it since getting it working about a year ago.. few controls.. just shows you how simple a UF heating system can be.. and cheep to maintain. Less valves, electronics.. it's good cost effective engineering. If you are not bald with the above have a look below. xxx Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 21, 2021 Share Posted November 21, 2021 Yup. The only thing missing is flow gauges so you can set the flow rates, but you can do that with a bit of maths ( length of loops vs % that you open each gate valve ) so all good. Nice Reliance TMV on that rig, so that will be plenty reliable for sure. Link to comment Share on other sites More sharing options...
Barryscotland Posted November 21, 2021 Author Share Posted November 21, 2021 19 minutes ago, Nickfromwales said: You mention a "heat only" boiler, but I'd recommend a "system" boiler so you get the expansion, pump and pressure gauge etc all in one box. Heat only will require a lot of kit outside the boiler so is unnecessarily We’re going heat only for ease of repair in the future, expansion chamber went on our last one and it was boiler of the wall and stripped to change it. Very little seems to be accessible on modern boilers. We won’t be looking to heat the house to anything above 20 degrees max, we are all used to caravan temperatures now and even in our old house the thermostat never went above 20. the calculated demand is 18kw but that’s going to be if everything is being heated from nothing? Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 21, 2021 Share Posted November 21, 2021 1 minute ago, Barryscotland said: We’re going heat only for ease of repair in the future Fair comment. 1 minute ago, Barryscotland said: We won’t be looking to heat the house to anything above 20 degrees max, we are all used to caravan temperatures now and even in our old house the thermostat never went above 20 The system should be designed to cope with the dwellings requirements, not the designers personal preferences. Your choice. 2 minutes ago, Barryscotland said: the calculated demand is 18kw but that’s going to be if everything is being heated from nothing? You'll not miss the other 3kW tbh, but I would go with the 18kW boiler if you intend selling at all? There's little difference in price, but those few bucks buys a lot of insurance. Link to comment Share on other sites More sharing options...
Gus Potter Posted November 21, 2021 Share Posted November 21, 2021 23 minutes ago, Barryscotland said: We’re going heat only for ease of repair in the future, expansion chamber went on our last one and it was boiler of the wall and stripped to change it. Very little seems to be accessible on modern boilers. We won’t be looking to heat the house to anything above 20 degrees max, we are all used to caravan temperatures now and even in our old house the thermostat never went above 20. the calculated demand is 18kw but that’s going to be if everything is being heated from nothing? Barry.. I bet you that at some point 20 C is not going to cut the mustard! Anyway before you set your hat on 20 deg C check what you need to do to comply with the Building Standards. Cut yourself some slack and make sure you can heat the house up from time to time above what you may want on a day to day basis. Also remeber that is is no fun feeling unwell and you can't just heat the house up.. see man flu.. horrible. You are going to spend all this money.. have a fab kitchen.. other stuff no one else has.. why, when it gets really cold here in Scotland (-20 deg C yes happened in Lanarkshire not just up North) not have a bit of spare capacity to keep you all warm. That is the great thing about Scotland is that it can get really cold and that is when you can come back into your castle and think.. did we not do well! Link to comment Share on other sites More sharing options...
SteamyTea Posted November 22, 2021 Share Posted November 22, 2021 Can't you get an 18 kW one that modulates down low and still condenses? Link to comment Share on other sites More sharing options...
Barryscotland Posted November 23, 2021 Author Share Posted November 23, 2021 On 22/11/2021 at 18:00, SteamyTea said: Can't you get an 18 kW one that modulates down low and still condenses? Looking at a green star 4000 and the boiler range is 3kw to 18kw so thinking that should do the job Link to comment Share on other sites More sharing options...
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