Why is my home so expensive to heat?

A couple recently moved into their 5 bedroom 1970s built home. We will call them Steve and Shamila (not their real names though).

Background info

The building:

• Walls are brick cavity aircrete (Celcon) with lightweight plaster. No cavity insulation.

 

• The windows and doors are PVCu and about 15 years old. Mock Georgian small paned windows. Patio doors in the lounge and another set in the dining room. No enclosed porch / lobby area. Front door hardwood and varnished with applied brush draught excluders.

 

• The central heating is an indirect gas fired boiler (that means they have a hot water storage cylinder with header tanks in the loft). Boiler age approx 15 years old wall mounted. About 50% efficient at best. Room thermostat, hot water cylinderstat, hard wired control system wall mounted in hallway.

• A pitched roof with concrete pan tiles covering. Trussed roof structure. Loft has been boarded out using sheet chipboard screwed to the truss tie bars / ceiling joists. Minimal, old fibreglass insulation visible near the eaves where the boarding had been finished. Looks about 50mm thick at best. 

• Solid ground floor

Furnishings: Fitted carpets and lightweight curtains left by previous owner.

The family:  The couple: both out at work all day. 2 Children at school age. No pets

The Problem

They have now lived in the house almost a year. Their heating bill for gas and electricity is  very   expensive. The previous owner had shown her bills and said that the house was warm and her bills were low.

The difference: One lady who lived in the house on her own as her children had left home. Her husband had recently died - reason for selling the large house. Most of the time the lady was either in her garden, or watching her tv in the lounge That was the main room that had the heating turned on apart from the hallway and her bedroom. Most of the other rooms had the radiators turned off. One person's washing and drying it on a clothes line. One person's use of water for the loo, showering, and the washing machine would be quite small.

In contrast: All the rooms had the heating turned on. The thermostat set at 22°C. 4 people's washing and mostly tumble dried. Some wet washing draped over a clothes horse in the kitchen whilst out at work.

4 people showering and using towels to dry themselves off. Mum and daughter both had long hair.

The Budget:

Steve phones to ask whether having cavity wall retro insulation is a good idea. He has a budget to keep to, but his heating bills are very high. He would like to make the most of any improvements.

Substantial savings are needed on the energy bills. They must be cost effective though.

Is it worth having cavity wall insulation retro injected?

It is a large detached 5 bedroom house. The first issue is humidity.

Water can also be in a vapour form. Still H2O and requires a lot of energy to heat it up. (There is another blog presenting the science). A house with all the windows and doors shut most of the time (the family are out all day) cannot get rid of the moisture.

What moisture?

1. 4 people breathing produces a lot of moisture. Ona very cold day you may notice the moisture coming out of people's mouths. That is happening 24/7. Where is that moisture going? Condensation on the windows? Soaking into all the soft absobant furnishings - the bed / mattress, sofa, curtains, carpets and so on. However, as the air in the house will probably be warmer than outside there will be a difference in air pressure. Air expands as it becomes warmer - if the walls and windows cannot move then the air will be pushed through the walls. The walls will become moist as the humidity condenses.
2. The 4 showers each morning and 2 in the evening have produced a massive amount of water vapour. Even with an extractor (their house didn't have an extractor in either bathroom or the ensuite) there is still a massive amount that goes into the house.
3. The cotton towels. They have just dried 4 bodies and 2 more for the girls hair. That is a lot of damp towels that will dry off during the day (if you are lucky). Where has all that moisture gone?
4. All the condensation on the walls of the bathrooms and ensuite. Left to dry off / evaporate whilst all the windows and doors are closed and the heating is turned off. (Daft heating the home is everyone is out of the house).
5. That washing hanging over the clothes horse in the kitchen. All that moisture evaporating off during the day.

Yes, if you collected all that moisture it would fill several pint glasses. Now consider heating that water to 22°C and maintaining that temperature. It would take a lot of energy. However, that is what is happening every day 365 days of the year.

The answer for stage 1

Drying the whole house out with a dehumidifier. Dry materials are easier, and therefore require less energy to heat up. Damp materials soak up energy. Wear a dry tee cotton shirt and you feel warm. Wear the same tee shirt when it is damp and you will feel cooler.

The air is in contact with most things in the house. The temperature of everything it is in contact with will become the same temperature - in equilibrium.

Dending upon the amount of humidity there has been in the house will determine how much water will need to be remove. Typically a house that has condensation on the windows will produce 2 to 6ltrs of water in the first 24hrs. Then, over about a week or so, the amount of water being removed will reduce down to nothing. At that point it will be about 40 to 45%RH.

If, after say 2 weeks of having the dehumidifier running it is still pulling out a significant amount of moisture then further investigation is required.

Stage 2 - Further Investigation

There are likely causes:

1. The extractors in the bathroom / shower room / ensuite / kitchen are not working (clogged up with lint and dust, or cooking fat)
2. Extractors not being used (Common issue in the summer when the light is not being used and the linked in switch to the extractor cannot work)
3. The rooms do not have extractors

Check if the cooker hood is an extractor or a recirculator. An extractor will have a vent that send the humid air during cooking out of the building. A recirculator looks very similar, but the air is directed through a filter and back into the kitchen. No humidity is removed from the room though. The filters are designed to catch airborne fat.

Stage 3 - Drying out towels after bathing 

It is surprising how much water is dried off our bodies and from our hair after bathing. As an experiment weigh the towels before you use them. [It is easier to put them in a bowl and used the kitchen scales]. Note the dry weight in grams. Then have your shower / bath. After drying yourself and hair, re-weigh the damp towels. Deduct the dry weight from the wet weight. 1 gram of water equals 1cc. There are 1,000cc in a litre.

Stage 4 - Moppingup the condensation

Using a high absorbant cloth, wipe down any condensation on the walls, and the shower and or bath. Wring the cloth out into a measuring jug.

Stage 5 - The assessment

Add the volume of water held in the towels to the water water in the measuring jug. All of that water will have become humidity within your home during the day and or night. It will have soaked into any soft furnishings such as the carpets, bed clothes, mattresses, sofas etc. The humid air will roll under furniture and condendense. It will also be at a slightly higher pressure than inside your cupboards, wardrobes and drawers as it will be warmer. The humid air will eventually pass through any gaps however small as it is in a gaseous state.

When the humid air cools the humid air becomes liquid and soaks into anything that is porous. That is why clothes in drawers and wardrobes can have mould growing on them even if they are shut in a wardrobe or in closed drawers. Furniture that has a wood content is an ideal food for mould growth as it is mainly carbon in the form of sugars.

Clothes that are particularly vunerable to mould include cotton, hemp, jute, and leather. When fabric conditioners have been used regularly a coating remains on the fibres. That is what is being slowly released as the 'fresh smell' they advertise. It has a high carbon content so is more food for the mould to feed on.

So what has all this to do with how much it is costing me to heat my home?

Dry materials generally are easier to heat up than wet ones. Water requires a lot of energy to increase its temperature. Evidence: Put on a damp tee shirt and then swap it for a dry one. The dry one will feel warmer as your body can easily heat the air between the fabric and your skin. The damp tee shirt will require more body heat to heat up the added moisture so you feel cooler. A wet tee shirt will require far more body heat.

The same as heating your home. A damp home will require far more energy just to heat the extra moisture.

What is the solution?

Remove as much of the additional moisture. That is the wet towels from bathing, drying washing indoors, and using extractor fans when cooking and in the bathroom / shower room. (Ideally with a 30minute over run).

It isn't worth putting an extractor on when boiling water in a kettle. However, using several pots and saucepans on a hob, or frying on a hob is worth using the extractor. The process of cooking includes freeing water molecules plus fats into the air. 'Oooh - that smells good!' can only happen if your sensors have contacted the atomised fats from what is cooking. The smell of freshly baked bread, or coffee wafting around the room. It is only the atomised fats and particulates that enable to smell to occur.

Humidity in the air is relative to dry air. It is measured as a percentage - such as 45%RH. That means the air has 45% more moisture than dry air. We need moisture in the air. Plants and animals need moisture. Even materials require some moisture. So we are not trying to go down to zero humidity. General day to day relative humidity should be about 40%RH. It can peak occasionally up to around 80%RH when someone has just had a shower or bath. However, it should go back to around 40%RH again reasonably quickly. That is the reason for taking the mositure out of the air.

What happens if the RH is lower than 30%RH? Your skin and eyes will notice it. Your skin will feel itchy and may start flaking as it is too dry. Your eyes naturally are lubricated every blink. The liquid wipes the ultra small particulates down into your tear ducts. Pollens, dust, airbourne spores and so on. The liquid also lubricates the surface under your eye lids. Very low RH and your eyes may feel tired and sore.

Relative humidity also reduces static electricity by constantly conducting it to Earth via the moisture. A really dry carpet made from wool and nylon, or just man-made fibres when in contact with othe similar materials such as sock and tight etc. As they contact the atoms / molecules collide and an electric charge is produced. Very small, but can build up if not constantly being Earthed. The consequence is when a person touched an item that can discharge the static electricity they can get a painful electric shock.

The solution:

If your home is going to be vacated most of the day it is likely to be made secure with locked doors and windows. To reduce the RH from bathing etc. and parhaps drying washing indoors (a problem if you are in a multi-storey housing especially). Use a dehumidifier with a laundry mode and timer.

Place the machine in the kitchen and use a clothes horse to drape wet towels or washing. The machine should be placed as recommended by the manufacturer so it removes the moisture into liquid form. When the RH in the room has reduced to about 40%RH the machine is designed to automatically turn off so it won't over dry the air.

Ideally, leave all doors to the rooms slightly open so the air can freely move about. When moisture evaporates into the air it diffuses. Diffusion of the H2O molecules will continue until eventually all of the air has an equal amount. The dehumidifier will be taking moisture continually so the whole dwelling will gradually be drying out.

There is more practical information in The House Buyers Handbook.