Heat loss/ rad sizing

[Jamesplumber92]

I've had two suppliers tell me they'll size the rads in a new build, the only info they want is the size of each room.
They said they don't need to know about windows, Insulation, what's above it or below as it's a new build.

I've heard that it's ok to oversize rads so that you can get a lower return temperature, do you think its safe to go with their offer?

 

[SJB060685]

If its a new build then the insulation levels should be a minimum standard. Is it a complete new build? Why don't you find out from the builders what the insulation is going to be and do a calculation yourself?

 

[Jamesplumber92]

If its a new build then the insulation levels should be a minimum standard. Is it a complete new build? Why don't you find out from the builders what the insulation is going to be and do a calculation yourself?

It's a bungalow that's been gutted and extended. The old walls have been given external insulation. The floors and ceiling are insulated too. Everything is up to building regs standards.

I know it would be good experience but a people have said it doesn't matter and that room size will do.
Just wanted to see what people think of that before I go putting work in

 

[ShaunCorbs]

These arnt accurate as they go off square footage / m3

 

[SJB060685]

These companies are probably basing that theory on a set standard of insulation but you will never get an accurate heat loss figure if the maths isn't done, either by hand or with software.

 

[Jamesplumber92]

These companies are probably basing that theory on a set standard of insulation but you will never get an accurate heat loss figure if the maths isn't done, either by hand or with software.

Well I made it through my apprenticeship without a measuring tape so I think I'll manage without measuring this

Cheers, I'll do it so. Stelrad calculator kept crashing but I got the cibses guides and that looks doable

 

[SJB060685]

At no point was what I said a jab at you buddy!? My point was these companies telling you that are not completely accurate, only a rough guess.
In your CIBSE book you will find pages and pages on known U values for varies walls, materials etc. From that you can easily work this out yourself like you say and arrive at an accurate answer.

 

[Jamesplumber92]

At no point was what I said a jab at you buddy!? My point was these companies telling you that are not completely accurate, only a rough guess.
In your CIBSE book you will find pages and pages on known U values for varies walls, materials etc. From that you can easily work this out yourself like you say and arrive at an accurate answer.

Oh I know, I was only making a joke

 

[SJB060685]

Oh I know, I was only making a joke

In that case I apologise. This is still for your oil boiler installation that's been the topic of several conversations recently?

 

[Jamesplumber92]

In that case I apologise. This is still for your oil boiler installation that's been the topic of several conversations recently?

Ya...won't be starting yet as the building isn't sealed fully. I'm just trying to get ready, I'm coming from the building sites so this is fairly new to me

 

[SJB060685]

Ok. Just remember that the return temperature for oil boilers has to be lower than that of gas boilers. The dew point for oil boilers starts around 47°c, as a pose to gas at around 57°c. This means that you will need to size the rads accordingly for the lower MWT of the emitters.

 

[Jamesplumber92]

Ok. Just remember that the return temperature for oil boilers has to be lower than that of gas boilers. The dew point for oil boilers starts around 47°c, as a pose to gas at around 57°c. This means that you will need to size the rads accordingly for the lower MWT of the emitters.

Will do, I'll be happy if I can get that right

 

[SJB060685]

If you're stuck on that I can go though it with you, that's no problem.

 

[Jamesplumber92]

Will do, I'll be happy if I can get that right

If you're stuck on that I can go though it with you, that's no problem.

Cheers, you're a great help!

 

[Jamesplumber92]

If you're stuck on that I can go though it with you, that's no problem.

There's one thing that's throwing me off. I've went by the cibses guide but it's saying I've more heat loss from the walk in wardrobe than the bathroom.

They're roughly the same size. According to the guide there's more air changes in the wardrobe than the bathroom.
That seems strange me, and the bathroom will be 4° warmer, you'd the think that the more heat there is the more to be lost to colder adjoining rooms and External walls.

Any insight on this?

 

[SJB060685]

If cibse says the air changes for walk in wardrobes is that then go buy that, especially as it's the type of room that needs aeration to prevent damp clothes etc.
When you're calculating the heat loss for fabric losses are you taking the adjoining rooms to be at design outside temperature (not sure whare you are in the country) or already at target temperature?

 

[ShaunCorbs]

Is there ventilation in the walk in wardrobe?

 

[SJB060685]

Is there ventilation in the walk in wardrobe?

I imagine so based on the whole house is being rebuilt but you raise a good point.

 

[Jamesplumber92]

If cibse says the air changes for walk in wardrobes is that then go buy that, especially as it's the type of room that needs aeration to prevent damp clothes etc.
When you're calculating the heat loss for fabric losses are you taking the adjoining rooms to be at design outside temperature (not sure whare you are in the country) or already at target temperature?

The adjoining rooms are taken as target temperature

 

[Jamesplumber92]

Is there ventilation in the walk in wardrobe?

Not at the moment. I doubt he's thinking of adding some, I'll flag it with him and see what he thinks

 

[SJB060685]

So any internal walls of the walk in wardrobe should be counted as no heat loss. Any external walls yes there is a heat loss.

 

[SJB060685]

Not at the moment. I doubt he's thinking of adding some, I'll flag it with him and see what he thinks

If there's no ventilation then it shouldn't have any air changes. So your cibse guide is not to be followed in this case.

 

[Jamesplumber92]

If there's no ventilation then it shouldn't have any air changes. So your cibse guide is not to be followed in this case.

Ok, it's down as 1.5 in the guide, not sure why

 

[SJB060685]

My only concern is the walk in wardrobe is not air sealed from the bedroom, therefore that may have an affect. Possibly allow for the air changes as per the bedroom in your calculations.