Garage Conversion - Big Heating Error

[morningbell]

Hi All,

We've almost finished a garage conversion, just the last snagging items to go.

Unfortunately, we've ended up in a situation where the plumbed in radiator is massively underpowered to heat the room. Clearly either we should have realised, or our builders should have advised that 1 radiator of 6200 BTU and a towel rail of 1000 BTU in the bathroom would not heat the space properly, but now we're in a situation where we have an almost finished garage, with walls plastered and painted, and flooring laid, where we need an additional heating source. I've seen a BTU calculator late in the day which suggests 11-12000 BTU would be needed to heat the room based on the layout.

I attach a floor plan, and 2 images (sorry for the mess!) of the garage. The intended use is as a multi purpose room, and also to use as an extra bedroom. It is around 25m squared with 6m square of glazing (skylight, patio doors, 2 windows).

I'm looking for some advice as to what might be the best course of action to take. We have 3 double plug sockets (marked by the "X" on my basic floor plan) in the room, which could take an electric radiator, or, would you advise the upheaval of plumbing another radiator in? I don't necessarily mind the upheaval of plumbing another in (the boiler could take it), but i'm at a bit of a loss as to know what to do.

Any pointers or advice greatly appreciated!

I can't see why plumbing in a larger radiator would be such a massive job?

You could mount another radiator back to back with the towel rail?

I suppose i'm thinking that there'd need to be another radiator plumbed in, rather than replacing the existing.

We did like the vertical modern style, but perhaps we do need to go functional to get the requisite BTU's.

Not sure given the space whether 2 radiators is the way to go over 1, even if the BTU is the same number.

Is there a radiator on the wall to the left? You could t off one in those rooms and have more radiators on the left hand wall.

But it sounds under insulated too for so much heat.

@RandomMess - thank you. I'm not sure how much difference the positioning makes in reality, but back to back with the towel rail puts it in the entry corridor, rather than the "main" portion of the room.

Just change the vertical radiator. We have some vertical columns radiators, the four column style give out loads of heat. It’s a fairly simple plumbing job.

Is the one already plumbed in double depth?

I have had double and single vertical radiators in various houses.

Also is the issue that the radiators are the last heat up when the heating comes on? If so you could turn down the thermostat on the other radiators and get the heating to come on earlier and stay on later?

@Rollercoaster1920 - no, the left wall and end wall are fully external, the right wall is fully external for half it's length, but attachesa to a conservatory which doesn't get heated often (even though it has a rad).

The room has been fully insulated (100mm Celotex in floors, walls and roof)

Where are you getting 11k btu from? I just popped your measurements into B&Q and got 6300 btu which is pretty much what you've got in your upright.

Rather than direct back to back with the towel radiator using the plumbing from there and feed it around the corner.

So surface pipes in the bathroom rather than showing in the main room

Fwiw we had terma electric radiators fitted in our loft conversion last year, and we've been really impressed with them

I'm not sure how much difference the positioning makes in reality, but back to back with the towel rail puts it in the entry corridor, rather than the "main" portion of the room.

As long as it doesn’t eat into the width of the corridor too much I can’t see why this would be a problem

@WhatsitWiggle - was using the calculator on bestheating.com

Measurements which total 25m squared of floor area, 2.3m height, 6m squared of double glazing, and the insulation, floor and external wall profile.

I’m not sure how you know it’s under insulated!
I am a bit confused as to why the door to the bathroom is where it is. That corridor seems odd. Does it lead to anywhere? If not, can you put a doorway across it at the top, thus reducing the space that needs heating and giving you a storage cupboard?

@Soontobe60 - there is a front door entry into the garage (so essentially i now have 2 entry doors at the front of the property 1 into our hall, 1 into the garage)

Once entering the garage, there is a corridor because the bathroom is immediately on your right hand side.

It is more like an annexe rather than a flowing extension into the house.

As for insulation, i couldn't say if it is under insulated or not, it has passed building control so assume it's up to scratch (100mm PIR in floor, wall and roof).

I'd check what calculations your builders have used as they won't have just made it up

When we had all our rads replaced last year, our plumber used 5btu per cubic foot and rounded up as we didn't think our living room one was big enough (it was, the old one was just rubbish).

It seems clear enough that the radiator isn't providing enough as the heat simply doesn't penetrate into the room. The builders said to wait until it was fully dry and ventilated before, which i have done.

We've got a smart heating system, so i can see the boiler effort is at maximum just to start getting the temperature up in there, and even then you can feel that it isn't penetrating the room.

I'm going to put some foil behind it to see if it makes a difference as well. But be good to keep hearing the suggestions as to what you would do with an extra radiator, if required (electric, plumbed, or just much larger one replacing existing).

We have a garage conversion and the towel rad in the bathroom in it is one of the first to heat up, the ones in the room part the last. It is very noticeable that the bathroom is toasty and the room never gets toasty until the evening!!

Our living room is bigger (maybe 35sqm) but similar amount of glass - we're semi detached so 1 shared wall, 2 outside walls and bedroom over part of it. We have about 13k BTU via 2 x 3 column vertical radiators. It's comfortable, wouldn't want any less (also had new boiler which is next to living room so think it's also the first room to get heating). I think 1 won't be enough and i'd get another radiator properly plumbed in - I'd speak to the builder about where is most convenient for plumbing.

Is that the biggest radiator of that style you can get?

We use best heating for all or rads and find the calculator to overestimate the BTUs needed, but not by much - we once went by a different calculator and regretted it and ended up replacing the offending radiator pretty quickly. We got an extra row and 3 extra columns and it did the trick.

We have a similar sized room in our house and we have the same radiator as you. However we do have 2, both doubles and the room is much warmer since changing to these from standard radiators. It wasn't a garage conversion though. It might not be as much mess as u envisage so def ask.

We did our garage conversion and the room has a double radiator that is very wide but it sometimes feel a bit cold too and it seems to get super hot in the summer 🤷🏻‍♀️

@Africa2go - really useful info thanks. That satisfies my cognitive bias that we don't have enough!

@Idontknowlondon - biggest in that style I can get is 7800 I think. To get 10k + from 1 radiator I'd have to lose some aesthetics

I’d lose the aesthetics. I’m Also mid way through renovations and every detail seems massively important but actually only you will really notice things that are less than perfect.

Remember though that carpets and curtains will also help you to retain the heat. It doesn’t sound like it will be enough but it will help.

@cloudtree - yes we will install curtains/blinds for the patio doors and skylight at some point which hopefully should help, although probably won't tip the scales in terms of avoiding needing the extra radiator output.

Have you checked the new radiator is heating up properly? Have the radiators been balanced since the new ones were connected? We have had to do a lot of tweaking to get our new radiators to put out the heat they are capable of.