Backdrafting 50 Gallon Gas Rheem Water Heater

[Themp]

I replaced our water heater a year ago with a Rheem conventional water heater. It's vent was shared with a gas 80 percent efficient furnace(electronic ignition), which uses a 8 inch flue chimney. The flue is a fired clay 8 inch tile and is dedicated just for the furnace and water heater. At the time of the water heater replacement I noticed that it would backdraft for around 30-60 seconds. I had the gas company come out and they tested everything for CO2 and it showed no leakage even when backdrafting. The gas tech person felt that this was acceptable and his only recommendation was to have a CO2 detector in the basement. I actually have them everywhere in the house. The vent is 16.5 feet of 4 inch type B to a 6 inch type B flue, 7 feet to the chimney. The chimney flue is 25-30 feet.

I just recently replaced the furnace with a 90 percent efficient one and therefore the water heater became orphaned(as they say) on the vent. It now backdrafts much longer, minutes now. It actually melted the plastic rings around the water inlet/outlet. So, I do need to correct this condition. My question is should I line the chimney with a metal liner, they did this for the furnace in attic that was replaced(it has it's own flue). Or go with a direct vent or power vent water heater. Not sure about a tankless at this point. I do like that we have hot water on a power failure. The direct vent water heater would have to be moved to where the basement utility sink is(horizontal vent would be to long for where the water heater is now) . I assume the power vent water heater could be where the current one is. Here are pictures of the the current setup:

https://www.dropbox.com/sh/eeqicw26t2r9egf/AABNa0-Tof_hmzx6wsoQ0kWJa?dl=0

Thanks for any comments, Tom

 

[Terry]

It looks like dowward slope on your venting for the water heater. I'm not surprised that it's back drafting. You may be better off with a water heater with a powered vent system. Be it a tank or tankless.
Tankless would give you some leeway for adjusting the height as they are smaller.

 

[Sponsor]

 

[Dana]

The burner BTU on that Rheem is...???

A 6" B-vent would be ridiculously oversized for a water heater, let alone an 8" tile flue under the best of conditions (ergo "orphaned") . The every ell in the 4" B-vent and the tee into the 6" adds some "equivalent length" to the horizontal run too, so you're looking at something like 16.5' + 7' + X'= at least 25' of horizontal before it has any vertical draft to work with in the chimney height. It probably backdrafted even when the 80% furnace was hooked up.

A 4" flue liner inside the chimney and replacing the 6" B-vent with 4" B-vent would at least give it a shot, but that's still a heluva lot of horizontal relative to the vertical. If possible, moving the water heater closer to the chimney with a much straighter shot of 4" B-vent (with more slope) to the chimney would be preferable.

If it can't be moved or if it turns out to be too expensive, weigh out the relative costs of either a power-vented gas burner or a heat pump water heater, despite the relative youth of the water heater. If you normally run a dehumidifier in the basement in summer to keep the musty-basement smell at bay, a heat pump water heater will provide a good chunk of that dehumidification, and usually costs less to operate than even a condensing gas water heater.

(It's water over the dam and under the bridge and out to sea already but...) In situations such as yours a condensing water heater and a hydro-air coil right-sized for the heating load usually works out pretty well, but would have needed to be considered before the new furnace went in, and impacts the AC if sharing the same ducts.

BTW: In the pictures where B-vent in contact with the wall insulation, as well as where it is in contact with the flex duct are code violations. Code requires a minimum of 1" clearance to combustibles and since insulation traps heat, the clearance where it penetrates the insulation requires that the 1" gap be maintained by a 26 gauge or thicker metal shield that extends at least 2" beyond the insulation. I'm a bit surprised (though not shocked) that the gas company guy didn't flag that.

 

[MACPLUMB]

The problem is the flue gas is too cold, It doe's not make enough heat to get up that COLD, COLD, Chimney,
that is why you need a POWER VENTED HEATER, Running up outside the house,
Master Plumber with a PHD in Water Heaterolgy

 

[Master Plumber Mark]

You just need to modify the elbow on the top of the heater......
if you take off the double walled elbow and just install a common elbow
you would probably gain about 4 inches of fall on the whole line.....

I am no t saying it will solve the problem but it might.....
with it having to climb up and then
back down at the elbow again is not good

 

[Themp]

All thanks for the input. Dana you replied on a previous thread about my furnace replacement and I used some of your suggestions on that. The current Rheem 50 gallon water heater is 38,000 BTU. So, at this point you all seem to like a power vent or heat pump water heater. I just looked at Home Depot and Rheem, they have a 50 gallon heat pump water heater for $1,299 - $350 Duke Energy rebate. A Rheem 50 gallon power vent goes for $970. So they are the same in price. I like the idea of the heat pump and dehumidification. I have a separate dehumidifier now running during the humid summer months. However, the heat pump will need a condensate drain. Both type of units will also make noise. I am also concerned on the heat pump, and getting warm air to work with. Basement is not conditioned, so in the winter it goes down to at least 50 degrees. I assume the heat pump can make this even lower.

So, why not a direct vent water heater, that I move to the corner of the basement to vent out the back wall of the house? Some re-plumbing here but not to bad. No noise, no condensate line, no temperature worries, less to break down.

 

[Themp]

You just need to modify the elbow on the top of the heater......
if you take off the double walled elbow and just install a common elbow
you would probably gain about 4 inches of fall on the whole line.....

I am no t saying it will solve the problem but it might.....
with it having to climb up and then
back down at the elbow again is not good

Thanks, I will give this a try and see what happens.

 

[Themp]

I did forget to ask on question about venting that I could not resolve from searching the internet. With the old furnace at 80 percent, it was connected to the 6 inch flue after the water heater vent. Since that has been replaced, the 6 inch side hole has been sealed off with a plug and tape. The question is, with the old furnace connected, did it not provide some air to the flue when not running. Meaning, with the water heater running and the furnace not running, did the gases rising in the flue pull air from the furnace. Now with it plugged off, no air can mixed with the water heater gases as it tries to get to the chimney. Does this make it worst or better, or just not a factor in venting?

 

[Dana]

All thanks for the input. Dana you replied on a previous thread about my furnace replacement and I used some of your suggestions on that. The current Rheem 50 gallon water heater is 38,000 BTU. So, at this point you all seem to like a power vent or heat pump water heater. I just looked at Home Depot and Rheem, they have a 50 gallon heat pump water heater for $1,299 - $350 Duke Energy rebate. A Rheem 50 gallon power vent goes for $970. So they are the same in price. I like the idea of the heat pump and dehumidification. I have a separate dehumidifier now running during the humid summer months. However, the heat pump will need a condensate drain. Both type of units will also make noise. I am also concerned on the heat pump, and getting warm air to work with. Basement is not conditioned, so in the winter it goes down to at least 50 degrees. I assume the heat pump can make this even lower.

So, why not a direct vent water heater, that I move to the corner of the basement to vent out the back wall of the house? Some re-plumbing here but not to bad. No noise, no condensate line, no temperature worries, less to break down.

Heat pump water heaters have gotten a lot quieter & more efficient over the past 10 years. The new Rheem's are quieter than some refrigerators.

They all work just fine at 50F and a bit cooler. If it's getting colder than that in your basement it's a symptom of chronic outdoor air infiltration, partially driven by the open flue (cap it!), but also all of the air leaks along the band joist & foundation sill seams, poorly sealing clothes dryer vents, etc.

Taking a semi-serious stab at air sealing the basement from the outdoors will cut down on summertime humidity issues too. But if you want to REALLY get serious about it, air sealing and insulating the foundation walls & band joists is a longer term investment in comfort & efficiency that has benefits year-round. Raleigh NC is on the warm edge of DOE climate zone 4, where the IRC code minimum would be R10 continuous insulation, or a 2x4/R13 studwall. The studwall approach with no foam board between the foundation & cavity insulation/studs comes with a lot of mold risk. The safer/better/easier approach is 1.5" foil faced polyisocyanurate strapped to the wall with 1x4s through-screwed to the foundation with masonry screws, hanging wallboard on the furring.

Even though the polyiso is only labeled R9, with a shiny foil facer next to a 3/4" air gap to the wallboard the performance is R10 (legitimately). The wallboard doesn't need to be painted- it's there as a code-required thermal barrier against ignition of the foam. The seams need to be taped with a decent foil HVAC tape (eg Nashua 324a, usually available in box stores) . The cut bottom edge of the foam should not rest on the slab or it can wick ground moisture even if the slab isn't obviously wet, but even 1/2" of air is a sufficient capillary break. Caulking the sill to the foundation, and all of the seams between the sill & band joist, band joist & subfloor etc) is important- they add up to more than all the window & door crackage combined in most houses. In your climate it would be safe to insulate the band joist with high-density batts (R21 fiberglass or R23 rock wool) carefully fitted.

Deep subsoil temps in your area are in the low 60s F, and with an air tight insulated foundation & band joist the basement temperatures will most likely idle along in the mid 60s in the dead of winter just off the jacket losses of the furnace and what's radiating down from the subfloor.