Proper indirect sizing?

psd_3

I am about to install a replacement oil fired boiler with indirect. I live in New Hampshire and my heat loss is estimated to be ~75,000 BTU. I have a private well, 2 showers, and 2 teenage daughters who like long showers :). I have decided to install a Buderus G115-34 boiler (104,000 BTU net) with outdoor reset control (using the Logamatic R2107). I am considering the HTP SuperStor Ultra-45 as the indirect and would use a 3/4" Taco mixing valve at the DHW output. The R2107 supports DHW priority control.

Questions:

Is the SSU-45 large enough to handle the cold start recovery of the boiler?

I was considering a Taco 0010 circulator pump for the indirect, but my contractor thinks it's way overkill and recommended the 008 instead (seems reasonable given the pump curves and required flow rates vs pressure drop). Any other opinions?

The choice of the G115-34 is slightly larger than needed for my heat loss, but thought it would help with balancing heating needs and DHW recovery, particularly in mid NH winter months. Is this a reasonable decision, or should I size the boiler based on purely heat loss, which could put me in the G115-28 instead? I have been told that the R2107 will help accomodate the larger boiler without issue.

Thanks for the help

hr

Ain't never had

to much hot water

If the girls shower right after one another, or other DHW loads, you mmight consider upsizing to a 60 or 75 indirect. Probably stay with the smaller sized boiler and furnish more of a dump load of DHW.

For DHW loads that happen in a short period of time I prefer the larger tank capacity.

This would help keep the boiler closer to the correct heating load size, also.

Generally a 75 gallon gas fired light commercial water heater has a 75,000 btu/hr burner. For comparison.

hot rod

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kevin coppinger_4

I agree w/ HR....

I have never had anyone complain about having too much hot water or too much closet space...Another thing to consider in the equation is the fact you have a well. Here in New Hampshire the well water can be very cold thus taking the tank water temp. down fast. I have a SSU60 gallon w/ a Buderus 115-21 and it works well enough w/ 3kids. You can always prioritize and still do the mixer(make sure its a good one sparco,taco5000)... no watts 70A 's I'd do the 28 series unlees you plan on doing a large addition to your home soon...hope this helps...kpc

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Roger Litman

Indirect sizing

The two teenage daughters, if they take long showers and the flow rate is high will need a larger storage tank than the usual 40 or 45 gallon one which is correct for most households without a large bathtub or multiple showers running at the same time. You may want to make sure that the piping from the indirect is 3/4 " so that there is enough flow to satisfy the usage. Of course the more water heated for these showers will not come for free. I try not to use a mixing valve at first, but if you need more water- then you can add one of the good ones mentioned. The closer you match the firing rate of the boiler to the house, the better off you are with longer cycles and only on those rare design days will the hot water usage affect the system. Depending on where you are in N.H., you should be using a -5 to -20 as your design day condition.

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Ken_15

What is the recovery time with the small boiler, extended tank combo? Or do you even care about the recovery time due to the increased volume on standby? With a mixing valve isn't the 60gal extended to close to 85 or 90gal? What happens to your heating capacity when the small btu boiler is trying to make hot 60gal of water?

I have always gone with more btu's to match the heat load and hw use. I know some say that the indirect doesn't go into the btu equation for design purposes, but you also need to be able to heat the water and the house at the same time once in a while.

kevin coppinger_4

I have had...

the system up fired a bit. I have not had a problem w/ recovery( only about 10 min) and the system is using a tekmar 260. If the heat load is that close to the max load of the boiler I might consider going to the next size up. he did have 10k to play with and that was on design day.(Load was 75k, boiler IBR net was 85k.) jm2c... kpc

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psd_3

Indirect Sizing

Thanks for all the help ... tomorrow is decision day!

I live in Southern NH and design day accounted for -10F

The decision to not provide some extra head-room is always a tough one as you can't always predict future needs. It's a much easier decision to bump up to a 60gal indirect cause it's just a bit more $$ now. It's harder to convince myself not to build in some boiler head-room cause that surely would be expensive to fix later.

Other than not be optimized for "best" efficiency, what are the other down sides? Can some of these, like perhaps shorter cycles be worked around with the Logamatic R2107 control? The folks at Buderus indicated that the R2107 will allow me to compensate for a "slightly" larger boiler without issue, but I'm not sure I understand the hows and whys.

Cliff Brady

Consider waste heat reclamation and

a smaller 40-45 gallon indirect. My family of five does fine on a 40 gallon indirect. I put in an S4-60 waste heat reclaimer in the stack and recover probably 50-60% of waste water heat from the bathrooms and kitchen. Now is the time to do it especially if when you are piping in a new water heater and mixing valve. The preheated water feeds into the water heater and the cold side of the mixing valve so basically less water is going through the heater which may extend its life. I have 130 degree water right out of the indirect going to the laundry and dishwasher and mixed down 115 degree water going to the rest of the house. Recovery is fine even with 155 degree supply water to indirect.

Save money with a smaller indirect and have lower energy bills.

Their website:
http://gfxtechnology.com/

sootmonkey

Hello

This is how I was taught to size tanks. You have to know your "pond" size. Your "pond" is the amount of uninterupted hot water that you need. (Ex. You have a bath tub that holds 50 gals., your pond size is 50 gals.) You said that you have two teenagers who like long showers. If you figure that both showers may be running at the same time, your load could be 5 to 6 gallon per minute. 5 gallons per minute, times 20 minutes, equals a 100 gallon "pond" size. The tank that you will need will be 80 percent of your "pond." In this case an eighty gallon tank would be needed. If you have 3/4" fittings on the tank, pipe it in 3/4" copper. If they are 1" fittings, use 1" copper. I'm not a big fan of mixing valves on indirects. I welcome other ideas.

Tom Giedraitis

I have to agree on upsizing the stored water.
Recently was talked out of a combo of larger tank and smaller boiler, and I'm not happy with the result.
We aren't taking showers like teenagers yet, but it takes 20 minutes to get a full tub, because the hot water runs out about 2/3 of the way up and the wife needs to wait to finish filling it.

We previously had an electric 60 gal which did the job, the 45 gal SS even turned up to 140 is not cutting it.
Wish I had gone with the 60 or even 80 (80 has much bigger heat exch coil)

Good luck, and go with your gut.

Robert O'Connor_7

indirect

I did my own house 3yrs. ago. I had a used WM 30 gal. indirect (i bought it for a job & the customer wanted a bigger one after I installed it, but never used it) It's working great for me & the three women in my life. It's set @ 145 deegrees with a mixing valve @ 120 for domestic uses and the 145 water going to my clothes washer. The indirect tappings are 1" (I reduced them to 3/4") I have no priority relay. The system recovers in 8 mins in the summer & 12 in the winter. Now at first I was going the 75 gallon route. Good thing I didn't, I have just enough hot water, and when I don't, waiting 8 - 12 mins (which is still less than the time it takes the girls from drying off and fussing around in there) is not too bad when you think I saved the initial cost about $600 difference between the two, and the fuel costs annually. Hey maybe i sold myself the SNAKE OIL..? boc

Ken_15

Sounds like your boiler is too small to keep up with the hw needs. It takes alot of btu's to heat the water in order to keep up with the flow rate. I am not sure but I believe it is 50,000 per gallon/ min. So if your flow is 3gpm it sounds like 150,000 btu's would be needed to stay even.

DaveGateway

indirect

According to what I'm reading in the Burnham book it shows the AL40a tank -Max. first hour rating gal/hr @ 140 deg.142 gal. 115 deg /197 gal . continuous rating gal/min @140 deg 2.26 - 115 deg/3.38 . boiler output needed 133,000 {based on 200 deg boiler temp , 50 deg water inlet temp @ fully recovered tank }

DaveGateway

correction

AL40a max first hour rating gal/hr @ 140deg=175gal, 115deg =242 gal

hr

The only exact answer

would be to calculate, or project your actual DHW needs, incoming water temperature, etc. Then hold the girls to that calc. Install a 15 minute timer on their shower valves

Seriously, having installed hundreds of indirects, storage beats recovery and smaller sized tanks every time. I have a 36 gallon Triangle Tube in my own home. it will ot fill the tub when my wife "soaks"

But it does recover quickly after my son showers in the AM allowing an additional shower in 12 minutes or so.
I added 100 gallons of solar preheat before the 36 indirect, which helps a ton. Even without solar gain it warms and preheats by being in the mechanical room.

In summer months I turn the LP boiler off completely and get all my DHW from several solar panels.


So your trade off is dump capacity and longer recovery. Or small showers with 15 minute intervals with a smaller indirect. YOU need to decide now which fits your lifestyle best

hot rod

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heatpup

Sir I am a novice. I installed a ssu-60 with a munchkin 140M... I have 4 children all of which take long showers in 2 bathrooms all within 30 minutes of each other in the morning. I have not yet run out of hot water. I did when I had two 50 gallon 48000 Btu hot water heaters running. So far any how...by the way, i have my water temp set at 125 and a mixer set at 117. I will not ever have a home without an indirect again.

Ken_15

We haven't istalled a system w/out indirect in years!!! It is the only way to go w/ oil fired equipment.

psd

Now that's funny ... but I ain't laughing

"Then hold the girls to that calc.
Install a 15 minute timer on their shower valves "

Yep, with a "large" coin operated switch and one free pass a day. At 45 minutes I'm ready to shut the water supply off in the basement. My first step at getting things under control was to not allow boom boxes in the bathrooms. My wife doesn't understand why it's an issue. I guess I'm just out numbered. Perhaps I'm going about this indirect in the wrong way, maybe much smaller is better ... a built-in sort of time control .

psd

Taco SR503 and SR504 Schematics

Anyone know where I can get detailed schematics for the Taco SR503 and SR504 zone control switches. I'd like something with the detail that's typically given by Honeywell (like for their R8888A). It appears that something changed in the definition of H, N, P ZC between the SR503 and SR504 timeframe, but the literature on Taco's website is not very clear.

I'm slaving a number of manufacturers controls together and really need to understand where each terminal goes in the Taco circuit ... i.e, which terminals feed the 24v transformer, which terminals bring in supply voltage for the zone circulators, etc. Some controls can't source much current and I don't want to find out that it's supplying source current for multiple circulators through the next control. Is there a "standard" definition for these terminals that all manufacturers follow?

kevin coppinger_4

I have one of te taco books....

really nice...I could fax you something...kpc

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Steve_39

storage v.s. recovery

Reading this thread has brought back sooooo many discussions with my wife over the years. My family has an uncanny ability to power through hot water. We've had a 60 gal. electric, oil boiler with coil (I was only renting!), 40 gal. gas, 50 gal. gas, 50 gal. gas with 80 gal. solar backup.....All of them were defeated by my family. This lead to the "I'm married to a plumber and can't get decent hot water" discussion over and over. Last year I finally convinced my wife that we were going to buck up big and put a good system in. We settled on a 140 Munchkin and a 70 gallon Vaughn indirect. After 2-weeks and no complaints, I got daring and installed a 127 jet sunflower shower head in the bathroom my teenager uses then removed the flow restrictor and dared him to run it out of hot water. 45 minutes later he dragged his pruned up body out of the bathroom and said "WOW, that's a great shower"

Nuff said~! I'll go with storage in a residential setting every time.

Steve Eayrs

PSD, have you considered...................

stacking the Buderus 115-34 (or 28) on top of the Buderus LT-160 or LT-200???? We do that a lot. The LT-200 is about 60 gallons, has decent recovery, and makes a great package with the boiler. I prefer the burner up off the floor, (because of dirt, etc.) and if in a garage install it takes care of the 18" min. off the floor, code requirement.
Is there something I don't know about these tanks that I should?? I didn't see anyone else mention them on this thread. I have installed maybe 150 of them in the last 10-12 years, w/ zero problems.


Also when you mentioned "cold start" of the boiler, were you talking about the actual boiler being cold start, or the water in the in-direct tank?? These boilers have a fair amount of mass and even though you would have a hard time hurting them w/ an occasional cold start, the time lagg involved in cold starting them makes it a little hard to produce very much dhw that way. I would recommend setting the min. boiler temp. at 140 or so, and you should be able to make a lot of dhw.

Steve

psd

I have looked at both the Buderus LT160 and ST200, but for the money I think that the HTP SSU-45/60 are a better deal. I personally don't like stacking the boiler on top of the indirect because it makes maintenance more difficult. The boiler and indirect will both go up on blocks for my installation.

As for cold start ... during the heating season the outdoor reset control (R2107) would maintain operation at some elevated temperature, but not necessarily a temperature appropriate for DHW production. Given DHW priority, the time lag would not be as great as a true cold start. However during the warm weather, the control would allow starting from ambient and the boiler would require a longer recovery period before DHW production could occur.