Yes, most radiant systems get their hot water from either a normal water heater or a boiler, our homes hot water and heat are both provided by a high efficiency Rinnai — or “on demand” — tankless. The Rinnai RU98i uses considerably less energy than a tank-type heater and costs less to install than a boiler with a heat exchanger.
Heating With A Tankless
Tankless water heaters are a proven technology with a long track record for heating domestic hot water in Southern Ontario. Unfortunately few contractors in our area have experience using them for radiant or home heating with a tankless, and thus information about reliable system design can be hard to find.
We consider our home system more than worthwhile: During the three years we have had the system, heat and hot-water costs for two people have averaged around $20 per month.
It’s important to note that we have added additional insulation (R-35 walls, R-50 to R-60 in the roof) and our large windows help us take advantage of excellent solar thermal energy. When the sun is out, which it often is here, we barely need any heat at all during the day. On occasion we also supplement our homes heating with a wood stove, which we enjoy for both comfort and ambience.
Finally, we use a programmable thermostat that limits the temperature to 62°F in the middle of the day and at night, and 70°F from 6 to 8 a.m. and 6 to 10 p.m.
Tankless water heaters take up very little space, are extremely efficient, and offer endless hot water.
Despite the fact that the units are not commonly used for home heating, they’re an ideal heat source for this application because their output temperatures can be easily matched to the needs of the radiant or hydronic system. With a heating controller the Rinnai tankless can provide water of up to 180°F, which is more than sufficient for the 110°F to 120°F needed to run radiant system.
The economics of using a tankless water heater to supply both hot water and home heating are also quite attractive. Total cost for a system like this is around $5,000, this includes a tankless, labour, the PEX tubing, and various components, controls, and fittings.
You can use a tank-type water heater for a little less cash upfront but the extra cost of the tankless model will more than offset extra cost with its energy savings. Energy efficiency of a heating appliance is expressed as a decimal called its energy factor, or EF. A tankless water heater has an EF between .82 and .97, which means it converts 82 percent to 97 percent of its energy input to heat. Conventional tank type units have an EF around .59, so a good 40% of money you spend on heating is simple pumped out the exhaust pipe.