- Thread starter robgil
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Penners
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I have absolutely no idea at all, except to mention that presumably the values are going to be extremely variable, depending on thickness, dampness, and so on.
And in the absence of any better infotmastion, my amateur approach to the problem would be to err on the side of overspecifying the rad. You can always balance its output downwards, but you can never exceed its maximum.
And in the absence of any better infotmastion, my amateur approach to the problem would be to err on the side of overspecifying the rad. You can always balance its output downwards, but you can never exceed its maximum.
i did consider just putting in bigger rads but that would mean i would probably end up with an overpowered boiler. i dont think that would be a major problem apart from cost and as you say , it would be better to have too much, or at least too much capability than not enough.
the system i am trying to design though has to run rads upstairs and underfloor heating downstairs , so because u/f heating runs a lot cooler that conventional rads this means the rads have to be fed first so the cooler water then goes to the u/f heating systems.
if i dont get it as accurate as i can i may well end up with hot rads upstairs and cold floors downstairs.
the system i am trying to design though has to run rads upstairs and underfloor heating downstairs , so because u/f heating runs a lot cooler that conventional rads this means the rads have to be fed first so the cooler water then goes to the u/f heating systems.
if i dont get it as accurate as i can i may well end up with hot rads upstairs and cold floors downstairs.
chuckey
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If you use TPVs on the rads, which you should, they will close the rads down upstairs when their rooms have reached their set temperature. This will actually give you the totally opposite effect, because the hot water from the boiler will flow through the pipes upstairs and not loose any of its heat and then return to the UFH, too hot for actual use?
I was thinking of something like a thermostat sensing the temperature of the water going into the UHF circuit( 50 deg C?) and wiring it in series with the main thermostat. This way if the water going into the UFH is too high it switches off the boiler, if its low enough in temperature the boiler cycles on the room thermostat. Its still a problem what to do with the too-hot water, if the upstairs rads are satisfied and the downstairs is too cold.
Frank
I was thinking of something like a thermostat sensing the temperature of the water going into the UHF circuit( 50 deg C?) and wiring it in series with the main thermostat. This way if the water going into the UFH is too high it switches off the boiler, if its low enough in temperature the boiler cycles on the room thermostat. Its still a problem what to do with the too-hot water, if the upstairs rads are satisfied and the downstairs is too cold.
Frank
Aidan
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CIBSE guides, probably available at a good reference library, used to have thermal conductivities for almost everything; you use the conductivity, thickness and surfaces' emissivity (I think, long time since I used it) to calculate the U value in W m^-2 K^-1). It must be variable depending on how damp and/or rotten the thatch is.
Aidan
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Aidan said:
PS Just read the rest of your post (and Penner's, which I have echoed
). The rads-first-then-UFH idea won't work IMHO. The UFH has a much longer heat up time than the rads and will often be running when the rads aren't. In fact, the UFH is often run 24 hours. You need a mixing valve on the UFH system to give a reduced flow temperature. I'd suggest a modulating boiler with weather compensation and a 3-port mixing valve set (also with weather compensation) for the rads. The heat emission from UFH is quite limited if you keep below the maximum recommended floor temperature, so older, less-insulated, properties often can't rely on UFH alone to supply the design heat load.
If you are going to combine radiators and underfloor you are probably better off oversizing the radiators so they can use a lower water temperature too. There are radiators purpose designed to work at low temperatures for use primarily with heatpump systems, but rads with 2-4 times the normal heat output at delta 65C (?) will work effectively.
I agree with the other posters that you will need to separate the rads and underfloor circuits as simply putting them in line doesn't take the different heating characteristics into accoung (e.g. rads have fast action and underfloor has slow action).
I wouldn't attempt to design the heating system yourself, get an underfloor heating company to do the calcs. even if you end up DIYing the installation it will be worth the £350 or so to get an efficient design.
I agree with the other posters that you will need to separate the rads and underfloor circuits as simply putting them in line doesn't take the different heating characteristics into accoung (e.g. rads have fast action and underfloor has slow action).
I wouldn't attempt to design the heating system yourself, get an underfloor heating company to do the calcs. even if you end up DIYing the installation it will be worth the £350 or so to get an efficient design.
getting someone to design the system might be a good option , ive put in pleanty of heating systems in the past but all on new builds and none using underfloor heating.
one thing i am not quite getting is where in the system , if using a three port valve do i put the rad system? or do i use two separate systems t'ing off at the flow and return on the boiler side?
i am not so sure about over sized rads , the rooms are quite small and i would like to keep rad size to a minimum and aslo keep them as officiant as possible.
are there any other options to heat the upstairs (2 bedrooms and a landing) other than rads? i could go wet underfloor but the installation will require me to either lift the floor boards or strip the downstairs ceilings , the ceilings down stairs are a mixture of fiberboard (which i will want to replace sometime in the future) and lath and plaster (around 30% that i don't really want to take down at all). the floor boards on the other hand are a mixture of 70% new boards and 30% old wide boards so again i will be restricted to what boards i can lift , so with this in mind uf heating upstairs will be a last last resort if not a never ever.
the rooms upstairs should keep the heat in as the roof is thatched and although the ceilings will be vaulted the rooms are right up in the eves anyway with only around 2.5 feet of walls , the rest is roof so the thatch should provide a good roof insulation.
i have looked at perimeter wet heating in the skirting boards type installations but i have no skirting boards nor will i ever want to install any.
i have thought about electric but don't see the point if i have an oil fired combi and i have even thought about no heating up there at all but i dont think i want to take the chance at relying on the downstairs heating to heat the whole house.
one thing i am not quite getting is where in the system , if using a three port valve do i put the rad system? or do i use two separate systems t'ing off at the flow and return on the boiler side?
i am not so sure about over sized rads , the rooms are quite small and i would like to keep rad size to a minimum and aslo keep them as officiant as possible.
are there any other options to heat the upstairs (2 bedrooms and a landing) other than rads? i could go wet underfloor but the installation will require me to either lift the floor boards or strip the downstairs ceilings , the ceilings down stairs are a mixture of fiberboard (which i will want to replace sometime in the future) and lath and plaster (around 30% that i don't really want to take down at all). the floor boards on the other hand are a mixture of 70% new boards and 30% old wide boards so again i will be restricted to what boards i can lift , so with this in mind uf heating upstairs will be a last last resort if not a never ever.
the rooms upstairs should keep the heat in as the roof is thatched and although the ceilings will be vaulted the rooms are right up in the eves anyway with only around 2.5 feet of walls , the rest is roof so the thatch should provide a good roof insulation.
i have looked at perimeter wet heating in the skirting boards type installations but i have no skirting boards nor will i ever want to install any.
i have thought about electric but don't see the point if i have an oil fired combi and i have even thought about no heating up there at all but i dont think i want to take the chance at relying on the downstairs heating to heat the whole house.
My system has rads upstairs, underfloor downstairs and in some of the upstairs too.
The heat pump will feed a 2 port valve which tees off the radiators and the primary underfloor manifold, zone manifolds are the taken off that. That way the rads or the underfloor can call for heat independently from the pump or both together.
As heat pumps are more efficient at lower temperatures it would be wasteful to heat to 55-65C then blend down for the underfloor so I'm going to oversize the rads to suit a lower flow temp. I'm planning on using repro column rads to replace failing pressed steel and I don't think the small loss in room space is a problem, but my house isn't a little cottage. At the moment I can't afford the new rads so this winter we may discover how seriously under capacity the old ones are with a lower flow temp.
The heat pump will feed a 2 port valve which tees off the radiators and the primary underfloor manifold, zone manifolds are the taken off that. That way the rads or the underfloor can call for heat independently from the pump or both together.
As heat pumps are more efficient at lower temperatures it would be wasteful to heat to 55-65C then blend down for the underfloor so I'm going to oversize the rads to suit a lower flow temp. I'm planning on using repro column rads to replace failing pressed steel and I don't think the small loss in room space is a problem, but my house isn't a little cottage. At the moment I can't afford the new rads so this winter we may discover how seriously under capacity the old ones are with a lower flow temp.
Ushy M
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robgil said:
Our upstairs rooms look very like yours (from your 'stained beams' pics). It's true that in still air thatch is indeed a very good insulator, but the construction method does leave you potentially open to draughts, and this is what we really found made our house so freezing cold the first winter we were here (though we are on the top of a hill facing north!). I'd err on the side of caution with your rads to make sure you've got plenty of capacity, and find and fix any obvious draughts e.g. windows (metal ones can be draughty in my experience), and any holes/gaps between your beams/rafters and the plaster - we found lots of these. Did you decide about the woodburning stove by the way?