Not using DHW coil in steam boiler.

SeanL

Hello everyone, I have a oil burner steam boiler that is single pipe system.  It’s on the older side but with oil prices being what they are i wanted to install an electric hot water heater.  I currently have hot water through a coil in the boiler that I believe is separate from the steam heating system.  Can I cut and cap the hot and cold lines going into the coil, keep the feed to the boiler attached and then add the electric hot water heater somewhere else in the room?  I’m not sure if the DHW coil in the boiler effects the steam portion is anyway.  Thank you in advance!

Sean

random12345

Another possibility is to keep the coil and its piping and add a bypass to the electric WH. Depending on oil and electric rates, you could then use one or the other as you see fit. Or use a heat pump WH instead. Might be cheaper. The steam will work whether you use the coil or not. I feel your pain on heating oil prices...

mattmia2

You have to leave the coil open if you disconnect it since it is still being heated by the boiler.

Jamie Hall

The water in the coil doesn't connect to the water on the steam side --no to worry. But, as @mattmia2 says, you have to leave the coil open on at least one side.

The other trick is there is probably an aquastat on the boiler to keep it warm to heat the hot water. You won't want that any more, so find it and disable it.

SeanL

Thanks everyone. Yea I figured I would leave the old water lines open so pressure can’t build up.  As for the aqua stat I can pull that out of the burner control no problem.  I don’t have any experience will steam so didn’t want to screw anything up.  What is the steam side aqua stat?  Is it the based on pressure rather then temperature?   Thanks again for all the help.  

EBEBRATT-Ed

an aquastat is installed in the steam boiler to keep the boiler hot enough to supply domestic hot water. It is installed below the normal water line and senses boiler water temp. Usually wired in parallel with your heating thermostat it should be disconnected when the tankless coil is not used.

The 'steam side aquastat" you refer to sense's boiler steam pressure. It is a safety control, a high limit pressure control and shuts the burner off if the steam pressure gets too high. Make sure to never disable this.

AdmiralYoda

Here is another thought. Run the coil in the boiler to the new water heater. Use an Aquastat to keep the output temperature something reasonable, like 120-140F or so.

If the boiler is in operation due to the steam heat being on, it will fill the water heater with hot water and the hot water heater won't have much work to do. If the boiler is off and cold the water heater will work as it normally would without the boiler in the loop. You get free hot water and storage during the heating season.

I'm no expert and have never done this but it almost sounds like a good idea.

random12345

AdmiralYoda said:

Here is another thought. Run the coil in the boiler to the new water heater. Use an Aquastat to keep the output temperature something reasonable, like 120-140F or so.

If the boiler is in operation due to the steam heat being on, it will fill the water heater with hot water and the hot water heater won't have much work to do. If the boiler is off and cold the water heater will work as it normally would without the boiler in the loop. You get free hot water and storage during the heating season.

I'm no expert and have never done this but it almost sounds like a good idea.

I have considered this as well, but heard it could lead to increased condensation on the boiler's heat exchanger plates in the off-heat season. The cold water running through the coil is constantly pulling heat from the boiler till it gets below the dew point, and the humidity in the basement air condenses > filth + rust, which then has to be cleaned up. Not sure if it's true. Just putting it out there. I think a bypass would need to be installed to prevent this from happening. Here's where I first heard about this. There are also a few others on the Wall.

https://greenbuildingadvisor.com/question/domestic-hot-water-from-steam-boiler

JakeCK

random12345 said:

Here is another thought. Run the coil in the boiler to the new water heater. Use an Aquastat to keep the output temperature something reasonable, like 120-140F or so. If the boiler is in operation due to the steam heat being on, it will fill the water heater with hot water and the hot water heater won't have much work to do. If the boiler is off and cold the water heater will work as it normally would without the boiler in the loop. You get free hot water and storage during the heating season. I'm no expert and have never done this but it almost sounds like a good idea.

I have considered this as well, but heard it could lead to increased condensation on the boiler's heat exchanger plates in the off-heat season. The cold water running through the coil is constantly pulling heat from the boiler till it gets below the dew point, and the humidity in the basement air condenses > filth + rust, which then has to be cleaned up. Not sure if it's true. Just putting it out there. I think a bypass would need to be installed to prevent this from happening. Here's where I first heard about this. There are also a few others on the Wall. https://greenbuildingadvisor.com/question/domestic-hot-water-from-steam-boiler

Pipe in a bypass to prevent the cold water from passing through the boiler in the summer months. 

Personally I would buy a hpwh and use that during the summer months and switch over to the boiler when you fire it up at the beginning of the season. 

Mind you there is no such thing as a free lunch. The heat is coming from somewhere in the winter, and that somewhere is the boiler or the electric elements. My guess would be that it is marginally more efficient to use the boiler in the heating season vs using a hpwh that steals the heat from the space and thus the boiler. One less energy conversion happening. And then use the hpwh in the summer to help cool and dehumidify the in the summer. It will make a difference.

I replaced my 15yr old gas water heater with a hpwh and shaved off entire winter month worth of gas usage over the course of a year and did not increase my annual electric usage at all because of the offset from the dehumidifier and lower load on the ac.

pedmec

I think a heat pump water heater with a steam heating system is a great idea because all that steam heat being lost in the basement is recovered and used by the hp water heater. I have tried to convince my commercial customers who use district heating to use hp water heaters but they are scared of the recovery or lack there of. During lunch and dinner times the restaurants get extremely busy and can't afford no hot water. Nobody wants to play guinea pig.

We use to install them in au bon pans 30 years ago. I didn't stay long enough to find out how they worked out. Wish I knew.

JakeCK

pedmec said:

I think a heat pump water heater with a steam heating system is a great idea because all that steam heat being lost in the basement is recovered and used by the hp water heater. I have tried to convince my commercial customers who use district heating to use hp water heaters but they are scared of the recovery or lack there of. During lunch and dinner times the restaurants get extremely busy and can't afford no hot water. Nobody wants to play guinea pig. We use to install them in au bon pans 30 years ago. I didn't stay long enough to find out how they worked out. Wish I knew.

That's a good point about the latent heat being recovered by the HP... However the laws of conservation still dictate that you are not going to get ahead. Insulating the basement walls would be more cost effective. 

ethicalpaul

You will get ahead because the HP water heater has about 4x the efficiency of any other source.

ChrisJ

JakeCK said:

pedmec said:

I think a heat pump water heater with a steam heating system is a great idea because all that steam heat being lost in the basement is recovered and used by the hp water heater. I have tried to convince my commercial customers who use district heating to use hp water heaters but they are scared of the recovery or lack there of. During lunch and dinner times the restaurants get extremely busy and can't afford no hot water. Nobody wants to play guinea pig.

We use to install them in au bon pans 30 years ago. I didn't stay long enough to find out how they worked out. Wish I knew.

That's a good point about the latent heat being recovered by the HP... However the laws of conservation still dictate that you are not going to get ahead. Insulating the basement walls would be more cost effective. 

ethicalpaul said:

You will get ahead because the HP water heater has about 4x the efficiency of any other source.

Of course the irony here is the heat pump can only transfer heat from location to the other.
In this case, it's transferring heat from your boiler to your hot water. The boiler is loosing heat to it's surrounding area, which you're cooling off with the heat pump so it's increasing the boiler's losses.

Like @JakeCK said, no such thing as a free lunch.
And I highly doubt using the heat pump to heat the water using heat generated by the oil fired steam boiler is more efficient than just using the boiler directly.

ethicalpaul

Well you’d be wrong in this case. It is amazingly cheap to run and results in zero noticeable ambient temperature difference. The heating needs for the water (via heat pump) are so tiny compared to heating a home in the winter.

don't make me post my energy graph for this thing again 😂

ethicalpaul

To clarify, it’s not transferring heat from the boiler. The boiler already lost that heat to the leaky basement with cold walls. The heat pump grabs that heat before it is lost. Free.

the coil however does steal heat directly from the boiler

ChrisJ

ethicalpaul said:

To clarify, it’s not transferring heat from the boiler. The boiler already lost that heat to the leaky basement with cold walls. The heat pump grabs that heat before it is lost. Free.

the coil however does steal heat directly from the boiler

If the basement is above ambient (the temperature of the dirt), it's being heated by something.

My basement hovers around 55-60F all winter.

ethicalpaul

Yes and that’s happening regardless of what kind of water heater you have.

The difference is mine uses that heat whereas yours tries to heat your yard

JakeCK

ethicalpaul said:

Yes and that’s happening regardless of what kind of water heater you have.

The difference is mine uses that heat whereas yours tries to heat your yard

I must disagree. Is the floor joists between your basement and first floor insulated? If not it is with in the building envelope of the house and thus heated and conditioned space, even if unintentionally. Stealing the heat from the basement will steal it from the upstairs where most of that heat will end up eventually for the same reason you lose most of your heat through the ceiling and into the attic of your house. 

Again the heat is coming from somewhere, and there is loss everytime energy is converted. The laws of conservation demand it. No way around that.

That leaves you with two choices, you either purposely bring the basement into the envelope by insulating the foundation($$$$) and slab if possible($$$$$), the first and best option. This option means the hpwh is the slightly less efficient option in the middle of the winter, but overall as a system the most efficient. Add in a bypass to directly heat the water with the boiler dhw coil from say end of October to April or May will get around that and in a way you get to eat your cake and have it too. 

Or you move the boundary of the envelope to the bottom of the floor joists and make the basement unconditioned. The worst option for the same reason HVAC equipment in unconditioned attics are a bad idea. This second option has higher risks of moisture, mold, and damage to equipment in addition to the standby losses to the outside. However in this case a hpwh will not be stealing the heat from the house and will be the most efficient option. But overall less efficient than option one because of boiler losses to the outside.

Now if one wants to be super efficient let's talk about a2w heat pumps and a hpwh and suddenly the calculus changes, a lot. 

You also have drain waste water heat recovery. They can recovered up to 50% of the heat in water going down the drain. But... With using a hpwh the benefits of that get marginalized. 

ethicalpaul

I’m still wrong if the temperature in my basement is the same regardless of if the heater is on?

the waste heat is heating up the space but there is much greater heat loss to the walls and windows and drafts that my water heater is stealing. That is the important distinction

ChrisJ

ethicalpaul said:

I’m still wrong if the temperature in my basement is the same regardless of if the heater is on?

the waste heat is heating up the space but there is much greater heat loss to the walls and windows and drafts that my water heater is stealing. That is the important distinction

If Paul talks and no one is there to hear it, is he still wrong?

JakeCK

ethicalpaul said:

I’m still wrong if the temperature in my basement is the same regardless of if the heater is on?

the waste heat is heating up the space but there is much greater heat loss to the walls and windows and drafts that my water heater is stealing. That is the important distinction

Tbh yes. Energy is energy, it can neither be created nor destroyed. Or allow me to be more precise mass-energy can neither be created nor destroyed. That law is such that even blackholes can't even escape it. It eventually leads to their heat death and evaporation. 

I'm not sure what you mean when you say its the same even when the heat is not on? If we're talking not running as in the non-heating season then obviously it is being warmed by the great outdoors just like the rest of the structure is. And the hpwh is the best option. 

If you mean between cycles that is because of the heat loss from both the system and from the house it's self. Energy can and does flow both ways.

If it is cooler outside of the thermal envelop of the house, energy is flowing out and we need to add energy to keep it warm inside. The rate of heat loss to the outside is dependant on the temperature difference, air leakage, and thermal resistance of the walls. We all know and understand this. The presence of a hpwh is not going to change this beyond lowering that delta T by cooling the inside ever so slightly. It isn't going to some how magically steal the heat back from the outside(unless it cooled the inside to a temperature lower than outside of course), or steal it before it has a chance to escape. The temperature upstairs will just cool ever so slightly as well. Now you might not, actually probably will not notice such a small change but that is what is happening. 

I'd be willing to bet that two otherwise identical homes except one has a boiler and hpwh and one has just a boiler with dhw coil that during the heating season their energy consumption will be identical. And to account for daily temperature fluctuations only taking measurements when the outside temperature remains cold enough to require heat.

JakeCK

Now that I'm fully awake, I want to be clear I am not knocking hpwh's in the least. I have one, I love it. It works amazing and I was able to reduce my gas consumption over the course of a year by the average for the month of January without increasing my overall electric usage. I just do not want anyone having any misconceptions about what they are and how they work.

I also wanted to run some numbers to further illustrate my point. My hpwh pulls about 600 or so watts while it is running on heat pump only. This is backed up by the energy usage it is reporting and my own logs for run time. It ran for about 4 hours and used 2.58kwh today. Divide that out and that is 645watts an hour. Now assuming its getting a COP of about 3, that works out to about 1935watts an hour. Now I have a 115k btuh output boiler, do you want to take a guess at how much longer my boiler has to run an hour to make up the heat the hpwh steals?
.
.
.
A little over 3 minutes. Or about 12 extra minutes a day. 

To the OP, either option of installing hpwh and totally discontinuing use of the dhw coil, or piping it for use just during the heating season are both viable means to an end and the difference in energy consumption between the two of them is marginal. 

I would not however replace with just a regular old electric hot water heater. Unless you have cheap electric rates that will most likely cost you more money.

ethicalpaul

I'm aware of the conservation of energy. This is not about that. I'll try this one more time and then I'm out. It won't be the first time people have disagreed with me

There is a big tanker truck of water in a desert. Its valve is open so that it is emptying water into the desert. There is a short stream of water along the ground and then the water seeps into the desert sand.

I am standing there with a cup and I am dipping it into the stream and pouring it into my canteen.

Am I taking water out of the tanker?

The tanker is the boiler generating heat in my basement. The stream is the *temporary* and *fleeting* heat in my basement. The sand is the cold walls and windows of my basement. My heat pump water heater is the canteen.

ChrisJ

@ethicalpaul most people use a lot more hot water than you.

For several reasons, but I'm mainly thinking of one.

JakeCK

Yes you are taking water out of the tanker. If that stream of water is what is necessary to maintain the houses temperature, removing it from the stream however little is removed is now heat that is not available to keep the house warm.

Where you are in error is the assumption your basement is not part of the thermal envelop of the the rest of the house. It is, even if unintentionally. If it isn't then let's open up all of the windows down there and if you have one, the cellar door too and leave them open all winter long, then we can talk about how it is outside that thermal envelop. The only way it is not considered part of the rest of the house is if you have it sealed as well as your exterior walls. Which means some type of air barrier on the bottom of the joists, insulation, a basement door that remains closed all winter long, and all other communication paths between down there and upstairs sealed off.