Water Heating Systems

Chances are, your home has a hot water heater. While a cool shower is nice on a hot day, generally you want it hotter than that. Hot water will take between 20% and 1/3 of all the ‘heating’ energy consumption for a typical house – more in winter as the water from the ground will be colder – and we always have to be mindful of limiting water consumption, so it’s important to pay attention to hot water. Hot water can be as much of 50% of your entire water consumption.

Types of Water Heater

Hot water is stored in an insulated tank (typically 40/50/60 USGAL). As it is used, cold water enters the tank and then the heating system will engage in order to bring it up to the set point (49°C / 120 °F). The system cannot typically keep up with high usage, so your teenager (stereotype-alert) can and may well use all the hot water. Solve this problem by using an on-demand heater

Water Storage Heating

Hot water is only generated when it is needed and can be produced at a rate designed to keep up with your load (think one shower and one hot water tap simultaneously). Storage losses are therefore eliminated – typically 5-10% of the total energy loss with storage systems.

On Demand Water Heating

A relatively new technology for hot water generation is the heat pump. This uses an electrically-driven compressor to extract available heat from the air, ‘upgrade’ its temperature and then deliver it to water. By the miracle of the vapour-compression cycle, this moves more energy than you put in, resulting in an energy factor of over 3. These work really well if you have a hot water heater in a place with excess heat – say in a furnace room where the heating system is placed.

This AO Smith unit sits and quietly whirs away,

taking ambient heat and turning it to hot water:

4 units of hot water for each unit of electricity.

When the sun is shining, the solar system here feeds

straight into the tank and no electricity is used at all.

Heat Pumps

Condensing Models

Much of the heat (14%) lost goes up the flue in the form of water vapour (water in its gaseous form). If you can reduce theflue gas temperature, thus allowing that vapour to condense out, most of that lost energy can be returned to be used for water heating.

Condensing hot water heaters will likely be the more expensive models, but expect energy factors over 90% and big long term savings.

Gas

Efficiency depends on age, type. Older models – think of the ‘Power Vent’ concept – were produced with efficiencies in the low 60’s % and even newer ones have an Energy Factor (a measure of its conversion efficiency for typical usage) in the mid to high 60’s %. That means around 1/3 of all the energy you put into the system is wasted during the production and storage

Electric

Highly efficient (close to 100% heat transfer), losses related to the tank’s insulation. An Energy Factor of over 90% is typical.

Oil

Really this is just the same as natural gas with similar efficiencies, just with a different burner technology.

Solar

Renewable Energy

Further information

- Canadian government guide to water heaters

https://www.nrcan.gc.ca/energy/products/categories/water-heaters/13735

Powering your Heater

Using Your Hot Water

Appliances

Faucets

Flow rates are dependent on your task. One factor is whether you use water based on running it continuously – in which case low flow is good – or whether you use it to fill the sink, in which case you’ll get frustrated with really low flow fixtures with a long fill time. Really low would be defined at 0.5 USGPM (1.9 litres per minute), a good standard might be 2.2 USGPM (8.3 litres per minute).

Watch out for hot water sources being a long way from the point of use. With a really low flow fixture and a long pipe run, you will have to wait first thing in the morning for that pipe full of cold water to empty out – and the lower the flow the longer that will take.

Toilets

Whether you want to think about it or not, your toilet/W.C. is likely using more water than anything else. Generally the older the toilet, the more water it's using. Think: 1 second per litre of water consumed. If it's taking an age to flush, swirling around like whirlpool, that's likely costing you 13+ litres for each flush.

Dual flush toilets are the way to go - think 3 litres for a #1, 4.8 l flush for the other. If each house holder is flushing 4,5,6 times a day....these numbers really add up. Look out for potential incentives - these are often the subject of programs designed to conserve water at the municipal level.

Appliances Page

Shower

Usage:

A shower head is designed to defined flow rate, based on typical municipal water pressure (e.g. 45-60psi). A modern low flow shower head will consume in the region of 1.25 USGPM (4.7 litres per minute) per minute, but the sky is the limit with a multi-headed attempt to reproduce a waterfall in a rainforest! 2.5 USGPM (9.4 litres per minute) is still quite common as a defined ‘low flow’ standard but you can definitely go below that in a warm room.

Usage? The number that comes up again and again in research is a typical shower time of 6 minutes (interestingly the time an old friend said was the standard duration to smoke a cigarette…). If your parents were sent to a boarding school like mine, 2 minutes is more than enough.

Temperatures:

Our bodies really only like a narrow temperature range, close to but above our own body temperatures (38.4°C). Push it much over 40 and you’ll soon be jumping out.

Your experience of that temperature will be affected by the temperature in the bathroom, its relative humidity, and the amount of evaporative cooling. This effect is caused by the shower’s spray of fine droplets resulting in evaporation into the air. That energy has to come from somewhere and so the air’s temperature actually drops as a result. Once the ‘steam’ (there is never steam in your shower – it’s water vapour – tiny droplets) starts to be produced and your mirror’s misting up, you are at 100% relative humidity and so there’s no more cooling to be had.

Safety

Building Codes typically limit hot water storage to 49°C in single family houses, though hotter than that with an anti-scald valve in multi-residential applications, to eliminate concerns regarding Legionella bacteria. This is based on scalding risks. The hotter you store the water, the more actual hot water you have (as it’s almost always mixed with cold down to the required temperature), but the greater danger you have, especially with seniors or children.

Shower

Faucets

Toilet