Renovating and extending 1970s house with warm air heating

[Gooman]

Hi!

 

We're buying a 1970's-built 3-bed detached chalet-style house in Bedfordshire. Apart from a lick of paint and a recent bathroom, it's pretty much unchanged since built:

• Gas warm-air heating (ducts, and lots of 'em) with electric immersion heater for hot water
• Parquet floors to lounge, hallway and dining room which needs resanding, filling and sealing (plus filling the gaps left when we remove the warm-air heating outlets)
• 1970s kitchen, including sliding-door cabinets!

 

Our aspirations are:

• Immediate - Convert current tiny utility and the end of the double-length garage into a new dining area flowing off the kitchen, plus new utility and (probably) downstairs shower room
• Immediate - Roof lantern and bi-fold doors onto garden in new dining area
• Immediate - Replace warm-air heating, ideally with something more environmentally friendly
• Medium term - New kitchen (self-fitted)
• Long term - Replace tiling on gable ends with cladding (possibly cement board e.g. Marley Eternit)

 

Challenges are:

• Three-gabled (T-shaped) chalet roof limits possibilities upstairs unless we put in dormers (which we don't have budget for and which would be tricky anyway due to multiple gables)
• No space to add a shower to upstairs bathroom unless we make the small bedroom smaller and so thinking of downstairs shower
• Existing ground-floor spaces are concrete floor with no inbuilt insulation
• Garage floor is about 6" lower and so when we raise floor we'll have to raise the roof too
• Extending heating to the converted area of the garage - warm-air ducts can't be extended (and we don't think we're fans of it anyway), so thinking of wet under-floor heating in conversion and replacing heating in rest of building with traditional wet rads
• Asbestos throughout (we've had a specialist survey) including soffits, boiler flue, roof tile underboard, boiler cupboard door, utility ceiling, Marley vinyl floor tiles in kitchen (only the last three of these areas are likely to be touched though)
• Budget for immediate stuff is £30k. Conversion could be £20k, leaving only £10k for heating changes.

 

Looking for:

• Bright ideas on heating. Keen on ASHP but as we need new rads could be beyond our budget. Might have to settle for modern combi-boiler
• Any genius insight or pointers to existing posts on any of the above!

 

[Mr Punter]

My experience with warn air heating is that it makes the air very dry, making ones eyes and skin feel itchy and uncomfortable.  Also the air tends to form currents rather than be distributed evenly.  If you could add humidity, this may be OK, otherwise you may want to replace with rads.  ASHP will be expensive to run if you do not improve airtightness and insulation.  Perhaps a combi boiler with rads is your best option.

 

As you have identified, the solid concrete floor will be a pain to insulate as you probably don't have enough ceiling height to do this without breaking out the concrete, but even 30mm Celotex overlayed with chipboard will make a considerable difference.

 

Blown bead cavity wall insulation is reasonably cheap and cost effective.

 

I am not sure what, if any, insulation is in the first floor ceilings, but if none, this will be and area where you will lose a lot of heat.  With the loft part  you can just add more loft roll but with the sloped areas you would need to strip the plasterboard if you want to add insulation.

 

All your Immediate items look doable with your budget and although a mile away from the standard of self build new builds it will be a great improvement on what you have.

[Gooman]

Thanks for the tips!
 

Have looked into Vacuum Insulation Panels (VIPs)  for insulating the concrete floor but it's looking very expensive. Celotex might be the way to go, though since the lounge is huge the cost of carpeting will also be high so we'll probably live with parquet and rugs for a while!

 

Forgot to mention wall and roof insulation - wall cavities are insulated. Roof is only 100mm insulation so one of my first jobs is to pad that out to 270mm (after adding lap vents as there's currently no loft ventilation). From looking in the loft, it looks like regular loft insulation has just been stuffed down the sloped areas behind the plasterboard - might be possible to remove that and slide Celotex board down from within the loft.

[TheMitchells]

we have warm air, heated by gas, and I love it.  its quick to warm up the house from cold, clothes dry overnight if placed near an outlet and we have not had any problems with dry air.  that could be due to the timber frame house as we dont suffer from condensation after showers too.  so dont be too quick to bin it.?

[Gooman]

I've heard that a lot. It is a new (in last 12 months) boiler too (Johnson & Starley J50) ... but the big problem is that we can't extend it to cover the garage conversion, plus we want to get away from the electric immersion heater for hot water.

 

It's possible we might just add a combi boiler for the garage conversion and hot water - we'll decide that when we've lived with the warm air heating for this coming winter.

[TheMitchells]

Our system also heats the hot water although we do have an immersion for the summer when the heating is off.  Good luck with the work - it all sounds exciting!  Dont forget to do a blog so we can follow the work,  especially with lots of photo's too.?

Edited July 29, 2019 by TheMitchells
I cant spell!

[Gone West]

23 hours ago, Gooman said:

Gas warm-air heating (ducts, and lots of 'em) with electric immersion heater for hot water

Sounds good. If you are going to significantly improve the insulation then the warm air heating could be at a lower temperature. We have a very well insulated house with warm air heating and find it works well.

[Ferdinand]

Gold Star for a comprehensive first post.

 

Aerogel for your floor if you cannot build up far?

 

Make sure the asbestos is done properly. Asbestos in a ventilation system got my dad we think ... and he was just the supervising architect.

Edited July 30, 2019 by Ferdinand

[Gooman]

Isn't Aerogel as expensive as VIPs?

 

There's definitely no asbestos in the vent system itself - the survey was outstandingly comprehensive and thorough. Only places it's present in the heating system are on the inside of the door of the boiler cupboard and in the cement flue in the loft. The cupboard door will be disposed of in one piece, and the flue in the loft will stay where it is.

[Gooman]

Thanks everyone for your suggestions so far. Any comments on the thoughts below would be most appreciated!

 

As we're adding rooms in the garage conversion we'll need to heat them. The warm air system can't be extended, so we either need to add another boiler just for those rooms, or replace the whole system.

 

We also need to insulate the solid concrete ground floor in the existing house, but can't afford to rip and replace. Existing ground floor is approx 74m2. We're probably just going to go with Mr Punter's suggestion of 30mm Celotex and chipboard. Given that, we probably shouldn't/can't go with an ASHP and rads but will just have to use a modern combi boiler.

 

The garage being converted has the floor 100mm lower - so not enough room for a reasonable level of insulation for UFH (from what I've read, 300mm is recommended). So we'll probably have to do rads rather than UFH, and I'll just use PIR/chipboard flooring panels to bring the level up rather than a concrete fill.

 

It's a shame. I'd like to be more environmentally friendly, but we a) have to live in this house while we renovate it and b) don't have the budget to go the whole hog!

 

[Rjwlb]

On 30/07/2019 at 09:17, Gooman said:

Isn't Aerogel as expensive as VIPs?

 

There's definitely no asbestos in the vent system itself - the survey was outstandingly comprehensive and thorough. Only places it's present in the heating system are on the inside of the door of the boiler cupboard and in the cement flue in the loft. The cupboard door will be disposed of in one piece, and the flue in the loft will stay where it is.

 
 

just curious if you had a refurbishment/demolition invasive survey or a management survey? I know this is a couple of years old but we’re in a similar situation at the moment. House built in 1977  and has old warm air heating system. We think the boiler cupboard and flue may have been replaced already but not sure about ductwork. Did you have the whole system out in the end or just the visible and accessible bits? Was it safe to just block off the ductwork you couldn’t get at? Thanks :) 

[Gooman]

We had a specialist asbestos survey from these guys: https://safety-surveys.co.uk/. This involved them taking invasive samples and having lab tests done.

 

We decided to keep the warm air system in the end - and we're glad we did! It works really well! It's a Johnson & Starley J50. No rads and *very* fast to warm up. None of the fears that others raised were realised - no dust circulation or dry skin or dry eyes. In terms of costs vs a traditional wet system it's hard to judge ... you could only really judge after having ripped it out and replaced it! But based on the increase in room size over our previous property, we think the bills are in-line with a wet system.

 

Long term, we think our best replacement option is some form of electric heating into a heat exchanger that uses the same ductwork. Johnson & Starley make such a heat exchanger (called the Aquair) which works with electric boilers or air-to-water ASHPs. But the ASHP output temperature is a lot lower (35-40deg) rather than the 80deg of a gas boiler or regular electric boiler and so may not be viable unless the technology changes. We also briefly explored connecting an air-to-air ASHP indoor unit directly to the ducting, but it seems the existing ducting is too small in cross section (esp. that on the ground floor in the concrete). Upshot is that until gas becomes much more expensive than electricity, we're probably staying with the gas boiler.

 

We haven't insulated under the ground floors. The main insulation focus so far has been from the top down. Loft insulation was fine. As it's a chalet-style roof, we have eaves cupboards and eaves voids and these were entirely uninsulated! So there's been a ton of Celotex installed there. As the heating system blows warm air in directly, insulating the floor wouldn't provide a fast enough RoI to be worth the hassle and expense.

 

Our biggest sources of draughts have been dealt with (new front door, new kitchen extension and resealing around all windows and patio doors). One important one is the combustion air supply for the boiler. Some newer warm air boilers draw their combustion air down the outside of the flue from the roof terminal, but ours was a little older. The combustion air was previously supplied by a vent in the outside kitchen wall, as the boiler cupboard is in the kitchen. This clearly worked well as there was a fierce draught into the kitchen! After consulting the boiler manufacturer and our heating engineer, we now instead have a 5" circular plastic duct from the outside running between the ceiling and the floor above directly into the boiler cupboard. Depending on your boiler engineer's interpretation of the regs, this may also require ducting into the return air plenum in the boiler cupboard.

 

One more point on the boiler - the timer control is very old fashioned, just being a 24 hour mechanical rotary timer. I've augmented this with a Wifi remote control that's integrated into our home automation system, so I can program different times on different days, as well as having it automatically turn off when we leave and turn on when we come home inside programmed times.

 

We're planning to have the cavity walls insulated (yep, I know, we should have prioritised that). One other thing to watch on 70's builds is that the ground floor sockets are often dropped down from the first floor ring main, with the drops in the cavities (although not current practice this is apparently fine, but when you have cavity wall insulation done you need to mention it to your installer as they have to use blown fibres rather than polystyrene beads). This means that your sockets are backing into the cavity air, and are a source of draughts! We've plugged the holes in the back boxes with sealant to solve this.

 

I would advise you to definitely live with the warm air system a little before you decide what to do with it. We're vary glad we did! If you have any other questions on it, I'd be more than happy to help.

[Ferdinand]

On 29/07/2019 at 12:58, Gooman said:

I've heard that a lot. It is a new (in last 12 months) boiler too (Johnson & Starley J50) ... but the big problem is that we can't extend it to cover the garage conversion, plus we want to get away from the electric immersion heater for hot water.

 

It's possible we might just add a combi boiler for the garage conversion and hot water - we'll decide that when we've lived with the warm air heating for this coming winter.

 

Can you look at something like the type of heat pump that just requires a single hole in the wall, and sits on the inside?

[Gooman]

7 minutes ago, Ferdinand said:

 

Can you look at something like the type of heat pump that just requires a single hole in the wall, and sits on the inside?

 

Yes ... but that would only supply one room at a time and is quite ugly/industrial looking.

 

We didn't go with the garage conversion in the end but extended the kitchen instead. We just used a 2kW thermostatically-controlled wall-mounted electric heater as a top-up for the extra space. It's only on for a couple of hours in the morning and evening, and the thermostat keeps the on-time low.

[Ferdinand]

1 hour ago, Gooman said:

Long term, we think our best replacement option is some form of electric heating into a heat exchanger that uses the same ductwork. Johnson & Starley make such a heat exchanger (called the Aquair) which works with electric boilers or air-to-water ASHPs. But the ASHP output temperature is a lot lower (35-40deg) rather than the 80deg of a gas boiler or regular electric boiler and so may not be viable unless the technology changes. We also briefly explored connecting an air-to-air ASHP indoor unit directly to the ducting, but it seems the existing ducting is too small in cross section (esp. that on the ground floor in the concrete).

 

Upshot is that until gas becomes much more expensive than electricity, we're probably staying with the gas boiler.

 

(I think) a modern (post 2005 since when they have been required aiui) gas boiler running at more than about 55C output temperature will not be in 'fully condensing' mode so will be running at an efficiency of 70%-90% rather than 90%+ 

 

Another 3 months, then .

 

Quote

 

We haven't insulated under the ground floors. The main insulation focus so far has been from the top down. Loft insulation was fine. As it's a chalet-style roof, we have eaves cupboards and eaves voids and these were entirely uninsulated! So there's been a ton of Celotex installed there. As the heating system blows warm air in directly, insulating the floor wouldn't provide a fast enough RoI to be worth the hassle and expense.

It sounds like a candidate for skirt or wing  insulation should you get the chance.

 

Quote

 

Our biggest sources of draughts have been dealt with (new front door, new kitchen extension and resealing around all windows and patio doors).

Do your ventilation fans have backdraft shutters or HR?

 

Sounds like a great story overall. Good stuff.

 

F

[SteamyTea]

Not read all the replies just yet.

So my 10 penyths worth.

Is there a problem with sound transmission with the current heating? Especially between rooms. 

There is nothing to stop you fitting a heat exchanger from an ASHP in the ductwork to replace current heat source.

Except one thing. Gas, oil, electrical and soils fuels have high combustion temperatures (which lowers the RH to practically 0%), ASHP start to loose their efficiency once over about 45⁰C.

So this would reduce the amount of energy the the system, as a hole can deliver.

 

If you cannot dig up the floor and fit a decent amount of insulation i.e 120+mm, then do what you can. The floor will always draw heat out of the place, but if you are only heating the air in each room, then the temperature differences are not huge, circa 12⁰C. UFH is closer to 25⁰C.

Edited October 26, 2021 by SteamyTea

[Gooman]

54 minutes ago, Ferdinand said:

 

(I think) a modern (post 2005 since when they have been required aiui) gas boiler running at more than about 55C output temperature will not be in 'fully condensing' mode so will be running at an efficiency of 70%-90% rather than 90%+ 

 

Another 3 months, then .

 

It sounds like a candidate for skirt or wing  insulation should you get the chance.

 

Do your ventilation fans have backdraft shutters or HR?

 

Sounds like a great story overall. Good stuff.

 

F

 

The Johnson & Starley warm air boilers modulate the heat output - they don't work on a traditional "on/off" thermostat, but rather one that provides a resistance that varies proportional to the room temperature. The boiler will start up in the morning on full, then start to back off the output temperature, then keep the fan running longer, and then just end up "blipping" every couple of minutes at low output to maintain the temperature. So it probably us in fully condensing mode by that time.

 

I hadn't heard of skirt or wing insulation ... might have been worth doing before we had our patio renewed! No chance now though.

 

No heat recovery. There's no backdraft shutter on the combustion air - you couldn't do that as it would affect the ability to pull enough air through (as confirmed by our heating engineer). But that's not an issue now the combustion air goes directly into the boiler cupboard. The heating mainly recirculates air - there's air-return vents in the lounge, hallway and landing.

[Ferdinand]

2 minutes ago, Gooman said:

 

No heat recovery. There's no backdraft shutter on the combustion air - you couldn't do that as it would affect the ability to pull enough air through (as confirmed by our heating engineer). But that's not an issue now the combustion air goes directly into the boiler cupboard. The heating mainly recirculates air - there's air-return vents in the lounge, hallway and landing.

 

I meant ventilation fans eg in the bathroom, of course ?. Sorry, should have said.

[Gooman]

1 hour ago, SteamyTea said:

Not read all the replies just yet.

So my 10 penyths worth.

Is there a problem with sound transmission with the current heating? Especially between rooms. 

There is nothing to stop you fitting a heat exchanger from an ASHP in the ductwork to replace current heat source.

Except one thing. Gas, oil, electrical and soils fuels have high combustion temperatures (which lowers the RH to practically 0%), ASHP start to loose their efficiency once over about 45⁰C.

So this would reduce the amount of energy the the system, as a hole can deliver.

 

If you cannot dig up the floor and fit a decent amount of insulation i.e 120+mm, then do what you can. The floor will always draw heat out of the place, but if you are only heating the air in each room, then the temperature differences are not huge, circa 12⁰C. UFH is closer to 25⁰C.

 

No, not noticed any sound transmission issues. But then there is only the two of us.

 

An air-to-air ASHP heat exchanger (ie the indoor unit) is the option that I'm told is a no-go as the existing ductwork is too small for the lower air temperature. The ground floor ducts are around 100mm square, whereas first floor is 100mm x 250mm.

 

J&S advised that air-to-water ASHP on their Aquair unit (which is designed for the existing  ductwork) is unlikely to provide enough heat.

So the only way that ASHP becomes viable is if the technology improved to provide warmer output.

The only other electric alternative is an electric boiler with the J&S Aquair (like this: https://www.electric-heatingcompany.co.uk/electric-boilers/warmair-heating-replacement/) - but that's likely to result in much higher bills on the current electricity vs gas tariffs. That may change if the government decides to incentivise electricity over gas by removing the levies on electricity and applying them to gas - which may happen under the current green initiatives - see https://news.sky.com/story/boris-johnson-looking-at-new-green-levies-on-gas-as-prices-reach-new-high-leaked-document-reveals-12423200 for details on possible changes to gas vs electricity pricing.

Edited October 26, 2021 by Gooman

[Gooman]

5 minutes ago, Ferdinand said:

 

I meant ventilation fans eg in the bathroom, of course ?. Sorry, should have said.

Backdraft shutter on the kitchen hood. No fan in the bathroom yet ... we just open the window. Bathroom reno is still on the to-do list!

[SteamyTea]

19 minutes ago, Gooman said:

The ground floor ducts are around 100mm square, whereas first floor is 100mm x 250mm.

So that will be an area of 0.01m² and 0.025m².

 

If you had an airlflow of 2 m.s^-1 then you can shift 0.07 m³ a second.

That is 252 m³ an hour.

In proper language, you will be moving around 300 kg.h^-1.

Air takes 1 kJ.kg^-1.K^-1 of energy.

So to raise your air temperature from outside temperatures to duct temperatures will take about 11,000 kJ, or 3 kWh every hour.  That is a power delivery of 3kW.  Not much.

 

Now I have no idea what size your house is, or how fast air moves in duct work.  2m.s^-1 is about 4.5 MPH.

[Gooman]

1 minute ago, SteamyTea said:

So that will be an area of 0.01m² and 0.025m².

 

If you had an airlflow of 2 m.s^-1 then you can shift 0.07 m³ a second.

That is 252 m³ an hour.

In proper language, you will be moving around 300 kg.h^-1.

Air takes 1 kJ.kg^-1.K^-1 of energy.

So to raise your air temperature from outside temperatures to duct temperatures will take about 11,000 kJ, or 3 kWh every hour.  That is a power delivery of 3kW.  Not much.

 

Now I have no idea what size your house is, or how fast air moves in duct work.  2m.s^-1 is about 4.5 MPH.

 

Me neither.

 

Although we have the heating turning off when we leave the house, it feels comfortable within less than 5 minutes of arriving home. My home automation temperature monitoring suggests that it's currently raising the lounge temperature from 17deg to 18deg in 15 mins first thing in the morning.

[SteamyTea]

4 minutes ago, Gooman said:

Me neither.

Start measuring or we will be like heating 'engineers', just guessing and voicing uneducated opinion.

Edited October 26, 2021 by SteamyTea

[Gooman]

1 hour ago, SteamyTea said:

Start measuring or we will be like heating 'engineers', just guessing and voicing uneducated opinion.

 

According to the boiler manual, at peak the fan should be pushing out 0.27 m³ a second

[Gooman]

1 hour ago, SteamyTea said:

 

So to raise your air temperature from outside temperatures to duct temperatures will take about 11,000 kJ, or 3 kWh every hour.  That is a power delivery of 3kW.  Not much.

 

 

 

External air is only used for combustion, not for circulation ... it's primarily recirculating internal air. So it just has to raise it from the current internal temperature to the desired temperature.