Is Mvhr worth it for me?

[Craig88]

Hi all, I keep coming back to this forum when researching mvhr so thought it would be a good idea to create an account and post a thread. 
 

I live in a 1930’s apartment block on the top floor with flat roofing, hence no loft. It’s a 2 bed 1 bath 55m2 square apartment with all the rooms basically off the same small hallway. It’s essentially not really airtight, there’s a big air brick in the kitchen above the boiler. Temperature wise it’s also cold. Now with London weather around the lower single digits(3c) the second bedroom struggles to

get above 20c with heating on all day and the bathroom only has a towel rail and is probably 17c. Living room is 19c and main bedroom is 22c as it has secondary glazing, is south facing and has the biggest rad. 
 

The previous owners installed a kair trakmaster mvhr which is about 10 years old and doesn’t seem to be helping much. The second bedroom is quite humid and is constantly getting mould on the ceiling. I was thinking of

upgrading it but it’s positioned in the second bedroom which means noise is an issue for the lodger in that room. The other issue is that they cored 100mm holes which means I’d ideally need to get the existing 4 holes cored to 125mm which is what it seems most units ducting size is the days. Which adds even more expense to the upgrade. 

I’m currently in the process of getting the windows replaced which is why I’m having to decide to either go for the passive ventilation option of having trickle vents installed and one continuous extractor fan in the bathroom or a new and better mvhr unit. I’m struggling to see if the cost of around 1,500-2,000 for unit and installation would ever pay itself back. My concern with passive ventilation is that it would make the cold apartment even colder if 2c air is constantly drifting into a room that struggles to stay above 18c when “airtight”. 
 

The other issue is that in summer it boils! Bedroom 1 will often be 30c at night and as it faces a busy road I have to keep the windows closed. Was thinking of getting acoustic trickle vents and having the bathroom fan on boost during summer might be one solution. 
 

any advice would be appreciated. 
 

Thanks

[SuperJohnG]

Whats your current heating system? Gas or electric?

 

That MVHR system should never have been installed IMO. Its not going to add any value if its not air tight. Secondly...the condensation issue is strange. Are their air bricks and MVHR in the second bedroom? 

 

In my opinion.  If you have mains gas, make sure heating is working OK and let it ventilate as normal as it should. Albrit you'll be wasting energy you won't resolve the issues without spending a lot of cash. 

 

Defo dont install Windows without vents, that will cause more issues. It sound to me like the existing MVHR may be causing most of your problems, likely pumping all your heat out and leaving condensation in bedroom two. Turn it off and see what happens.

[TonyT]

Hi Craig,

 

im also wondering about the heating type and how long you see yourself living in this   Building?

 

whats the floor to ceiling height, Incase you can add extra insulation to ceiling/walls etc maybe more cost effective to do this rather than upgrade the MHVR?

[SteamyTea]

My first thoughts were about the heating to.

Have you does a thermal model of the place.  This only needs to be a basic room by room model i.e. floor, ceiling, walls, windows/doors and temperature differences.

 

Finding the air leaks is the challenge, as there may well be air movement though the insulation that is already in place, which negates much of the purpose of insulation.  What some people call a plasterboard tent.

 

MVHR, in itself, is not a heating system, it is just a better ventilation system.

Your place is a little larger than mine, and any money spent improving heating and ventilation is realistically never recouped,  So look at other benefits i.e. improved air quality, warmer building, less outside noise.

[ProDave]

I find this thread a bit sad, and feel some "expectation management" is needed.

 

What you have is a 1930's building with little or more likely no insulation in any of the walls or the inaccessible flat roof structure. You have single glazed windows and haphazard ventilation.  The walls are cold due to lack of insulation and you are getting condensation and damp because of this.  This building epitomises much of the UK's dire housing stock, I have been there, done that, lived with damp and mould and high heating bills. Never again thank you.

 

What to do?  Well the new windows will help. At least you will be less likely to get condensation on the windows.

 

What is really needed is a complete re model of the building, ideally with external wall insulation and the roof re done with proper levels of insulation, but I doubt that is happening any time soon.  But that is what's needed and governments keep talking about grant schemes to help it happen so perhaps one day it might?

 

I doubt mvhr will really help in this case.  All you can do is make sure you properly heat the property and properly ventilate it. A dehumidifier may help reduce the moisture levels and cut down on the condensation. But if you can't get it warm you need bigger radiators etc so you can.

 

Seriously have a look at the new home insulation grants that keep getting talked about and see if anything offers the possibility of getting your building upgraded.

[Craig88]

Thanks for the replies. Just to update it’s gas heating to three rads in the 2 bedrooms and living room. Living room rad is definitely undersized.  Bathroom just has an electric towel  rail heater which obviously doesn’t do much. 
 

The windows are actually double glazing, just appear old and misted along with drafts from the seals missing rubber etc. 

 

I had a quick look and the epc is currently 44 sitting in the E category. The report did recommend “flat roof or sloping ceiling insulation”. The bathroom does have a lowered wooden ceiling which might have been done to make it less cold. 
 

Just to give you an idea of costs for December gas was £74, which is nearly double November as the lodger has been wanting it warmer. Electricity £50. He sets the thermostat to 21 in his room but it never really hits that so it’s generally on all day. Obviously this is the extreme being that we are all home 24 hours a day now as opposed to last year where I’d have it come on in the morning for an hour or two and then again in the evening after work for 2/3 hours. 
 

The ceiling is about 2.65m high. I had thought about ceiling insulation but was just a bit concerned about the risks of creating damp up there which seems to be one of the side affects of internal wall insulation. I had emailed a few companies about the green homes grant for insulation but never heard back. The main bedroom is actually fairly warm and is often 23/24 when the other bedroom is around 21 during higher single digit temperatures. I think the secondary glazing does help with the that. 
 

Perhaps the middle ground is just getting the windows done, adding trickle vents to them, and adding another radiator in the living room. Along with a continuous trickle extractor fan in the bathroom. 
 

The current air brick is in the kitchen and the window in the kitchen has one of those round spinny air vents which turns when I put the bathroom extractor fan on so I know that’s where the fresh is coming from. The mvhr is currently extracting from the second bedroom and hallway. I can try switching it off and seeing if that improves the problem. I know all about dehumidifiers as I currently have two and would run them continuously last year, although found it pricey on electricity. 
 

Thanks again for the ideas. 

[ProDave]

If you are going to try and re configure the mvhr, then is should be supplying fresh air into the living rooms and bedrooms, and extracting stale air from the kitchen and bathroom.  since you have it, you might as well try re piping it properly.  With the mvhr correctly piped like that, I would block up the air brick in the kitchen.

 

2.6M ceilings is good, I would be minded to put a false ceiling in at the normal height of 2.4M and get 150mm of loft insulation up there before the new plasterboard goes on.  It would also give you space to hide the mvhr ducting when re piping it.

[TonyT]

Is the boiler in the bedroom and that’s why it’s warm?

 

what about insulated plasterboard stuck to the wall in the style of Wookey on the green building forum?

[MJNewton]

10 hours ago, ProDave said:

If you are going to try and re configure the mvhr, then is should be supplying fresh air into the living rooms and bedrooms, and extracting stale air from the kitchen and bathroom.  since you have it, you might as well try re piping it properly.  With the mvhr correctly piped like that, I would block up the air brick in the kitchen.

 

I'd second this. You might as well make the most of the MVHR - it's a good method of ventilation (distributed, controllable) and does so with less energy loss than the alternatives. 

[Craig88]

I’ve actually requested a thermal imaging camera from octopus now to actually see where the weak spots in my insulation are. I did initially think it was the ceiling but after getting secondary glazing in the main bedroom I realized that room would heat to 23 when outside temperatures were around 8-10 which didn’t seem too bad. I was also able to heat the living room up to about 22 last night with outside temperatures around 1, when using an electric oil rad heater. Usually this room would be limited to 18/19 at the warmest. Which makes me think I need another rad in there, although not sure if the current boiler can handle that as it already struggles to heat them all up if they’re open. 
 

The issue with the current mvhr is that it’s really old and noisy on boost. Which was why I was thinking of upgrading it and then ducting to the bathroom and main bedroom. But most units require 125mm ducting so it becomes a whole new installation. And for some reason or other even when it’s on trickle(15m3) all the time extracting from the second bedroom that room still has an RH of above 60% most of the time and a lot of condensation on the windowsills. So the end result is that I’d need to spend probably in the region of 1k-2k for a new system including additional ducting. And then the question is whether that’s worth it for the energy savings or just to get trickle vents on all windows and have one extractor in the bathroom causing air to come through all the rooms continuously at a low rate?

[SteamyTea]

4 minutes ago, Craig88 said:

Which makes me think I need another rad in there, although not sure if the current boiler can handle that as it already struggles to heat them all up if they’re open. 

What is the size, and type of the current boiler?

5 minutes ago, Craig88 said:

most units require 125mm ducting so it becomes a whole new installation

You may get away with the current 100mm diameter pipe, just got to see what the flow speeds and volumes work out at.

6 minutes ago, Craig88 said:

And for some reason or other even when it’s on trickle(15m3)

15m³ what?

[SuperJohnG]

Something just not right if you can't heat the room with your boiler and radiators. Spec of this and size of the radiators would help. 

 

I'm inclined to say ditch MVHR. Get trickle vents on new windows, check boiler set up and radiator sizing, then install a fan in bathroom. But even at that just make it a normal extractor fan, but get one that closes when not on to stop heat leaking out. 

 

If you anted to do more than that you can start to look at adding insulation. 

[SteamyTea]

You can get single room MVHR units, they may be easier to install, may even be able to use some of the existing ducts with a bit of alternative thinking.

 

https://www.bpcventilation.com/vent-axia-tempra-p

[Craig88]

5 hours ago, SteamyTea said:

What is the size, and type of the current boiler?

You may get away with the current 100mm diameter pipe, just got to see what the flow speeds and volumes work out at.

15m³ what?

It’s a potterton suprima 30. Not really sure what the various measurements are but seems to be an output of 8.8 at max pressure. The three rads I have now are the old fashioned cast iron double column ones. Living room is 110x50, main bedroom is 160x75 and bedroom 2 is 90x90, which struggles to heat the room to 20 in current lower single digits. 
 

I’ve emailed a few of the smaller mvhr unit manufacturers like blauberg and they all seem to say they don’t recommend using 100mm ducting. I did think it might be fine provided I didn’t use it on boost although might invalidate the warranty.

 

I meant the unit now has a trickle speed of 30m3/hr  extraction rate which is currently split so the bedroom is getting air extracted at the rate of 15m3/hr. And even then it still gets condensation and mould build up. 
 

It does seem like a heating upgrade would be the best way to go about it. Considering if I was extracting from the bathroom now the temperature in there is only 16 so would be feeding 12c into the rooms with a lower end mvhr unit. 
 

I had considered getting a single room recovery unit. My only concern that having one in the bathroom and bedroom 2 would cost around 800 installed and there would be no ventilation improvement in the living room or bedroom 1 as they’d be in a vacuum. Whereas trickle vents in all rooms and one extraction point in bathroom would create a constant airflow in all rooms. 

[Craig88]

[DavidO]

On 31/12/2020 at 23:40, MJNewton said:

 

I'd second this. You might as well make the most of the MVHR - it's a good method of ventilation (distributed, controllable) and does so with less energy loss than the alternatives. 

I’m tending to agree with MJN/ProDave.....I wouldn’t give up on the existing MVHR unit too quickly; not familiar with the make but 10 years isn’t that old if it’s anything like a decent piece of engineering. Sounds to me as though it was very badly installed and that you have inappropriate configuration of the air distribution/extraction (rather than the unit itself) which might not be too difficult/expensive to sort in a 55msq 4 room property all on one level, even with 100mm ducting. 
Something else which is puzzling me is that you make no mention of condensate drainage from the MVHR unit? Is it possible that there is no drainage, or that the drainage system is blocked, and the (inevitable) condensate is accumulating in the bedroom and contributing to the mould problems you refer to in that room (and possibly/probably elsewhere)??