Using a Water Heater for Space Heating Part 2

Part 1 - see here

Efficiency / Cost

Unfortunately efficiency is a non-exact calculation and after much deliberation most of our customers go with a personality choice rather than hard numbers on how efficient they want their heat plants to be anyway. However, we will run through some numbers on cost to give you an idea of what you need to consider.

On the market in the hydronic industry there are usually 2 efficiency categories; high efficiency and standard efficiency. High efficiency units can rise as high as 95-97% efficiency. That means 95% of the heat you burned in fuel was transferred into the fluid of the heating system. Standard efficiency max out at around 85% efficiency. Such that 15 cents of every dollar spent on fuel go up the flue. So we all want to use the highest efficiency unit available right? Well, the cost of high efficiency units may make them cost more and run over the life of the unit than a standard efficiency one, but they come with a much higher initial cost.

Let's take a look at 4 different scenarios for our project house. I will be carrying the cost out to the life expectancy of a boiler at 20 years.

1. Tank style water heater dedicated to the radiant system, estimated life expectancy 5-7 years.

   Water Heater, 85% Efficient	$400
   Venting	$100
   Pump & Controls	$500
   Material Total	$1000
   Estimated Annual Fuel Cost	$2200 per year
   Lifetime cost at 20 years	$2200 x 20 + $1000 + $400 x 2= $45,800

2. Tankless Water Heater, estimated life expectancy 7-10 years

Tankless Water Heater, 85% Efficient, No standby heat loss	$700
Venting	$250
Pump & Controls	$800
Material Total	$1750
Estimated Annual Fuel Cost	$2000 per year
Lifetime cost at 20 years	$2000 x 20 + $1750 + $700 = $42,450

3. Tankless Water Heater, High Efficiency, estimated life expectancy 10-15 years

Tankless Water Heater, 95% Efficient, No standby heat loss	$1500
Venting	$100
Pump & Controls	$800
Material Total	$2400
Estimated Annual Fuel Cost	$1800 per year
Lifetime cost at 20 years	$1800 x 20 + $2400 + $1500= $39,900

4. Condensing Boiler, High Efficiency, estimate life expectancy 20-25 years

Condensing Boiler, 95% Efficient, No standby heat loss	$3000
Venting	$100
Pump & Controls	$500
Material Total	$3600
Estimated Annual Fuel Cost	$1700 per year
Lifetime cost at 20 years	$1700 X 20 + $2400 = $37,600

So we can conclude; if we carry out the costs of the systems to the same life span of 20 years

Water Heater, Tank style, 85% Eff with 7 year life expectancy, after 20 years	$45,800
Tankless Water Heater, 85% Eff with 10 year life expectancy, after 20 years	$42,450
Tankless Water Heater, 95% Eff with 15 year life expectancy, after 20 years	$39,900
Condensing Boiler, 95% Eff with 20 year life expectancy, after 20 years	$37,600

The higher efficiency units will cost less to run over extended time and an investment in a boiler will yield almost a 15% return on your money invested in a stronger heat plant. Initial costs on a boiler will be over 3-1/2 times that of a tank style water heater. But you do get what you pay for. Will your budget allow for an investment for an investment in a high power, long lasting, high efficiency power plant or do you need to tighten the belt and take a shorter life solution.

Tankless Water Heaters by Takagi. Designed for either Domestic Hot Water or Space Heating

Weil-McLain Condensing Boilers

Warranty

This is a bit of a throw away point for many customers but it needs to be considered. What warranty will you receive when using your heat plant for your heating system? Since Water Heaters are designed and built for domestic hot water distribution, the manufactures will write their warranties for that application. If you install a water heater for space heating, you will either void the warranty or decrease the warranty to about 1 year. Read the Warranty fine print.

Boiler Manufacturers are usually offering warranties on the boiler heat exchangers for 15-25 years (electronic parts are less). However, if you are do-it-yourselfer and expect to install your own boiler, again read the fine print, you may be voiding the warranty and have to pay for any replacement parts need from installation problems or breakdowns.