Built in Domestic Hot Water Coil?

So I am still figuring out different ways to plumb this thing when my addition gets completed and was thinking I needed to clean or replace the side arm heat exchanger on my hot water heater then it hit me.....Duh, my boiler has a built in domestic hot water coil! So my question is does this thing really work well? By the numbers I think it's 6gpm so as long as I flow less than that I will have infinite hot water, assuming the boiler stays at temp? How hot will the hot water get? If this works it would be so nice to get rid of that 70 gallon hot water heater (was a gas but valve quit working so I just kept it hooked up for winter since it's hooked to side arm exchanger, I run a 40 gallon electric in the summer).
For those that have theirs hooked up, how do they work?

They tend to work very well! Everyone has there own thought. Indirect water heaters work very well also.

My coil in my New Yorker gets city water fed in, and then it goes to my inlet of my electric tank, so my electric never comes on because it's fed with 160-190 degree water whenever I use any hot water, I have a mixing valve on the hot side going to my house. I want to put a pump in though to circulate the water through my coil instead of feeding cold water to it, because in the winter when there's calls for heat, 50 degree cold water going to the coil really puts a hurting on it..

What's your plan as far as summer goes? Would you like to burn all year round? Or just in the winter?

I'd be shocked if you can get a sustained 6 GPM of hot water out of a DHW coil.

6 GPM x 60 min./Hr. x 8.34 lbs./gal x 55 degrees of temperature rise = 165,132 BTUH

220,000 boiler input BTUH x 0.75 (efficiency factor, being gracious here) = 165,000 boiler output BTUH
(Which requires the burning of about 18 lbs. of coal per hour)

That leaves zero BTUH for home heating.

3 GPM sustained is more realistic, albeit at a demand of ~82,600 BTUH. (Which requires the burning of about 9 lbs. of coal per hour)

They work just fine. Simple to test it.

Leave your current setup hooked up. Pipe to the coil in the boiler with isolation valves. Shift to the coil in the boiler. If it don't work, go back to the heat exchanger. All it cost you is two valves and some piping.

Larry's calculations are spot on as always. However, your house is not going to have zero BTU's going to it because the water use is not 100% 24/7. You will experience a drop in boiler water temp but your no newbe to that right? It will recover and it won't be pulling any more BTU's than you have currently been using.

Realistically, what single family home would ever draw even close to a sustained 6 gpm load...certainly not the one that would get by on a 40 gallon electric model.

Rev. Larry, I fully agree that coils can work well, but the OP made mention of infinite DHW! Temporary DHW demand is much different from infinite (sustained) DHW demand. I have a coil, and it has worked well for 5 years. And my boiler has only about 60% of the BTUH capacity of his boiler. But I don't tax it up to my coils rated 3 GPM for very long. Our shower heads are 2 GPM. Only one person can use DHW at a time in our house. But then, there are only the wife and myself.

Most people don't realize it, but often DHW is more taxing on on a boiler than is home heating.

swyman wrote:So I am still figuring out different ways to plumb this thing when my addition gets completed and was thinking I needed to clean or replace the side arm heat exchanger on my hot water heater then it hit me.....Duh, my boiler has a built in domestic hot water coil! So my question is does this thing really work well? By the numbers I think it's 6gpm so as long as I flow less than that I will have infinite hot water, assuming the boiler stays at temp? How hot will the hot water get? If this works it would be so nice to get rid of that 70 gallon hot water heater (was a gas but valve quit working so I just kept it hooked up for winter since it's hooked to side arm exchanger, I run a 40 gallon electric in the summer).
For those that have theirs hooked up, how do they work?

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Hello Swyman,

The DHW coil in my Kaa-4-1 works very well. The 30 gallon propane water heater did not run much at all during the winter months.

I will suggest that you install an Watts Series 70A tempering valve on the outlet side of the coil to prevent scalding as I had done with mine -its in the National Plumbing Code too.

Don't make the same mistake I did and not have a second set of unions sweated in to allow a clear installation/linear path for the coil loop as they are very long and you have to be careful not to ding the copper coil.

About the picture you uploaded- is this where you are beginning the construction for the basement BILCO door?

There may be more than one option for where to locate the Watts thermostatic mixing valve.

We used a DHW coil in an EFM 900 and it was awesome. In your case, I agree you're not going to get 6 gpm out of it in real time. The actual number depends on the inlet water temp and the rise needed. Using typical values you probably could get a max of 4.0-4.5 gpm; more than a modern showerhead and less than many older ones. You also start with the BTU's in 42 gallons of hot boiler water; between that inventory and the real-time capability it seems like a good producer for most normal DHW needs.

To prevent the heating load from giving you a cold shower (and stressing the boiler), my limited understanding of controls would be that it is important that the heating circulator shuts off when the boiler temp goes below the low limit setting. To ensure satisfactory DHW under those circumstances, you might need to adjust the low limit. For us 160 was a good setting but "your results may vary".

Agree that a tempering valve of some type is essential.

Mike

hotblast1357 wrote:They tend to work very well! Everyone has there own thought. Indirect water heaters work very well also.

My coil in my New Yorker gets city water fed in, and then it goes to my inlet of my electric tank, so my electric never comes on because it's fed with 160-190 degree water whenever I use any hot water, I have a mixing valve on the hot side going to my house. I want to put a pump in though to circulate the water through my coil instead of feeding cold water to it, because in the winter when there's calls for heat, 50 degree cold water going to the coil really puts a hurting on it..

What's your plan as far as summer goes? Would you like to burn all year round? Or just in the winter?

I have always shut down when the weather warms up and will probably continue to do so. Though winters here can be very cold, my family really looks forward to me starting up the boiler as they love hot showers! I have always ran without a anti-scald valve and never had an issue and can come in handy when cleaning things! That's a good idea of running through your coil first before the water heater, then I would never have to mess with shutting valves off to bypass or switching over if a fire ever went out.

lsayre wrote:I'd be shocked if you can get a sustained 6 GPM of hot water out of a DHW coil.

6 GPM x 60 min./Hr. x 8.34 lbs./gal x 55 degrees of temperature rise = 165,132 BTUH

220,000 boiler input BTUH x 0.75 (efficiency factor, being gracious here) = 165,000 boiler output BTUH
(Which requires the burning of about 18 lbs. of coal per hour)

That leaves zero BTUH for home heating.

3 GPM sustained is more realistic, albeit at a demand of ~82,600 BTUH. (Which requires the burning of about 9 lbs. of coal per hour)

The 6gpm is what they advertise, I have not checked it but my shower head and all faucets on the house probably wouldn't be more than 3gpm??? This is something I will have to do a test on!

Rob R. wrote:Mineral buildup is a concern with tankless coils. If you have hard water, it should be softened if you intend to use the coil.

I have basically a water treatment plant in my basement. I had hard water with natural gas, iron, salt.....you name it. I have a Kinetico system that starts with a 180 gallon holding tank that aerates as it's filling that gets liquid chlorine injected to kill the iron bacteria. The top is covered and vented outside to get rid of the natural gas. So there's a pump in the tank that goes to a charcoal filter to remove the chlorine, then on to the softener, then through the house. There is a RO system for the kitchen and fridge. When I first moved in you could take a match and hold it under the faucet and would throw flames as it spit and sputtered. Also found a old video I took of my daughter (age 1) taking a bath and the water was orange......nasty! I spent some money but we have perfect water since!

lsayre wrote:Rev. Larry, I fully agree that coils can work well, but the OP made mention of infinite DHW! Temporary DHW demand is much different from infinite (sustained) DHW demand. I have a coil, and it has worked well for 5 years. And my boiler has only about 60% of the BTUH capacity of his boiler. But I don't tax it up to my coils rated 3 GPM for very long. Our shower heads are 2 GPM. Only one person can use DHW at a time in our house. But then, there are only the wife and myself.

Most people don't realize it, but often DHW is more taxing on on a boiler than is home heating.

I guess I should pick my words more carefully, just standard use hot water. Gets hit heavy at night when 4 kids take showers (well some nights they all shower!) but that's about it and again the showerhead is probably 2gpm so shouldn't be to taxing on the system?

lzaharis wrote:
About the picture you uploaded- is this where you are beginning the construction for the basement BILCO door?

Yes, the BILCO door will be just about where the dumpster is located in the pic......as of right now. We have the rest of that porch gone and are going to do a final layout so that door location may change when we see how everything is going to look.