Adding an Indirect water heater

dineshj

Hi. Currently, I have an undersized (by 10K btus) hot water boiler. I was going to get a bigger sizer gas boiler (+25K btus) but I can't add any more btus to my current chimney liner. I need to replace my conventional 36K btus gas hot water heater anyways so I was thinking of adding an indirect water heater.
The new boiler would be around 85% efficient.
Are indirect water heater worth it in northern NJ? I use the boiler for six months in winter and it is idle for the other six months. Would adding an indirect be inefficient because of summer time use or just as efficient?
Will my boiler life expectancy decrease because of running year round?
Thank you for any help.

mattmia2

The indirect should be more efficient than the tank type water heater, can produce more hot water if sized properly, and if you choose stainless models compatible with your water chemistry can last a lot longer. They are better than direct fired water heaters but also more expensive.

A heat pump electric water heater is also an option.

Hot_water_fan

Currently, I have an undersized (by 10K btus) hot water boiler.

How do you know this? That's very uncommon.

dineshj

Because it takes about two hours to heat up the home by 10 degrees. So a bigger boiler and air sealing the crawlspace will help to bring the load down.

Hot_water_fan

That doesn’t mean it’s undersized. It could be the radiation is too small or not functioning correctly or the setback is too big. Not worth replacing a boiler over. I’d bet if anything, the existing boiler is too big. Undersized typically means the boiler would run 24/7 on the coldest day (and if undersized by 10k btu, probably the coldest 10-20% of days) and the indoor temp would decrease. Yours isn’t doing that. If you doubled the size, you’d  still have an hour wait on that setback if the boiler is the constraint. If the radiation is the constraint, you might have the same two hour wait. 

You’re correct on the insulation though.

EBEBRATT-Ed

@dineshj

Since your in NJ if I were you I would contact @clammy or @EzzyT and have them look at your system. Very unsual for a boiler to be undersized

Zman

dineshj said:

Because it takes about two hours to heat up the home by 10 degrees. So a bigger boiler and air sealing the crawlspace will help to bring the load down.

Why would you want to increase your temp 10 degrees in under 2 hours? My house would take at least 12 hours.
I am guessing that you are being limited by your emitters rather than the boiler.
Upsizing your boiler will almost certainly waste more energy. Think Highway driving vs City.
What size boiler do you have? How big is your house? What area do you live in?

Nest thermostats coincidently make great hockey pucks

dineshj

Hi. I live in northern NJ. The boiler is 75k btus. I have a 1,000 sqft first floor. The basement is where the boiler is and is unheated and has exposed pipes. The second floor is a separate unit and they have their own heating system. First floor has uninsulated walls (maybe R-5 with plaster and lath and drywall and aluminum siding) and 11 windows that are rated R-2. 

Below is a picture of the pipes. Maybe the pipes are too big and has lot of water to heat. That’s why it takes so long to heat up?

Is the boiler properly sized? Thanks for any help. 

Hot_water_fan

That boiler is gigantic for the space. Way oversized. Why do you use a 10 degree setback? 

Zman

I am sure you are being limited by your radiators and not your boiler. If you really want to waste energy with "city driving" just get a programmable or wifi t-stat and turn the temp up sooner.

dineshj

It’s 75k input and 62k output. It takes about 3 hours in the morning when it’s 20 degrees out to go from 64 degrees to 74 degrees indoors. We usually turn the heater off at night or leave it at set temp so we can sleep in the colder temps. Otherwise the heater would cycle on and off all night and condensate. 

I don’t think I would want to turn the heater on at night or leave it at higher than 64.

pecmsg

If the heater is cycling then its too large compared to the size of the emitters. You don't want to go larger!

Hot_water_fan

I wouldn’t worry about condensation. It will always cycle because I suspect your heat loss is about 20,000 btu. Nothing really to do about that. How about you set it to 68 degrees at night or learn to live with the recovery time? It’ll save you a new boiler. 

In terms of the indirect, it’s a coin flip. No real advantage or disadvantage to one. It’ll have more capacity and last longer, but I doubt you need more capacity. Lasting longer is fine if you stay in the house, if you move you lose that investment. It’ll be more efficient in the winter and less so in the summer compared to a conventional tank. They also make high efficiency tanks that’ll be more efficient. 

EBEBRATT-Ed

@dineshj

The last thing you need is a larger boiler. Contact one of the heating guys I mentioned in my previous post and get your system brought up to snuff. You won't regret it

Zman

If your boiler is short cycling, that is a sign that it is oversized. You should be able to add an indirect with no issues.
How old is your existing boiler? What model? Is it working well?
It might be worth upgrading the controls to reduce short cycling and then just putting it on a schedule so the AM warm up time is not an issue.
If you must have faster warm-up times, you will need more radiators, not a bigger boiler.

dineshj

@Zman @Hot_water_fan @pecmsg
I have a 2017 Laars boiler. 
I meant that it cycles at night when the indoor temperature reaches 64 and the heater kicks in and turns on and off at that point to maintain 64. 

When in the in morning I set it to 74, it will constantly run for three hours and not cycle on and off.  Below are the cast iron radiators photos.

dineshj

We had a oldie160k output boiler that we replaced. It used to heat the whole two floors. And it would take about an hour to heat just the first floor on a 30 degrees outdoor temp with 10 degrees setback. 

Hot_water_fan

When in the in morning I set it to 74, it will constantly run for three hours and not cycle on and off. 

But it will cycle at 74 once it reaches temperature. Due to the size of the boiler, cycling is inevitable.

Just don’t worry about the recovery time if you want the house at 64 at night, it’s not related to the boiler size. Your boiler is at least 2x too big, possibly 3x, but it’s not worth replacing. Maybe just open the bedroom window at night and leave the thermostat at 74?

Zman

If you have the newer controller, you can adjust the outdoor reset (if the sensor is installed), and change the boiler on/off differential. Which model do you have? What is the operating temp of the boiler? What are the average cycle length when it is short cyclng?

JakeCK

Maybe install trv's in the bedrooms you want cooler and then use a smaller setback for the rest of the house.

mattmia2

It is probably running much lower supply water temp than the old boiler. I'm not sure what model you have, but some have settings to gradually boost the supply water temp if the heat call lasts a long time to increase the output of the system. Just changing the beginning of recovery from setback also works as others have mentioned. I have a 20 year old thermostat that remembers the recovery rate for the past few days and starts recovery before the set time so it will be at setpoint at the set time.

dineshj

Zman said:

If you have the newer controller, you can adjust the outdoor reset (if the sensor is installed), and change the boiler on/off differential. Which model do you have? What is the operating temp of the boiler? What are the average cycle length when it is short cyclng?

@Zman I have the Laars JVS. Currently, the setting on the boiler is that once the water temperature reaches 170 and the indoor temp is satisfied, the boiler starts to cycle. If the indoor temp on thermostat drops by half a degree, the boiler turns back on, which usually happens after about an hour. 

Zman

Short cycling is generally defined as more than 6 cycles per hour.
If your boiler is cycling less often than that, that's just normal operation.
If you turn the boiler temp up, it will probably get the room up to temp faster.
If you increase the on-off differential the boiler cycles will get longer.

Jersey2

I think you have the right sized boiler, but what is the limitation of the chimney liner such that can't add any more btus to it? Is it too small a diameter, or is it made out of a material that can't handle the extra heat?

dineshj

Jersey2 said:

I think you have the right sized boiler, but what is the limitation of the chimney liner such that can't add any more btus to it? Is it too small a diameter, or is it made out of a material that can't handle the extra heat?

@Jersey2

The current corrugated liner is inside a brick lined chimney. The current liner is tightly jammed in the chimney. It would take a lot of manpower and drilling the bricks out to get the liner out and install a new smooth wall liner.

dineshj

lkstdl

JakeCK's suggestion for TRVs in the bedrooms combined with a simple programmable thermostat that comes out of setback an hour or two early would likely solve your issues.

Are you running at a constant 170F water temperature or using outdoor reset?

Some boilers have a "boost function" which temporarily raises the water temperature if setpoint is not reached with a user-defined period of time.  Higher water temperature allows faster recovery. I'm not familiar with the JVS but I know some of the other Laars boilers support this.