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Frequently Asked Questions about the Open Direct System

What is the Open Direct System?

  • The Open Direct System uses the same domestic hot water heater that makes hot water for bathing and laundry to provide space heating, too. Everything in the system is made of materials that are fit to drink from, and a plumbing detail prevents stagnation of the water in heat tubes during the summer when space heating is not required. For details of this system, see Open Direct System. By reason of its efficiency, cost, and simplicity, this is our preferred system.

How can a hot water heater make enough heat for an entire house?

  • Houses are more efficient than they used to be. Most houses that are being built today use more energy for domestic hot water than they do for heat. Most domestic hot water heaters don’t do anything at all for 22 hours out of the day. You can get a hot water heater in any size that you want.

How does the Open Direct System rate in terms of cost efficiency, energy efficiency and environmental friendliness?

Very high on all counts.

  • First, it is cost efficient . You will save thousands of dollars because you will not need to buy a boiler or furnace at all. The heat drawn from the floor preheats the water entering the hot water heater helping to reduce the gas or oil bill. You will get better use from the one heating appliance that you will have to buy, a hot water heater.
  • Second, it is more energy efficient because the standby losses of a boiler or furnace are avoided, something that can be quite significant. And the lower operating temperatures of a high quality domestic hot water heater means less heat goes up the chimney. The lower operating temperatures of a high quality hot water heater enable it to condense the flue gases to water to achieve efficiencies of up to 95%. This also provides limited free cooling in the summer to save on air conditioning costs.
  • Third, the Open Direct System can be designed to use solar energy initially or be readily converted to solar, the most environmentally friendly heat source on earth. The solar domestic hot water heaters available from Radiantec represent off-the-shelf, fully developed technology that is both reliable and cost effective.

How does the cooling feature work?

  • It works by means of a zero cost plumbing detail which causes cold water to flow through the in-floor tubing before entering the domestic hot water heater to replace domestic hot water that has been consumed. This feature provides three important benefits of which free cooling is just one:
    1. During any period of high demand, priority is given to domestic hot water use.
    2. Cold water passing through the in-floor tubing draws some heat from the floor which provides some cooling and can save on air conditioning costs.
    3. The heat drawn from the floor preheats the water entering the hot water heater helping to reduce the gas or oil bill.
  • The installation of a $75 diverter valve will allow all water to pass through the in-floor tubing in the summer months and divert the flow of cold water only during the winter months.

How much cooling will I get?

  • If you have significant cooling needs, you will still need air conditioning, but this free detail can lower your air conditioning costs by $100-200 per year depending upon the amount of water usage, temperature of the incoming water, electricity costs. This effect works well because of water’s high heat capacity, the fact that it take a lot of energy to change its temperature. In fact, water’s unique structure allows it to store five times as much heat as concrete.

Isn’t it inefficient to cool the floor during the heating season?

  • No, because the domestic hot water heater gains any heat that the floor loses. Normal hot water consumption will not noticeably cool the house, and the thermostat will cause the heat to be replaced after the domestic hot water demand has been met.

What about condensation during the summer months?

  • Because the tubes are enclosed within the floor, humid air does not reach them and condensation will not occur. You will not get enough cooling to present a “whole house” moisture problem. In an extremely humid climate, air conditioning will be required and this will help to dehumidify the air as well.

How Large a hot water heater will I need?

  • 50 gallons of storage is probably adequate for most households, but heating output is more critical than storage capacity. The heating output of the unit must be equal to the amount of heat that the building will lose under the coldest conditions. Manufacturers provide heating output information for each model. The Polaris water heater has an output between 95,000 and 194,000 BTUs/hour depending on the model you choose.
  • Click here to read more about hot water heaters.

What are the disadvantages of the Open Direct System?

  • We can’t think of any other than the fact that in some areas, local codes have been slow to recognize the benefits of this newer and more advanced technology.