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Can I heat my house with a water heater? Or should I use a boiler?

Air Conditioner, Alternative Heating, Alternative Methods of Heating, Energy Efficiency, Flooring Installation, Floors, PEX, Plumbing - Directory, Radiant Heat May 2, 2014 Sonia


Our project house in Long Island can use a water heater for space heating under local building codes. Because the slab installations will require less than 140 deg F water, it is safe to use a water heater to heat the radiant slabs. We will also be installing 2 separate water heaters; one to supply domestic hot water and a separate water heater to supply the radiant floor.

domestic

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

Water Heater

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

Tankless Water Heaters

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

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

Weil-McLain boilers

Weil-McLain Condensing Boilers

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