New Heater concerns

[Nicholas Roe]

Hello

I have a water heater from 1994 that is leaking. I live in Charlotte NC. I’m thinking about going tankless. My concern is that it would be in my crawl space. Fully enclosured crawl space. I have plenty of room all around the tank currently and I don’t really want to move it inside as there isn’t a good spot for it. Most electric tankless are for inside installation it seems. Currently Pex throughout the house. Haven’t had a issue with freezing as it very rarely gets that cold. Small house, small demand. No kids.

So 1: would it be ok putting a Rheem RTEX-13 in a crawl space? Or a something similar to that one.

2: if freezing is a concern can I just put it in inside a enclosure?

3: would it perform ok down there?

4: anything else I should consider?

 

[Dana]

An electric tankless is underpowered for your wintertime incoming water temperatures, as well as a power-grid abuser, gulping enormous amounts of electricity while in use, putting a strain on your local power grid infrastructure. (You can even see the powerlines jump when you crank the hot water suddenly to the maximum.)

In the winter your incoming water temperatures can drop into the low 40sF, but lets say it's never coming in colder than 45F. A 105F shower is a 60F rise, a 110F tub fill is a 65F temperture rise.

At max power the RTEX13 delivers 13,000 watts, or ~44,000 BTU/hr. At 2 gallons per minute shower at a 60F temperature rise to the shower takes 60,000 BTU/hr. That's about 18,000 watts. With an ultra low-flow showerhead 1.5gpm or less or an 18,000 watt or larger tankless you might just make it with the Rtex 13 but filling a tub would be an exercise in tedium, and it's not a whole lot better with an Rtex 18. The -18 draws 75A of 240VAC, and you'd need a dedicated 100A breaker to have any margin, and wiring heavy enough to pull the F-150 out of the ditch with the tractor. Do you even have sufficient electrical service for another 100A/240VAC?

In a sealed conditioned crawlspace freeze-up isn't a big risk in your climate, but it's still worth air sealing and insulating the crawlspace walls to keep the crawlspace temperatures high enough to not accumulate moisture in the floor joists or subfloor over the summer. The easiest way to (nearly) hit IRC code-min performance is to install 1.5" of fire rated Dow Thermax polyiso on the walls & band joists, taping the seams with temperature rated aluminum duct sealing tape. (That would also eliminate the freeze up risk until the next ice age, and lower the heating bill in winter.)

 

[Sponsor]

 

[Nicholas Roe]

An electric tankless is underpowered for your wintertime incoming water temperatures, as well as a power-grid abuser, gulping enormous amounts of electricity while in use, putting a strain on your local power grid infrastructure. (You can even see the powerlines jump when you crank the hot water suddenly to the maximum.)

In the winter your incoming water temperatures can drop into the low 40sF, but lets say it's never coming in colder than 45F. A 105F shower is a 60F rise, a 110F tub fill is a 65F temperture rise.

At max power the RTEX13 delivers 13,000 watts, or ~44,000 BTU/hr. At 2 gallons per minute shower at a 60F temperature rise to the shower takes 60,000 BTU/hr. That's about 18,000 watts. With an ultra low-flow showerhead 1.5gpm or less or an 18,000 watt or larger tankless you might just make it with the Rtex 13 but filling a tub would be an exercise in tedium, and it's not a whole lot better with an Rtex 18. The -18 draws 75A of 240VAC, and you'd need a dedicated 100A breaker to have any margin, and wiring heavy enough to pull the F-150 out of the ditch with the tractor. Do you even have sufficient electrical service for another 100A/240VAC?

In a sealed conditioned crawlspace freeze-up isn't a big risk in your climate, but it's still worth air sealing and insulating the crawlspace walls to keep the crawlspace temperatures high enough to not accumulate moisture in the floor joists or subfloor over the summer. The easiest way to (nearly) hit IRC code-min performance is to install 1.5" of fire rated Dow Thermax polyiso on the walls & band joists, taping the seams with temperature rated aluminum duct sealing tape. (That would also eliminate the freeze up risk until the next ice age, and lower the heating bill in winter.)

I would have to double check the power concern. I know I have 200A service.

So a tank would be more cost effective in a crawl space? Or should i try to find a place inside? Or switch to gas?

 

[Dana]

You have 200A service, but how much of that is already taken up by existing circuits?

If you can get a tank in the crawl space it lowers the freeze up risk compared to putting it outside, since none of the plumbing will be exposed to the outdoor air, and completely inside the house. There are several "lowboy" electric tanks out there. How wide is the access hatch/door, and how much vertical between the crawl space floor and the joists above?

 

[hj]

An "adequate" heater could take 120 amps.

 

[Nicholas Roe]

You have 200A service, but how much of that is already taken up by existing circuits?

If you can get a tank in the crawl space it lowers the freeze up risk compared to putting it outside, since none of the plumbing will be exposed to the outdoor air, and completely inside the house. There are several "lowboy" electric tanks out there. How wide is the access hatch/door, and how much vertical between the crawl space floor and the joists above?

Full size door and 6 foot all the way around the heater. I have a full size upright 40 gallon in there now. Plenty of spaces around the unit as well.

 

[Phog]

If you can switch to gas, why not do it? I see you mention the possibility. Just curious, it's almost always (a lot) cheaper per joule of heating to use gas.

 

[Dana]

If you can switch to gas, why not do it? I see you mention the possibility. Just curious, it's almost always (a lot) cheaper per joule of heating to use gas.

The installed cost of running gas plumbing and the higher cost of the gas water heater may never "pay off".

Given that there is 6 feet of headroom, installing a 50 gallon heat pump water heater (about 5 feet tall) would cost about as much as installing a gas water heater, draws less peak power than the existing water heater, would use about 1/3 the kwh, and would dehumidify the crawlspace, lowering the mold hazard (turning the latent heat of vaporization into heat stored in the tank.

BTW: In the US gas is usually billed in therms, decatherms, or CCF, not joules.

 

[Nicholas Roe]

If you can switch to gas, why not do it? I see you mention the possibility. Just curious, it's almost always (a lot) cheaper per joule of heating to use gas.

I have a gas meter at the house already so I don’t know how it would cost. Also I would need to put in a vent for it as well right?

 

[Nicholas Roe]

The installed cost of running gas plumbing and the higher cost of the gas water heater may never "pay off".

Given that there is 6 feet of headroom, installing a 50 gallon heat pump water heater (about 5 feet tall) would cost about as much as installing a gas water heater, draws less peak power than the existing water heater, would use about 1/3 the kwh, and would dehumidify the crawlspace, lowering the mold hazard (turning the latent heat of vaporization into heat stored in the tank.

BTW: In the US gas is usually billed in therms, decatherms, or CCF, not joules.

Thank you very much for your help. I really appreciate it. I will have to look in a heat pump tank.

 

[Dana]

I have a gas meter at the house already so I don’t know how it would cost. Also I would need to put in a vent for it as well right?

Running gas lines to the water heater space doesn't happen for free, even if you already have gas service to the house. You already have the electric service sufficient for a heat pump water heater in place.

Yes, a gas water heater would require a vent. A power vented gas unit can use cheap plastic venting and could be side-vented through a wall, but the power vent blower is usually on top, and adds to the height- you probably don't have enough headroom. A condensing tankless gas water heater could work, but may require upgrading the gas meter if you have other high BTU loads on it. In most cases it requires running a dedicated 1-1/4" gas line between the water heater and meter, with no tees off to other appliances.

There are rebates available in NC for installing a heat pump water heater, but may only apply to replacing electric water heaters or new construction. There are a variety of incentive programs run by different utilities at different rebate levels.

 

[Nicholas Roe]

Running gas lines to the water heater space doesn't happen for free, even if you already have gas service to the house. You already have the electric service sufficient for a heat pump water heater in place.

Yes, a gas water heater would require a vent. A power vented gas unit can use cheap plastic venting and could be side-vented through a wall, but the power vent blower is usually on top, and adds to the height- you probably don't have enough headroom. A condensing tankless gas water heater could work, but may require upgrading the gas meter if you have other high BTU loads on it. In most cases it requires running a dedicated 1-1/4" gas line between the water heater and meter, with no tees off to other appliances.

There are rebates available in NC for installing a heat pump water heater, but may only apply to replacing electric water heaters or new construction. There are a variety of incentive programs run by different utilities at different rebate levels.

Thank you very much for all your input. I really appreciate you taking the time to help me.

 

[Phog]

Yes, a gas water heater would require a vent. A power vented gas unit can use cheap plastic venting and could be side-vented through a wall, but the power vent blower is usually on top, and adds to the height- you probably don't have enough headroom.

When I looked into hybrid heat pump heaters 2-3 years ago, they were about the same height as the equivalent gas power vent.

I just looked up one of each (both Rheem 50 gal units) to see if I was remembering things wrong -- the hybrid heat pump unit was 3" taller than the gas power vent -- 61" vs 58".

Factoring in the 12" additional headroom required for the gas unit vs the 6" additional head room required for the hybrid heat pump unit, this leaves a grand total of 3" installed height difference with the heat pump unit coming out only very slightly ahead. This is typical of what I'd previously found. (But of course I will bow to the experience of a tradesman if it turns out this is not fairly representative of the two types).

Installing a gas line for a ~40,000 btu appliance can be very cheap or quite expensive, depending on how close the appliance is to the incoming gas / meter, and on whether there is an existing free connection such as a capped tee in the manifold.

If there is an open tee available on a suitably sized existing gas pipe, and a relatively short run to the new appliance, say in the 20-25ft range, this would be best case. The gas line install would be very cheap indeed. Plumbers in my area would run yellow flex line, and the install would be roughly $100 in parts + 1hr labor. ** not including the PVC exhaust

On the other hand, if the location for the water heater is all the way on the other side of the house from the gas service, and/or if the gas plumber has to cut in a new tee to tap into, installation costs can go up quick.

The main advantages to gas would be MUCH faster recovery time. The heat pump hybrid will recharge the hot water much slower, even with the resistive heater element on.

The cost benefit of the heat pump will also depend on the specifics of the install -- how much latent cooling is actually available for the heat pump to capture in the area where the water heater is located? If it is a small closed-in room with poor air flow, and this room is normally quite dry, this is a different situation than a damp, open, humid basement. The former situation would tend to negate the small annual cost savings that the heat pump gives compared to gas.

I'm not claiming that the gas power-vent is a better choice than the hybrid heat pump electric for this particular application. Just trying to help an informed decision to be made. To me the hybrid electric is not a no-brainer, and the cost of a gas install should be estimated & factored in. As well as the value to the homeowner of the added performance the gas unit provides.

 

[Dana]

The recovery time difference is real however I don't think that's an issue here, as the original description included:

"Small house, small demand. No kids."

If it were a family of 4 or more showering daily or filling large tubs it might lean the other direction.