Any issue with oversized radiators?

after_shock3000

I'm renovating a house and there's and old oil boiler, microbore piping and radiators that are being removed and a new gas boiler/controls/plumbing/rads fitted.
I've been given some brand new unused rads that were for a job that never happened but they're quite a bit larger than what I think are needed for my own house.

I know you can adjust the thermostatic valve at the rad to control the output but I'm wondering if having very oversized rads could cause any issues that I haven't thought of?
I estimated the needed heat output for each room with the calculator here.

The 2 biggest oversizes would be:
Estimated: 2100 BTU -- Rad that I have: 6240 BTU
Estimated: 4900 BTU -- Rad that I have: 9076 BTU

Any issues with that much of an oversize?

corkgsxr

Long as you fit thermostatic valves it can't see a problem.

Dardania

often times with new installations, oversized radiators are installed to make the most of condensing boilers. The idea being that in order to get the return temperature to the boiler to allow condensation occur (where the real efficiency gains can be seen) for a given heat input to the room, you need to oversize the rad...

In your case, it should be fine, but just recalcualte your BTU outputs bearing in mind reduced flow and return temperatures. The old school (pre condensing boilers) way to calc was 82C flow, 71C return (suspect your BTU numbers are based on something similar) whereas with condensing boilers they typically look at 70C flow, 50C return (which needs a bigger rad to get the same heat output...)

Wearb

Don't reduce your flow/return temperature too much, even condensing boilers have their minimum.

Dardania

Wearb wrote: »

Don't reduce your flow/return temperature too much, even condensing boilers have their minimum.

can screw up heat exchangers I believe?

Boiler manuals give their guidance...

Sleeper12

Even with trvs these will cost more money to run then correct sized rads. The bigger the rad the more water needs to be heated before your trv desides its hot enough in the room. There is a reason why plumbers calculate the right size rad.

Buy t correct size rad now and save money for years to come

after_shock3000

Thanks for the replies. I've since used a different calculator that takes into account more parameters and the rad sizes that it estimates are bigger.

Dardania wrote: »

often times with new installations, oversized radiators are installed to make the most of condensing boilers. The idea being that in order to get the return temperature to the boiler to allow condensation occur (where the real efficiency gains can be seen) for a given heat input to the room, you need to oversize the rad...

In your case, it should be fine, but just recalcualte your BTU outputs bearing in mind reduced flow and return temperatures. The old school (pre condensing boilers) way to calc was 82C flow, 71C return (suspect your BTU numbers are based on something similar) whereas with condensing boilers they typically look at 70C flow, 50C return (which needs a bigger rad to get the same heat output...)

Thanks for that, I checked up on it and recalculated. The values I had were based on ΔT 50°C and for condensing boilers it's closer to ΔT 40°C, which from what I can find gives about 75% of the heat output for the same size rad.


The only thing I'm unsure of now is if I've actually calculated the radiator size for the rooms correctly.
Most of the calculators seem to be based on newer buildings with concrete floors with soil underneath. My house was built in the 70's and has cavity block walls (although it will have external insulation) and it has wooden floors downstairs with an airgap underneath them.

I'm guessing this house is going to have a bit more heat loss that what those calculators are accounting for. That combined with the lower feed/return temps might mean these rads are closer to the correct size than I thought.

Can anyone point me to a calculator that would be accurate? Or a method of calculating it correctly myself?

Dardania

dT of 40C sounds okay. And good to hear you're externally wrapping the house - condensing boilers with oversized rads do best when they run for longer periods (taking advantage of thermal mass, which is wrapped presumably per SEAI requirement of 0.27 u value?)

The proper way to calc heat loss is: http://catalogue.segen.co.uk/reseller/docs/EN12831.pdf
Even allowing for the simplified example on page 66, it's a bit of a pig...

What sort of numbers are you getting?
And what's the ventilation and Windows / doors situation? Natural ventilation in all rooms (being done with the wrapping?) and new / old doors?

This one looks alright: http://www.myson.co.uk/hlm/terms.htm

MicktheMan

after_shock3000 wrote: »

My house was built in the 70's and has cavity block walls (although it will have external insulation) and it has wooden floors downstairs with an airgap underneath them.

I don't want to de-rail the thread but have you had the house tested for airtightness? All the external insulation in the world isn't worth a damn if the house leaks like a sieve. You might want to consider lifting the floorboards and insulating / air tightening the floor.

after_shock3000

Dardania wrote: »

dT of 40C sounds okay. And good to hear you're externally wrapping the house - condensing boilers with oversized rads do best when they run for longer periods (taking advantage of thermal mass, which is wrapped presumably per SEAI requirement of 0.27 u value?)

The proper way to calc heat loss is: http://catalogue.segen.co.uk/reseller/docs/EN12831.pdf
Even allowing for the simplified example on page 66, it's a bit of a pig...

What sort of numbers are you getting?
And what's the ventilation and Windows / doors situation? Natural ventilation in all rooms (being done with the wrapping?) and new / old doors?

This one looks alright: http://www.myson.co.uk/hlm/terms.htm

I'll be getting the wrapping done with someone that's SEAI registered for the grant, so I assume they'll have to hit the 0.27 value?

Ventilation wise the upstairs rooms currently have vents on the external walls, the downstairs rooms have vents under the floorboards on the external walls. Not sure what effect that'll have on the wrapping.

There'll be new double glazed windows and new internal and external doors also.

That pdf does looks like it'll take a bit of effort alright, I'll have a read over it. I tried the calculator that you linked to and it gave similar values for most of the rooms, some higher and some lower. I used 0.3 for the U value of the walls to estimate with.

The one room that changed massively was the living room. That calculator takes into account the open fireplace, while the others didn't.
That put the estimated rad for that room at around 7000 BTU instead of 4000 BTU. Room is around 4.1mx3.5m with a 2.6m ceiling. Window is 3.8m2 area.
Does 7000BTU sound reasonable for that room?

Dardania

MicktheMan wrote: »

I don't want to de-rail the thread but have you had the house tested for airtightness? All the external insulation in the world isn't worth a damn if the house leaks like a sieve. You might want to consider lifting the floorboards and insulating / air tightening the floor.

MTM is right - external wrapping helps alot, but there are still ways you're unintentionally losing heat.
You're never going to get it perfect, but hitting the main air losses is effort well spent...

A nice post popped up a few days ago on another forum about insulating under the floors - might be worth considering for sure:
http://www.boards.ie/vbulletin/showpost.php?p=98302700&postcount=2

If you want to go further, you can consider systems like the Aereco DCV

after_shock3000 wrote: »

I'll be getting the wrapping done with someone that's SEAI registered for the grant, so I assume they'll have to hit the 0.27 value?

Just be careful there - as long as you're doing it through the SEAI scheme (e.g. you've personally registered on seai.ie for it) they'll do the work to meet those requirements. Otherwise, if it's a private transaction, they'll be incentivised to cut corners...

after_shock3000 wrote: »

Ventilation wise the upstairs rooms currently have vents on the external walls, the downstairs rooms have vents under the floorboards on the external walls. Not sure what effect that'll have on the wrapping.

Upstairs sounds fine, albeit a traditional way of doing it, so there are going to be heat losses there. combination of heat input + air venting out to try keep the in-house moisture away...
With the downstairs, the underfloor vents may not be enough. The contractor has to, if following the SEAI scheme, ensure ventilation is adequate:
http://seai.ie/Grants/Better_energy_homes/contractor/Ventilation/

Just be careful that any rectification works they need to do are priced in the original quote, and ensure that there is adequate ventilation for rooms with stoves, fires, burners etc.

after_shock3000 wrote: »

There'll be new double glazed windows and new internal and external doors also.

A polite suggestion, if no-one has mentioned it already - seeing as you're putting in new windows & doors, and then wrapping - if you get the windows & doors installed flush with the outside surface of the house, it's a much easier install for the external insulation (they just overlap onto a small bit of the frame) and it'll result in better performance. I did it in my own house prior to wrapping, when we installing a front door - very elegant solution (and looks better from the outside instead of the sunken windows look...)

Fitting a letterbox / cat flap?

after_shock3000 wrote: »

That pdf does looks like it'll take a bit of effort alright, I'll have a read over it. I tried the calculator that you linked to and it gave similar values for most of the rooms, some higher and some lower. I used 0.3 for the U value of the walls to estimate with.

The one room that changed massively was the living room. That calculator takes into account the open fireplace, while the others didn't.
That put the estimated rad for that room at around 7000 BTU instead of 4000 BTU. Room is around 4.1mx3.5m with a 2.6m ceiling. Window is 3.8m2 area.
Does 7000BTU sound reasonable for that room?

In theory, you should be using 0.27 for the walls (the final solution per SEAI has to meet that) and there shouldn't be any heat lost to any adjacent properties if they're heated (the room temps are the same in theory, so no heat transmission)

The living space does feel a touch high, when I convert it into watts /m sq @ 140W/m sq (my thick electrical engineer's way of looking at things, back when I sized storage heating!)
With your fireplace, will that be left open all the time, or will you only occassionally light it, and likely put a balloon in the chimney up it? I would have expected something around the 100w/m sq number, particularly if you're wrapping & fitting windows.

after_shock3000

MicktheMan wrote: »

I don't want to de-rail the thread but have you had the house tested for airtightness? All the external insulation in the world isn't worth a damn if the house leaks like a sieve. You might want to consider lifting the floorboards and insulating / air tightening the floor.

Missed your post somehow. I haven't checked how airtight the house is but isn't some ventilation downstairs going to be necessary anyway after the insulation?
Would the venting under the floorboards be more than required?

Dardania wrote: »

Just be careful there - as long as you're doing it through the SEAI scheme (e.g. you've personally registered on seai.ie for it) they'll do the work to meet those requirements. Otherwise, if it's a private transaction, they'll be incentivised to cut corners...



Upstairs sounds fine, albeit a traditional way of doing it, so there are going to be heat losses there. combination of heat input + air venting out to try keep the in-house moisture away...
With the downstairs, the underfloor vents may not be enough. The contractor has to, if following the SEAI scheme, ensure ventilation is adequate:
http://seai.ie/Grants/Better_energy_homes/contractor/Ventilation/

Just be careful that any rectification works they need to do are priced in the original quote, and ensure that there is adequate ventilation for rooms with stoves, fires, burners etc.


A polite suggestion, if no-one has mentioned it already - seeing as you're putting in new windows & doors, and then wrapping - if you get the windows & doors installed flush with the outside surface of the house, it's a much easier install for the external insulation (they just overlap onto a small bit of the frame) and it'll result in better performance. I did it in my own house prior to wrapping, when we installing a front door - very elegant solution (and looks better from the outside instead of the sunken windows look...)

Fitting a letterbox / cat flap?



In theory, you should be using 0.27 for the walls (the final solution per SEAI has to meet that) and there shouldn't be any heat lost to any adjacent properties if they're heated (the room temps are the same in theory, so no heat transmission)

The living space does feel a touch high, when I convert it into watts /m sq @ 140W/m sq (my thick electrical engineer's way of looking at things, back when I sized storage heating!)
With your fireplace, will that be left open all the time, or will you only occassionally light it, and likely put a balloon in the chimney up it? I would have expected something around the 100w/m sq number, particularly if you're wrapping & fitting windows.

I will be going with the SEAI scheme, so should be fine there then.

I had heard of flushing the new windows with the outside of the building alright. There's a porch area outside the front door so that won't be flush but I'll likely add a sliding door on the outside after a while.
When I was getting quotes for the insulation I asked if it was ok to have the windows fitted flush and all but 1 thought it was a good idea.

100w/m sq is closer to the values that I got without taking into account the chimney, so sounds about right.
The fire will be lit rarely so those balloons look like a good idea.

gctest50

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MicktheMan

after_shock3000 wrote: »

Missed your post somehow. I haven't checked how airtight the house is but isn't some ventilation downstairs going to be necessary anyway after the insulation?
Would the venting under the floorboards be more than required?

Lack of air tightness (i.e draughts) and appropriate ventilation are not the same thing. You don't want the former and need the latter.

The subfloor ventilation has nothing to do with the house ventilation and that is why I suggested insulating and airtightening the floor. If this point is lost on you then do more research. A good starting point might be here.

after_shock3000

gctest50 wrote: »

one less hole in your house, an post are doing "Delivery Boxes":

Looks very handy, especially for parcels.

MicktheMan wrote: »

Lack of air tightness (i.e draughts) and appropriate ventilation are not the same thing. You don't want the former and need the latter.

The subfloor ventilation has nothing to do with the house ventilation and that is why I suggested insulating and airtightening the floor. If this point is lost on you then do more research. A good starting point might be here.

Cheers, I'll have a read over it.
From the draft side of things would sealing between the boards be a good improvement? Something along the lines of Draughtex or Stopgap
?
I'd prefer not to have the added complexity/cost of pulling up and insulating every t&g floor in the house unless its absolutely necessary.

MicktheMan

after_shock3000 wrote: »

Cheers, I'll have a read over it.
From the draft side of things would sealing between the boards be a good improvement? Something along the lines of Draughtex or Stopgap
?
I'd prefer not to have the added complexity/cost of pulling up and insulating every t&g floor in the house unless its absolutely necessary.

Imho, these product don't work over time and tend to get sucked up by the vacuum cleaner.
Yes it is added cost and hassle but if not done properly you may very well be sitting in your externally insulated house feeling draughts. Depends on what you want to achieve really.
Also, as you are getting new windows installed, you should investigate having the new window frames airtightened (special tape) to the walls (as well as moving them out flush with the outer wall)

Sleeper12

Also, as you are getting new windows installed, you should investigate having the new window frames airtightened (special tape) to the walls (as well as moving them out flush with the outer wall)

I don't know anything about pushing windows out flush to the wall but couldn't agree more about making them airtight. You can have the best windows in the world but they are useless if not sealed properly. I've actually seen curtains moving from the wind outside because they are not aritight