gas-filed water heater venting ok after steam boiler removed? (converted to air-sourced heat pumps)

NYCDave

We recently converted our residential home heating system from a gas-fired steam boiler to air-sourced heat pumps. Now our only gas appliance is our 75 gallon hot water boiler. Previously, both the steam boiler and the hot water boiler vented into the same flue in our chimney (which is an outside chimney, three exterior walls above the 1st floor), but now it's only the hot water heater. I remember when we switched our boiler from oil to gas 5 years earlier, I read about how the new gas boiler may not heat the chimney enough and it could cause venting issues... now that it's only the hot water boiler, do we have to worry about venting issues? If the chimney does not get hot enough, will the CO still exhaust out the chimney properly? Thanks!!!

pecmsg

Too little information!
Water heater vent size?
Chimney size (ID)
Chimney height?
Exposed brick outdoors or all inside?

From here a liner is needed!

FWIW.............. should have kept the steam as back up!

WMno57

Why did you electrify your space heating, and not electrify domestic water heating at the same time?

ethicalpaul

Yes, rip that thing out and replace it with a Heat Pump Water Heater from Rheem or others, they are very good. Pity about losing the steam though.

Please share--are the heat pumps doing OK for you in NYC? Did they do OK in the recent cold snap? I would love to convert my mother's home in New Paltz from oil forced air completely to heat pump, but the current Carrier is pretty old and can't cut it under 25F

JUGHNE

I foresee the future need for additional pages added to heat pump I&O manuals.

Mod Con I&O and others have a requirement to test draft on orphan WH's when removing atmospheric burners from the mix.

Should this be a requirement for the electrification of heating systems?

pecmsg

JUGHNE said:

I foresee the future need for additional pages added to heat pump I&O manuals. Mod Con I&O and others have a requirement to test draft on orphan WH's when removing atmospheric burners from the mix. Should this be a requirement for the electrification of heating systems?

More pages that don’t get read!

NYCDave

pecmsg said:

Too little information! Water heater vent size? Chimney size (ID) Chimney height? Exposed brick outdoors or all inside? From here a liner is needed! FWIW.............. should have kept the steam as back up!

Water heater vent pipe is about 6 inches diameter. Chimney height is three stories plus extra 4 feet, so I would guess around 35 feet total. Exposed brick outdoors. we considered keeping the steam, but wanted to recover space from the radiators, and there were other issues, not worth going into here.

NYCDave

WMno57 said:

Why did you electrify your space heating, and not electrify domestic water heating at the same time?

We had to upgrade to 200 amp service just to accommodate the heat pump condensers. Adding another 50 amp circuit for an electric water heater would’ve required 400 amp upgrade, which was just too much for us.

NYCDave

ethicalpaul said:

Yes, rip that thing out and replace it with a Heat Pump Water Heater from Rheem or others, they are very good. Pity about losing the steam though. Please share--are the heat pumps doing OK for you in NYC? Did they do OK in the recent cold snap? I would love to convert my mother's home in New Paltz from oil forced air completely to heat pump, but the current Carrier is pretty old and can't cut it under 25F

These new heat pumps have some sort of inverter circuit that apparently makes them able to function down to -13°F. We had no obvious issues with the latest cold snap, with the lows around here getting down to about 5°.

NYCDave

JUGHNE said:

I foresee the future need for additional pages added to heat pump I&O manuals. Mod Con I&O and others have a requirement to test draft on orphan WH's when removing atmospheric burners from the mix. Should this be a requirement for the electrification of heating systems?

Nice to see some of the folks still here from when we did have our steam system, who helped me a lot in dealing with vents and skimming and all sorts of other fun stuff. That life is over for now though. I do think there should be some rules in place for the orphaned water heater situation. For what it’s worth, we have two carbon monoxide alarms in the basement and I have never had any of those go off, but I wonder if perhaps the exhaust could move partway up the chimney and then if it doesn’t get all the way out, it might leak at other levels of the house? 

JakeCK

NYCDave said:

WMno57 said:

Why did you electrify your space heating, and not electrify domestic water heating at the same time?

We had to upgrade to 200 amp service just to accommodate the heat pump condensers. Adding another 50 amp circuit for an electric water heater would’ve required 400 amp upgrade, which was just too much for us.

There is no way you would have had to upgrade to 400 amps for a hpwh. And most require 30amps, not 50. Some that are coming on to the market now are plugins that run off a 15 or 20amp circuit. Wth are you doing the to push you to the limit of 200 amps? How big is the house? How many heat pumps do you have and what is the amperage on them? Any other large appliances, 

Btw 200amps at 240v is 48,000watts. Assuming a COP of 2 that means you could be putting 327,000 btu's into that house. That's a lot of heat.

Mad Dog_2

At 5am I'm still waking up and can't see clearly enough to read my NFPA 54 charts, but 6" is probably a.little too big.  We did a very similar job 15 yrs ago that is STILL venting great. 4"  50 GALLON GAS WATER HEATER Flue went directly in to an insulated 4" SS liner all the way up and out
Mad Dog. .  

pecmsg

NYCDave said:

JUGHNE said:

I foresee the future need for additional pages added to heat pump I&O manuals.

Mod Con I&O and others have a requirement to test draft on orphan WH's when removing atmospheric burners from the mix.

Should this be a requirement for the electrification of heating systems?

Nice to see some of the folks still here from when we did have our steam system, who helped me a lot in dealing with vents and skimming and all sorts of other fun stuff. That life is over for now though. I do think there should be some rules in place for the orphaned water heater situation. For what it’s worth, we have two carbon monoxide alarms in the basement and I have never had any of those go off, but I wonder if perhaps the exhaust could move partway up the chimney and then if it doesn’t get all the way out, it might leak at other levels of the house? 

Be advised UL listed CO detectors Do NOT Alarm until 70 PPM is reached and exceeded for up to 3 hours!

Look into a NON-UL listed Low Level CO detectors. 1 near the boiler room 1 near the bedrooms. I like the Defender, there are others. These will alert @ 30PPM

WMno57

NYCDave said:

We had to upgrade to 200 amp service just to accommodate the heat pump condensers. Adding another 50 amp circuit for an electric water heater would’ve required 400 amp upgrade, which was just too much for us.

Thanks for explaining that. My home is the opposite of yours; Gas Space Heat and Electric HW. My 40 gallon electric resistance water heater has a 30 Amp 240v breaker. 100 amp service.
Water heaters are a form of energy storage. A Thermal Battery. If you could find a water heater with a large capacity in gallons, but a smaller breaker requirement (20 or 30), that might solve all your problems. It would have a longer recovery time, but maybe your hot water demands would fit with that.
If I were you, I would talk to another electrician. I would be surprised if your peak momentary electrical usage ever exceeds 48,000 watts. However, there may be a code limit for the total sum of breakers under a 200 amp main.

EBEBRATT-Ed

@NYCDave

The gas water heater goes by the "7Xs" rule for starters. So a 6" vent from the water heater would be 6x6=36 x .7854=27.28 square inches. The chimney area cannot exceed that by more than 7x so 7 X27.28=197 square inches

so in this example you chimney cannot exceed 12" x 16"


But that's just for starters it still has to draft ok and you may need a liner depending on if it is an inside or outside chimney

JUGHNE

The main electric load would be the back up heaters if any.
Do you have a ducted system with a single air handler with electric elements, if so how many?
Or what size breaker runs the air handler?

ethicalpaul

EBEBRATT-Ed said:

@NYCDave

The gas water heater goes by the "7Xs" rule for starters. So a 6" vent from the water heater would be 6x6=36 x .7854=27.28 square inches.

What is that formula you have there, Ed?

I was thinking it would be πr^2 or 3.14*(3*3) or 28.26 sq inches