Tankless Furnace Integration is the Key to Energy Savings

What is a forced air furnace anyway? It’s just a big box with a fan in it, right? Right. It’s just a fan in a box with a flame-fired (direct-fired) heat exchanger. One way to get more mileage out of a furnace is to convert it to a hot water air handler using an efficient tankless water heater and some proper planning. When a furnace is converted, the burner, heat exchanger and gas valve are removed and a hot water coil, similar to a car radiator, is installed inside the box. The fan and some of the controls are retained, but otherwise the system is now without any combustion gases or flame whatsoever. This means the system is more safe and reliable; furnace flues and combustion air holes can all be eliminated, making the building more energy efficient simply by eliminating some huge sources of air infiltration. It also eliminates gas-fired heat exchangers that can create noxious gases.

After the conversion, when the thermostat calls for heat, a pump comes on and pumps water from the tankless water heater through the coil and back to the water heater. This circulation brings on the burners in the water heater, taking the temperature of the water up to 140-150 degrees. This is where the modulation I mentioned earlier really benefits the system. The burners will only produce the BTU’s needed to keep the water hot and no more. Then the fan on the “hot water air handler” comes on and produces warm air, just not as dry as that from a standard furnace. This gentler source of heat will likely never need maintenance, with the exception of fan servicing and filter replacement. The pump is a cartridge pump that is easily repaired if it fails. Heat is being produced at the efficiency of the tankless system and has little effect on the amount of hot water that is available for domestic use. This type of system solves many problems and means nobody will ever have to haul a furnace or water tank out of your basement again. Ever.

Tankless systems can even be used in hydronic heating situations, as replacement for old, inefficient boiler systems. Again, with full modulation, the efficiency of a radiant floor system or baseboard hot water will be greatly increased over a standard boiler. In many cases, space heat and domestic hot water can be integrated into one unit, if the unit is rated for space heat. If solar or geothermal is used as a pre-heat source, the savings can be tremendous. It is just a matter of proper design and load calculation. 

Going Tankless – Buyer Beware

While going tankless is a great idea no matter what the case, it’s definitely a “buyer beware” situation. I have seen many installations done by “professional plumbers” that were so far off the installation instructions they were in fact dangerous. Most tankless systems cannot utilize the existing water heater vent, require either sealed-combustion venting or additional combustion air, may require a bigger gas line, need a buffer-pipe for cold water sandwich alleviation, require a service manifold with ball valves and boiler drains and need specialized personnel to install them. Not to mention that educating the customer is the most important part of the job. Why?

When customers do not understand how tankless systems work, they may be disappointed. A water tank “thermally siphons” all the time, since the water is hot all the time. This means it takes less time for a water tank to deliver water, since a tankless system has to fire up first and get the water and the pipes hot. With a tank, the pipes are already hot. So longer lag times may be experienced. This problem can easily be overcome with a recirculation system like the Metlund D’mand system (http://gothotwater.com/). Also, tankless systems require a minimum flow to activate them, which means you may not be able to “trickle” water in the sink and still get hot water. Going tankless is the smart thing to do, but you need to know what to look for and how much it should cost. Be sure the system has at least a 3 GPM flow at a 70 degree rise at this altitude, or you may not get the flow you need. Also be sure the unit will protect itself from freezing, even if it’s inside. Believe it or not, a tankless system that isn’t freeze protected can freeze simply from the cold air dropping across the heat exchanger while the furnace is operating.

The Power of Modulation

Many people ask me how tankless systems work; in a word- modulation. The burners modulate up and down depending on how cold and fast the water is coming in. So if the water coming in is 40 degrees, it takes more gas to heat it up (so the burners modulate up) than it does if the incoming water is 60 degrees. Likewise, if only one sink is being used (roughly 1.5 gallons per minute or GPM) it takes less gas (so the burners modulate down) than it does if two showers are on simultaneously. Most tankless systems will easily handle two showers simultaneously at 40-degree incoming water at high altitude. Much more than that, and the result is that the water goes cold or the flow is decreased, depending on the brand of tankless system you install.

The wonderful thing is that those 2 showers can be taken forever! When your old water tank would run out in about 12 minutes, the tankless system will keep going and going and going. Sort of like that bunny on TV. And nothing feels as good as a clean, long shower, wrapped in the knowledge that it’s dead cold when you’re done and no energy is wasted. If you have a jetted or soaking tub, you’ll never fill it with a 50-gallon water tank. Even 2 tanks (think about that waste!) would have a hard time. By contrast, I fill my hot tub with my tankless system. That’s 330 gallons of water that’s heated by gas at 87% efficiency and I’m in my hot tub that night! Those who want to be part of the solution (but still want to have some luxury in their lives) have to go tankless. It’s the smart thing to do.

Space - The Final Frontier

I have seen some really big water tanks. The other day I was at a house in Boulder with two 75-gallon tanks that took up almost an entire utility room. Now none of their domestic hot water system is inside the house. The space we freed up by installing the units outside was tremendous. And the cold snaps that bring below zero temperatures are not a factor, with the internal freeze protection system of all the Tankless water heaters I recommend . Not all tankless systems are approved for outdoor use, however, so it’s best to consult the specifications. The great thing is that even installed inside they take up no space at all. They just hang on the wall waiting for someone to turn on a faucet. That’s how it should be. 

What the world knows that we don’t!

Tankless water heaters are proven technology around the world. The problem is they haven’t really caught on yet here in America. Elsewhere in the world, tankless technology is the only method of heating water, from point of use electric to whole-house gas systems. Most places in the world do not have the space or energy to waste on a tank of water that heats up constantly. Nor would it be conceivable to run out of hot water. Why pay to heat water over and over again at 60% efficiency when you can pay to heat it once at 85% and never run out? And why would you have a system that needs replacement every few years when you can have one that will last virtually forever? The fact is tankless water heaters are “component” systems, which means they have parts inside that work together to heat the water, all of which can easily and inexpensively be replaced when they fail. When your car needs a tune-up, you don’t rebuild the engine, right? Or your house needs a paint job, so you don’t call a demolition crew in to scrape it and start over! That would be absurd. The beauty of tankless technology is the replaceable parts, right down to the heat exchanger. That is what gives them 3 to 4 times the longevity of a tank.