Restoration Guide: HVAC Hot Water Heating

Editor's Note: This is article 10 of 16 in Chapter 8: The HVAC/Plumbing Guide of Old House Web's Home Restoration Guide. This guide was developed and edited for old homes from original materials in the U.S. Housing and Urban Development (HUD) Rehab guide.

10. DOMESTIC HOT WATER HEATING

Section 1--Introduction

Water heating is one of the largest uses of energy in a home, usually falling just behind heating and air-conditioning. If making your old house more energy efficient is one of your goals during your home restoration, then you should take a good look at your hot water heater, and decide whether rehabbing or replacing it might improve the energy efficiency of your home.

Section 10 of Old House Web's edited version of the HUD Rehab Guide HVAC/Plumbing volume takes a look at the various hot water heating systems you might find in an old house, and offers suggestions for improving the efficiency of the existing system, and the various options available if you choose to replace it.

Section 2--Hot Water Heating Systems in Old Houses

The type of hot water heater found most often in an old house is the storage type, where hot water is held until needed in a storage tank. The water is heated by electric elements in the water, a combustion burner at the bottom of the tank, or by a heat exchanger using fluid heated by another device such as a boiler. Storage tanks are normally sized to hold between 30 and 80 gallons of hot water, but larger and smaller tanks are available. Tanks are sized on the anticipated usage of hot water in the home, based on the number of occupants, and the number of plumbing fixtures using hot water.

Water heaters normally have a life span of approximately 10 to 15 years, although their lifespan can be increased with proper maintenance, such as replacing heating elements, and removing the accumulated sediment from the bottom of the tank. During your home restoration, you should examine the water heater, and make a decision on rehabbing or replacing it based on:

• How many years the tank has been in use--the month and year the tank was made is usually in its serial number.
• Whether you ever run out of hot water during normal usage. Take into account any new hot-water-using fixtures you may be adding during your home renovation, such as a whirlpool tub or dishwasher.
• How long it takes for hot water to get to the faucets when they are turned on, especially those at a far distance from the heater.

If you decide that replacement is the best route, you may want to consult with a plumbing contractor or mechanical engineer. Your first inclination might be to purchase the largest hot water heater you can, reducing the chance of ever running out of hot water. However, installing a tank larger than needed can be an expensive waste of energy. On the other hand, installing a tank that is too small can mean constantly running out of hot water.

Section 3--Options for Improving the Efficiency of an Existing Storage-type Hot Water Heater

There are several ways to improve the efficiency of your existing hot water heater. Wrapping blanket insulation around the heater itself can help prevent heat loss, but take care not to cover any vents, drains, flues, or combustible areas. Foam insulation can be used around the hot water line leaving the heater to also help prevent heat loss. You can install anti-convection valves or loops at the water inlet and outlet lines on the heater to prevent hot water from exiting except when needed.

3.1 Adding an Indirect Storage Water Heater

Your old house might have a hot water heating system that uses a coil in a boiler to heat the water. These systems are fine in the winter, when the boiler is also supplying heat to the home, but can be inefficient in the summer months. Adding a storage tank for hot water can reduce the number of times the boiler has to fire up during the summer.

3.2 Replacing Your Existing System with a New Electric Resistance Storage Hot Water Heater

Electricity is an expensive way to heat water, but if the home's daily use of hot water is average or below, an electric hot water heater can be convenient. They can be placed just about anywhere, and some of the newest models are leak proof. New units are also insulated quite a bit better than old heaters.

3.3 Replacing Your Existing System with a New Gas Storage Hot Water Heater

Families that use a lot of hot water might want to consider a new gas storage hot water heater. Gas is fairly inexpensive in most parts of the country, and new gas models are constructed to operate much more efficiently than older gas units. Gas units usually need to be vented, so you may be limited in where the hot water heater can be placed. There are gas hot water heaters available that have part of the unit outside the home, eliminating indoor venting needs.

3.4 Replace Your Existing System with a New Demand Hot Water Heater

A demand hot water heater only heats water as it is needed. It can eliminate the need for a storage tank, and can provide hot water immediately, rather than having to wait for hot water to arrive from the tank. These hot water heaters are available using either electric or gas--electric models have a lot of flexibility as to location, but gas units require outside venting. Demand hot water heaters can be used to supply hot water to the entire old house, or you can use small electric models in specific areas as a supplemental source of hot water.

3.5 Install a System to Supplement the Hot Water Heater While Remodeling

The engineering of domestic hot water heating has advanced, and there are several methods available to supplement an existing hot water system in your old house. A tempering tank can be installed, which allows water to warm to room temperature prior to entering the hot water heater storage tank. This reduces the amount of energy required to heat the water to a usable temperature. Solar panels can also be used to warm the water in the tempering tank. It is also possible to draw heat off of the air-conditioning or heat pump system of a home to assist in heating water. This method only works when the air-conditioning is in use.

There is even a system that can be used to take advantage of the hot water leaving through the waste lines of a home. Hot water in the drain system from a shower, washer, or dishwasher can be used to help heat new cold water prior to it entering the hot water heater.

3.6 Add a Heat Pump Water Heater (HPWH) While Remodeling

If your old house is in an area where electricity is the only option for powering a hot water heater, and you anticipate high hot water usage, you might want to consider a heat pump water heater. Heat pump water heaters heat the home's water without using expensive resistance heat except during peak usage times of the day. They are mostly used in warm areas of the country where freezing is not a problem, as they are normally located in garages and basements. The efficiency of the heat pump can also be reduced by cold temperatures. A drawback to these systems is that there are not many in use at this time, and finding a qualified installer or repairman might be difficult.