Indirect Water Heater or Not

tomklein11

I am considering either a standard efficiency or high-efficiency Weil McLain boiler install. I want to replace my current gas water heater at the same time with an indirect water heater.

I've scoured the net for advice; however, I find the insights from some incredibly savvy individuals tantamount to much of the other stuff I read.

My questions:

1. Am I making the right choice to pursue indirect?
2. Is it equally an ok decision whether I go with a high-efficiency gas boiler or a standard cast iron?
3. What type of servicing is required on an indirect? Ie. What yearly maintenance is required?
4. What tank size would be sufficient for a long shower or two long showers simultaneously?

Lastly, and perhaps the most ignorant question, what mechanism allows for just the indirect tank to be heated versus the rest of my house in July.

Any advice on switching to indirect when installing a new boiler is appreciated!

Many, many thanks

(2400 square feet, gas, baseboard heat)

nicholas bonham-carter

Use the SlantFin app, or another to calculate your heatloss, so the new boiler can be properly sized, and not too large. The app will also enable you to determine whether you have enough baseboard radiation to benefit from a high efficiency mod on boiler.
There is a lot to be said for both cast iron, and modcon, even though one may offer a feature missing in the other.
An indirect will give you plenty of hot water, if also sized correctly. It will be on a separate zone, not controlled by the thermostat.
Choice of the installer is most important, and you are very wise to be doing this research before diving in, and this site is the best source of information available.
What sort of boiler have you got now?—NBC

STEVEusaPA

tomklein11 said:

...Lastly, and perhaps the most ignorant question, what mechanism allows for just the indirect tank to be heated versus the rest of my house in July.

Properly piped, and properly controlled, the boiler will fire to charge the tank when needed, and/or heat the zones when called.
Outdoor Reset (ODR) is part of another strategy that will only allow the indirect to call when the outside is above the ODR set point.

Wellness

Indirects are hard to beat for efficiency in the winter time when you are running the boiler. But in the summer, your boiler and indirect will be adding to your A/C load. The best compromise is to get an indirect with an electric heating element, so you can shut off the boiler during cooling season. But those are really expensive.

nicholas bonham-carter

If you were comparing the BTU’s needed to heat 50 gallons of water in either a stand alone water heater or an indirect, then I would say the indirect would use the BTU’s more efficiently, and therefore place less of a load on the A/C.—NBC

Wellness

I'm not sure the BTU needed to heat DHW to a specific temperature is the variable that needs to be examined. Wouldn't it be the heat generated inside the living area when gas combustion is taking place? What's more, the excess heat with an indirect would be coming from two different places: a boiler and indirect, not to mention the boiler flue and that piping that's connecting the two appliances. Are you saying that doesn't matter?

Big Ed_4

As far as boilers ... High efficiency condensing boilers reach those high efficient numbers running at low temperatures 120*-150*. Since your home uses baseboard for radiation 180*-200* it will not be a good match. Radiant and radiators I would recommend one.. Condensing boilers are higher maintenance normally and higher yet running them on the higher temperatures . I always recommend home owners with them to buy a spare parts kit . One would need to stock for the supply houses today don't .


If you're not upgrading the radiation I would recommend a simple cast iron boiler properly sized boiler using the heat loss calculation . Adding a true out door reset control. This will max the efficiency for the heating system using a 80%+ boiler.

Hot water will be the highest load, larger then the heat ... From what you so far mentioned , two shower at once , you already doubled what you need ... You will need to calculate the load , flow rate of hot water drawn , incoming and out going water temperature .. You can measure the flow rate with a stop watch and 5 gallon bucket . Normally the showerhead with resistor should be 1,5 GPM if you only take a 10 min shower you will need 15 gallons of water . The extreme rainforest set up I seen was near 15 GPM you would need 225GPM for a 10 min shower... One 10min 1.5GPM and the second 1.5GPM with 30min you would need 60 gallon tank on standby .

Indirect or stand alone hot water heater . If we know the boiler size and the hot water needed . Recovery may be faster with the indirect , depends on BTU's of the boiler and boiler supply pipe to indirect . The BTU input of the stand alone HWH .ball park 50kBTU will heat up 1GPM 50*.. Is the chimney big enough to handle two units ...Heat Loss calculation ! .If you can get away with just storage then either or ...

STEVEusaPA

Wellness said:

I'm not sure the BTU needed to heat DHW to a specific temperature is the variable that needs to be examined. Wouldn't it be the heat generated inside the living area when gas combustion is taking place? What's more, the excess heat with an indirect would be coming from two different places: a boiler and indirect, not to mention the boiler flue and that piping that's connecting the two appliances. Are you saying that doesn't matter?

I don't think it makes hardly any difference at all. I wouldn't even factor into a usual residential situation.
My boiler runs maybe 3, 10 minute cycles (at most) to recharge my 60 gallon indirect during the day in the summer.

bob eck

Do a heat loss on the house. Check and see how many feet of baseboard element in the house. If the house has more baseboard that needed you might then be able to use a high efficiency condensing gas boiler with lower water temps. You could use a combi boiler and dump the hot domestic water into a electric water heater. During the heating season use the combi boiler to make your domestic hot water and then in the non heating season just let the electric water heater make your hot water.
A cast iron gas boiler with a indirect water heater is a good option. Weil McLain has a cast iron gas boiler 90% AFUE that vents sidewall with PVC pipe plus there are other brand cast iron gas boiler that vent sidewall with stainless steel vent pipe.
Find a good heating professional and they can walk you through the process of different type of boiler and together you can pick out what will work the best for you.

lchmb

my opinion...Weil Mclain GV90..get the best of both worlds...not all the bells and whistles of a mod/con but a lot less of the headaches as well.. Get the boiler sized to the heat loss, run the indirect on priority..dont add btu in for it.. installer is the MOST important part.. if done right you'll be real happy...

mikeg2015

Standby losses on a 10 gallon boiler with a flue damper will be similar I’d suspect to a atmospheric water heater standby losses up the stack. But boiler firing efficiency will be 3-5% higher. BTU output is much, much higher.

Just like tankless water heater, high effeciency boilers need significant electricity for the inducers. Some dismiss this, but 100 watts any time it’s firing plus post purge is significant and you lose some here there too on post purge.


One thing to consider is that the newer gas water heaters our company is finding are disposable. In particular if the spark arrestor screens get plugged with dust, some are not possible ot clean, so you have ot pitch the whole heater and put a new one in.