Reliance Direct Vent vs FOGATTI Tankless Water Heaters: Key Differences

Why Venting Type Matters More Than the Tank

You’d think the water heater itself is the big decision. It’s not. The venting system determines what you can install, where you can install it, and how much it costs to run. This comparison pits a Reliance 40-gallon direct vent tank against a FOGATTI tankless on-demand unit. One uses sealed combustion with a dedicated intake and exhaust pipe. The other pulls combustion air from the room and vents through a chimney or flue.

If you’re replacing an old tank in a tight closet or a home with a leaky chimney, the venting choice gets real fast. The Reliance is a direct vent system, meaning it’s sealed from indoor air. The FOGATTI is a tankless unit that uses atmospheric venting—it draws air from the room and exhausts through a vent pipe. That difference changes everything about safety, placement, and efficiency.

I’ve installed both types. The first thing you notice is how different the installation process feels. Direct vent feels modern and contained. Atmospheric vent feels old-school and forgiving. But one of them has a hidden risk that most homeowners never think about until it’s too late.

Atmospheric Vent Water Heaters: The Traditional Chimney Approach

Atmospheric vent water heaters have been around for decades. They work on a simple principle: combustion gases rise naturally because they’re hot. The burner pulls oxygen from the room, burns the gas, and the exhaust flows up through a vent pipe, usually into a chimney or a dedicated flue. No fan, no blower, no electricity needed for venting.

The FOGATTI tankless unit uses this approach. It’s rated at 120,000 BTU and delivers 5.1 gallons per minute. That’s a lot of heat. But because it’s atmospheric, it needs combustion air from the room and a vertical or horizontal vent that can handle the exhaust. The unit itself is compact—23.9 x 15.5 x 7.3 inches—but the venting requirements aren’t.

Pros and Cons of Atmospheric Venting

Pros: Lower upfront cost, simpler installation, no moving parts in the venting system, works during a power outage (if you have a standing pilot). Cons: Pulls conditioned air from your home, can backdraft if the house is too tight, requires a chimney or flue that’s in good condition, and has lower efficiency because heat escapes up the vent.

The FOGATTI benefits from this simplicity. It’s CSA certified, has a copper heat exchanger and stainless steel burner. But the venting still needs to comply with local codes, and that’s where people get into trouble.

The Hidden Risk of Backdrafting

Backdrafting happens when exhaust gases don’t go up the vent. Instead, they spill into your living space. This occurs when the house is tightly sealed and exhaust fans (bathroom, kitchen) create negative pressure. The atmospheric vent can’t overcome that pressure, so combustion gases—including carbon monoxide—enter your home.

This is the safety issue that direct vent systems solve completely. The Reliance’s direct vent design seals the combustion chamber from indoor air. It draws air from outside and exhausts outside. No spillage, no backdrafting, no indoor air quality concerns. That’s a massive advantage for anyone with a modern, energy-efficient home.

Direct Vent Water Heaters: Sealed Combustion Explained

The Reliance 6-40-MDV400 is a 40-gallon direct vent water heater specifically designed for mobile homes. It’s 58-3/4 inches tall and 20 inches wide, with a 62 form factor and 2 inches of insulation. It uses a direct pipe system—one pipe brings outside air in, another exhausts combustion gases out. The whole system is sealed.

This design means the Reliance doesn’t compete with your furnace, water heater, or exhaust fans for indoor air. It also means you can install it in a closet, a bathroom, or a bedroom without worrying about combustion gas spillage. That’s a huge deal for mobile homes, where space is tight and ventilation is often limited.

How Direct Vent Systems Work

A direct vent system uses a concentric or twin-pipe setup. The intake pipe pulls fresh air from outside, and the exhaust pipe pushes combustion gases out. The combustion chamber is completely isolated from the room. This is called sealed combustion, and it’s the gold standard for safety.

The Reliance includes parts for natural gas and LP gas, so you can switch fuels without buying a new unit. It has an aluminum anode rod, which helps prevent tank corrosion. The 40-gallon capacity is standard for a family of three or four.

Pros and Cons of Direct Venting

Pros: No backdrafting risk, no indoor air quality issues, can be installed in tight spaces, higher efficiency than atmospheric vent, and doesn’t pull conditioned air out of your home. Cons: More expensive upfront, requires a side-wall penetration for the vent pipe, and the venting system adds installation complexity.

The trade-off is worth it for most people. The safety alone justifies the extra cost. But you need to check if your home has a suitable exterior wall for the vent termination.

Power Vent vs. Direct Vent: The Critical Distinction

People often confuse direct vent with power vent. They’re different. A power vent water heater uses a blower fan to push exhaust gases through a vent pipe. It still draws combustion air from the room. A direct vent system doesn’t use a blower (unless it’s a power direct vent, which combines both).

The Reliance is a direct vent, not a power vent. It relies on natural convection to exhaust gases. The FOGATTI is an atmospheric vent, which also relies on natural convection. So neither uses a blower. But the FOGATTI still pulls air from the room, while the Reliance doesn’t.

If you have a home with negative pressure issues, a direct vent is the safer choice. If you have a chimney that’s leaking or too small, a power vent might be better because it can push exhaust through a smaller pipe. But for this comparison, the key difference is sealed combustion vs. room-air combustion.

Direct Vent vs. Atmospheric Vent: A Side-by-Side Comparison

Feature	Reliance 40-Gallon Direct Vent	FOGATTI Tankless Atmospheric Vent
Venting type	Direct vent (sealed combustion)	Atmospheric vent (room air)
Backdraft risk	None	Possible in tight homes
Indoor air quality	Unaffected	Pulls combustion air from room
Efficiency	Higher (sealed combustion)	Lower (heat escapes up vent)
Installation complexity	Moderate (side-wall vent)	Simple (chimney or flue)
Space required	40-gallon tank (58.75″ H x 20″ W)	Compact (23.9″ H x 15.5″ W x 7.3″ D)
Fuel options	Natural gas or LP (parts included)	Natural gas only
Capacity	40 gallons storage	5.1 GPM continuous
BTU rating	Not specified	120,000 BTU
Power requirement	None for venting	120V AC for controls
Best for	Mobile homes, tight spaces, safety	Small households, on-demand needs

Which Vent Type Is Right for Your Home?

Your home’s construction and your water usage patterns decide this. If you live in a mobile home or a tightly sealed house, the Reliance direct vent is the obvious choice. It doesn’t need a chimney, and it won’t backdraft. If you have an older home with a masonry chimney in good shape, the FOGATTI can work fine.

But think about your hot water demand. The Reliance gives you 40 gallons of stored hot water. Once it’s depleted, you wait for the tank to reheat. The FOGATTI gives you endless hot water at 5.1 GPM, but only if your incoming water temperature is warm enough. In northern climates, cold groundwater can drop that flow rate significantly.

Retrofitting and Replacement Scenarios

Replacing an old atmospheric tank in a tight closet? The Reliance direct vent fits, but you’ll need to run a vent pipe to an exterior wall. That’s a bigger job than just swapping tanks. If you’re replacing a tank that used a chimney, you might be able to reuse the chimney with the FOGATTI, but you’ll need to check the vent size and condition.

For mobile homes, the Reliance is specifically designed for that application. The direct pipe system works with the limited space and ventilation of a mobile home. The FOGATTI, being tankless, is also a good fit because it saves space, but the venting needs to be done right.

Installation and Code Compliance: What You Need to Know

Venting codes exist for a reason. They prevent carbon monoxide poisoning and fires. For atmospheric vents, the code requires a minimum clearance from windows, doors, and air intakes. The exhaust can’t be near a bedroom window or a neighbor’s property line. For direct vents, the intake and exhaust must be separated by a specific distance to prevent cross-contamination.

The Reliance direct vent uses a concentric vent kit (not included) that simplifies this. The intake and exhaust are in one pipe, so you only need one wall penetration. The FOGATTI atmospheric vent needs a standard vent pipe, but it must be sized correctly and terminate above the roofline or through a wall with proper clearance.

If you’re a DIYer, the FOGATTI might seem easier because it’s smaller and lighter. But the venting code compliance is just as strict. I’ve seen homeowners fail inspections because their vent termination was too close to a window. Check your local codes before you buy.

Maintenance and Troubleshooting for Each System

Direct vent systems have fewer failure points. The Reliance has no blower motor, so the main issues are sediment buildup in the tank and a worn anode rod. The aluminum anode rod is a plus—it lasts longer than magnesium in most water conditions. You’ll need to flush the tank annually to prevent sediment from damaging the burner.

Atmospheric vent systems like the FOGATTI have more potential issues. The vent pipe can corrode or get blocked by debris. The burner can soot up if the air-fuel mixture is off. And because it draws room air, dust and lint can accumulate on the burner. The FOGATTI’s stainless steel burner resists corrosion, but it still needs periodic cleaning.

Diagnosing problems is different, too. If a direct vent unit fails, check the vent pipe for blockages or condensation. If an atmospheric unit fails, check for negative pressure in the house, which can cause backdrafting. A simple smoke test near the vent can reveal if exhaust is spilling into the room.

Frequently Asked Questions

Can I install a direct vent water heater in a bathroom?

Yes, direct vent units like the Reliance can be installed in a bathroom or bedroom because they’re sealed. The combustion chamber doesn’t draw room air, so there’s no risk of backdrafting. Just make sure the vent termination is at least 12 inches from any window or door.

Does a tankless water heater need a chimney?

No, the FOGATTI can be vented horizontally through an exterior wall. But the vent pipe must be the correct size and material for the BTU rating. It also needs to slope slightly downward to allow condensation to drain. Check the manual and local codes before installing.

Which is more efficient: a 40-gallon tank or a tankless?

Tankless units are generally more efficient because they don’t store hot water. The FOGATTI only heats water when you need it, so standby losses are zero. The Reliance tank loses some heat through the walls, even with 2 inches of insulation. But the efficiency difference depends on your usage. If you use a lot of hot water at once, the tank might be more efficient because it can deliver a high flow rate without waiting.

Can I switch from atmospheric vent to direct vent in an existing home?

Yes, but it requires running a new vent pipe to an exterior wall. That’s a significant retrofit. If your home has a chimney that’s in good condition, staying with atmospheric vent might be cheaper. But if you’re concerned about indoor air quality or backdrafting, the direct vent retrofit is worth it.

Final Verdict: Making the Smart Choice

For most people, the Reliance direct vent is the safer, more practical choice. It eliminates backdrafting, works in tight spaces, and is designed for mobile homes. The 40-gallon capacity is enough for a small family, and the direct pipe system simplifies installation. The only downside is the upfront cost and the need for a side-wall vent.

The FOGATTI tankless is a better fit for someone who wants endless hot water and has a suitable venting setup. It’s compact, efficient, and delivers 5.1 GPM. But the atmospheric venting means you need to be careful about indoor air quality and code compliance. If you have a leaky chimney or a tight house, it’s not the right choice.

Don’t skip the venting research. It’s the difference between a safe, comfortable home and one with a hidden carbon monoxide risk. Check the direct vent vs power vent guide for more details on other options. And if you’re leaning toward a direct vent unit, look at the best direct vent water heaters list for alternatives. For tankless troubleshooting, see cold water burst prevention tips.

At the end of the day, the Reliance is the sensible choice for most homes. It’s not flashy, but it’s safe and reliable. The FOGATTI is the fun one—endless hot water, small footprint—but it demands more from your home’s ventilation. Choose based on your house, not the specs.