Gas conversion questions.

Paul_H

<span style="font-size:12pt">Hi everyone, I’ve got a similar situation as in a previous post about Boiler Sizing. I’m contemplating a change from oil to gas and had some questions regarding boiler / dhw options. First some particulars:</span>

<span style="font-size:12pt">I have a small ranch house appx 1300 sq/ft; heated with hot water baseboard. This is divided into three small zones; one of which is an extension that was made our living room. The other two zones are the rest of the public space and a separate zone for the three bedrooms and a half bath. I will finish a portion of the basement in the future adding approx 600 sq/ft of heated space and another zone.</span>

<span style="font-size:12pt">I did a heat loss/gain calculation about 8 years ago when adding central air; the loss for the first floor was approx 28,000 btu/hr at design temp (Long Island, NY - JFK). Adding the basement brings the total up to approx 40,000 btu/hr. (This may have improved slightly by replacing some windows a few years ago.)</span>

<span style="font-size:12pt">I’d like to go with a modulating/condensing boiler to take advantage of all the tax credits and rebates through National Grid; however all the units listed in their program seem to be too large.</span>

<span style="font-size:12pt">I’d also like to install an indirect DHW tank, but in researching boilers I’ve read that they must be sized correctly to prevent short cycling, and it seems that with that low output requirement for heat would not be enough to use an indirect for DHW. </span>

<span style="font-size:12pt">What are my options here? Is it worth going high effciiency here with a tankless? Or am I better off going with an atmospheric boiler with outdoor reset to help raise efficiency and using the indirect tank? Is there anything I’m missing?</span>

<span style="font-size:12pt">Thanks,</span>

<span style="font-size:12pt">Paul</span>

Henry

MId-efficiency is ideal

With such low heat loss, it does not pay to do the mod-con install!

Here are two 66,000 BTU Raypak Residential with built-in pump and bypass, electronic ignition and vent damper. We replaced two 140,000 BTU cast iron oil fired with these small efficient units. We have been installing them since they came out (15 years?). In all that time, we had only one failure, a defective gas valve!

For hot water, a Rheem Pro40-40 or similar will provide you with adequate hot water at a reasonable cost. A proper chimney liner is required for this type of install.



Regards,

Henry

CMadatMe

Henry Henry Henry

I have to disagree here. He could certainly use a mod/con, grab the tax credit and rebates those alone bring the boiler down to the price of an atmospheric. He has plenty of choices of mod/cons that will save him fuel and provide perfect comfort.



He first needs to get a new heat loss done. Break that heat loss into the zones and then take the total footage of the board that is existing in each zone and find himself a nice baseboard chart to see what water temp he would need at design conditions to overcome his heatloss by zone. Most homes are 35 percent over radiated. Without this it is really a guessing game as to which is the best course of action to take.

I'm willing to bet a boiler like a Vitodens 100 WB1B-26 or similar mod/con would be fine in this application with a 40 gal indirect. It's just a matter of running the math.

Charlie from wmass

The mod cons can work well

The great thing about the mod cons is they adjust to the heat load and can ramp up for the domestic load. a small indirect can be used or plate heat exchangers if water quality is good.

Paul_H

What to do ... What to do?

Thanks for the replies. I am leaning toward the modcon route for a couple of  reasons. My current boiler is a Burnham V74 with a 5gal DHW coil; however it is only (?) 16 years old. I am having a problem with the DWH coil and began looking into indirect tanks when I found out about the rebate and tax credit on new equipment. To justify the added expense (even with the credits) i need to feel that it will be paid back in better efficiency over the next few years; I don't know that a traditional boiler setup will do that.

I'm having trouble settling on a DWH option though. If money was no object I would have a tankless heater installed and abandon the chimney altogether, but I don't know if the added expense is worth it versus a traditional hot water heater. To install a traditional heater I would have to line the chimney, another added expense.

The best option would probably be the indirect, however I don't know if I can run one with a boiler that fits my heating needs, and I don't want to give up efficiency by installing a larger boiler to satisfy the indirect.

I had been looking at the Lochinvar Knight wbn050, i think it may be the best fit for my situation, but I don't think it will provide enough output for an indirect. Am I missing anything here?

Thanks again!

CMadatMe

Yes You Are Missing Something

Like I said in my previous post. Get a heat loss done. Don't worry about the outputs at this point. You really need to run the math in order to get a sense of what is going on here. Break the heat loss out into your zones and rooms. Then compare the losses to the footage of board at given water temps from a baseboard chart and find a heating curve. That label on the side that states "95" is a smoke screen for any mod/con. That number is dependent on low water temps and if you don't run the math you cannot make a educated decision. The added btu that you may have in the mod/con that may not be needed for the heating benifits the recovery or how efficicently you can make hot water.



Look at your project in the long term. Maybe you can start pullling out the residential board and change is out to hi-cap board as you can afford it. Why? The ability to run lower water temps thus increasing your efficiency. Example. 1 foot of res board at a 1gpm (10,000 btu) flow rate puts out 550 btus with 180 degree water. Hi-Cap board utlitizes 160 degree water to do the same. That alone almost gives you a 7% saviings based on the known that for every 3 degree you can run a system with water temps below 180 you save 1 percent of fuel.



Too many homeowners and contractors get caught up on that label number. To be truthful system efficiency plays just as or even more important part of the whole equation.  There are so many options you can added today or down the road when you can afford them that will help the payback.



We spend alot of brain power deciding on new equipment to replace the old but we spend zero time replacing an on a old system to a new. Just take the circulator. Doesn anyone not think that a circulator such as a Grundfoss Alpha or simliar pump does not provide better system efficiency than a traditional 007 or similar pump? This is a product that doesn't have to be done toady but could be simply added tomorrow with very little labor.

Paul_H

Thanks Chris

I did see your previous post. I do intend to do a new heat loss although I don't think that it has changed dramatically since the 2002 calculation. I installed Andersen double hungs where there were double pane replacements before. I will improve somewhat in the basement where I installed 4 double pane windows in place of single panes.

 

Reading your post made me take a closer look at my baseboard though. It seems that I have the whole Slant-fin range in my house in different rooms along with a kickspace heater and one old cabinet convector in the half bath. (Plus some pipe reductions that I will need to rectify)



 When calculating the output for the baseboard should I assume 1gpm or 4gpm.(or do I need to calculate that as well?)



Thanks for your time Chris, I appreciate it!

Paul

CMadatMe

Flow Rate

Your flow rates for your zones are dependent on the heat loss for each zone. If zone 1 has a heat loss of 25,000 btu's your flow rate would be 2.5gpm. If zone 2's heat loss is 15,000 you would have a flow rate of 1.5gpm. Baseboard outputs per foot would be different for each zone. That's where the chart comes in. Also, if you have a kickspace heater and do go with a mod/con you have to change the aquastat on it. There is an optional low temp aquastat avail for all current kick space heaters and you do need to change it.



I attached a study that was done concerning condensing with a baseboard application. Hope this helps in your education process

Paul_H

Now I'm confused.

I'm just learning this so please be patient if I use some terms incorrectly.

Isn't  flow rate determined by the pump and the restriction through the piping (head loss?).



I like to research things and understand as much as possible so I can make an informed decision when it comes time to hire the job out. Thanks for your help.



Also, thanks for the BNL study, I've read some other reports by them but never saw this one.



Paul

CMadatMe

Flow Rate/Head Loss

Flow rate is determined using the following formula



8.33 (weight of 1lb water) x 60 (coverts to minutes) x delta-t (temp diff between supply and return) divided by btu = gpm



8.33 x 60 x 20 = 10,000 divided by 100,000 = 10gpm. Total system flowrate. If I have 4 zones i would then plug in the numers for each zone to get it's individual flow rate.



For residential systems we have been using the following "rule of thumb" for many years to calculate the required pump head:

1. Measure the longest run in feet

2. Add 50% to that

3. Multiply that by 0.04, and

4. That's the pump head

Example:

1. 100 feet of total piping (to radiation and back)

2. 100 feet x 1.5 = 150 feet

3. 150 feet x 0.04 = 6 feet

4. Pump head requirement = 6 feet



So you would need a pump that could delivery 10GPM at 6ft of head.



Hope this helps

jp_2

both are right

you can calculate/estimate the expected flow rate, but the pump will decide the flow rate based on the flow resistance it "see's".  within its ability to pump.

CMadatMe

I'll agree with that

Most systems are running a 8 to 10 degree delta-t because that little green flat curve pump is on every boiler. This is why we should all be using Grundfoss Alphas or similar pumps. The ability to adapt to changes in the system as zones open or close when zoning with zone valves. I think the day of zoning pumps with today's technology is just about over.

As designers and installers we are all doing our customers an injustice by not offering these types of options in our systems. At times we tend to forget we adapt new high tech boilers into old systems but never seem to update the systems just heating plants. I think there is a huge market for system updating. Think of all the jobs that have been installed in the last 5 years alone. How many customers could you go back to tht are looking for fuel savings without dumping alot of money. The addition of heat managers, pumps such as the Alpha, hydro seperators on those pri/sec jobs. There is such an oppotunity out there but it really doesn't seem that too many are jumping on it. Just my opinion.

Paul_H

Beginning to see the light.

I'm still having some trouble with the heat loss/flow rate/head loss stuff, but I do get what you're saying about system efficiency. If I understand the BNL study and what you are saying about switching to commercial baseboard correctly, if I can lower the water temp required to 160 degrees, then the boiler could be condensing  all the way down to design temp. System efficiency impacts boiler efficiency. I never thought of it that way. Thanks!

Now I have to find time to run all the numbers.



I'm wondering about a couple of new things now. As I said before my house is an extended ranch with a basement. I split the main zone into two zones, seperating the bedrooms from the Kitchen, D/R and Bath.

My L/R is the extension and is a seperate zone.



Looking at the old Heat Loss calc the L/R loses 8320 btu/hr; the Bedrooms = 8909; Kit & D/R & Bath & Halls = 9927.

The zones are fairly equal, but could they be too small to achieve a 20 degree delta T?



Should I consider restoring the bedrooms to the main zone?

Even though the L/R is an extension, if I have an accurate Heat Loss calc, should I consider adding this to the main zone and have just one zone for the main floor?

 

Opinions?

CMadatMe

Zoning

Since the heat losses are similar you could make them one zone but there are other things to consider. Where would the therm be? Does solar gain influence setpoint on the therm? If not, does it influence another room served on the same zone? How about the kitchen. Does you wife like to cook? Does that play any part in influencing setpoint? Do you like to entertain? The added heat loss from us also plays a part.



I'm glad to see you are beginning to understand how the system plays its role in the big picture.



Concerning your question on delta-t. Most hydronic systems while designed for a 20 degree delta-t never seem to achieve the 20. Your most likely to see a 10 or even less due to that little green flat curve pump that comes on every boiler. That's why I would suggest zoning with zone valves and change the circ out to a Grundfoss Alpha or similiar delta-p pump. It will help with the flow rates in the aspect that the pump has the ability to adapt to opening and closing zones. This will help you in a deeper delta-t.



These all can be done as you can afford them. Dependent on your budget, you could install the mod/con today and add these items as as long as you prepare for them prior to the intial install.



 Changing out the baseboard per zone from residential to hi-cap overtime can provide you with many years of added fuel savings and comfort. Save small percentages over years verus taking it all on the front end. In the long run you may end up with a bigger savings percentage.

Tim McElwain

Paul, you can also add

Outdoor reset to your system and increase the lengths of baseboard so that lower temperatures are possible to allow low return temps (below 130 °F) this will allow condensing if you are going to use a Mod/Con boiler.

Nathan_6

WBN50 with 80 galoln squire

Paul,



If it makes you feel any better I have a wbn-50 with a 80 gallon squire that has been installed in a two apartment bed-n-breakfast here in Alaska for the last 2 years and there has never been a complaint about lack of hot water.  The upstairs apartment has a shower and a deep soaking tub. 

As for the small zones of the bed room keep them separate for comfort reasons. You can always ramp delay a Knight boiler if you like to keep it firing at the Lower fire rate for longer period of time to increase the overall system efficiency.  To properly set up the ramp delay you need a detailed zone by zone heatloss at design temp and average temp so that you can set the curve and the ramp delay

I've installed many Kinghts and Viessmann boilers they are both excellent choices.  Trust me once you have an indirect you won't want to go down the gas water heater road ever again.  In my own home I cut my gas bill in half by just replacing the old gas water heater with an indirect. I cut it again 2 years ago by replacing the boiler with a mod-Con.

Paul_H

Maybe I misunderstand something.

Thanks for the info Nathan, however I am a bit confused again and I'm thinking that I'm not understanding the tank ratings. I looked up the 80 gal. Squire, and it calls for a Min coil load of 171,000 btu/hr; much more than the wbn50 can produce. Am I reading too much into the ratings?, does making DHW the priority zone make a difference in the ratings?

Thanks,

Paul

Paul_H

Thanks Tim,

Just from looking at my old heat loss calc and breaking down the zones/rooms it appears that I am over-radiated anywhere between 1.5 to 2x, so I should be able to lower water temps right from the start. I do have some higher output B/board (Multi-Pak 80) installed in my L/R and this is my most over-radiated room. I will look to balance the rest of the rooms to this in the future.

Nathan_6

Number is alittle miss leading

Paul the chart your reading is a little miss leading as the 171,000 btu/hr is the minimum btu's you need to get the results they show on that chart.  If you open up the squire manual and look on page 21 you will see the first hour rating of the 80 gallon squire coupled with a WBN50 boiler at two different flow rates.

As for priority it won't affect the the charts ratings as they are figured with all of the boilers output which priority gives.  If you were to install an indirect on a system and not have it on priority you bet it would affect your DHW output as you would now be sharing your boilers btu's with the heating circuits as well as the indirect tank. 



Hope this helped Paul

Paul_H

Thanks Nathan

I'm putting too much emphasis on the numbers. I see that stand alone DHW heaters don't approach these numbers either. 

bob eck

gas conversion

check out triangle tube prestige solo or prestige excellence depending on btu heat loss also you can use their smart 30 to 120 gallon stainless steel indirect water heater for domestic hot water. great boilers and water heaters

I went from a 30 plus year old weil mclain oil boiler with domestic coil to a triangle tube PE110 boiler with built in water heater and last year I saved $1050 using nat gas vs what I would have used in the old oil boiler. Sure I would have saved some money with a new oil boiler and a indirect water heater but not that much. this years prebuy for oil in my area is $2.80 so this year gas vs oil I will save $1400

Paul_H

Love the idea..

of the Prestige Excellence, I think it would take care of all my needs. However I think it is still oversized on the heating end for me. THANKS FOR THE INFO!

bob eck

boiler

look at triangle tube prestige solo PS60 60,000 btu input can use their smart 40 stainless steel indirect water heater or install a tankless gas water heater like a noritz or install a A O Smith vertex 50 gallon gas water heater that has a 76,000 btu input and delivers 127 gph first hour and 92 gph @ 90 temp rise. you can also install Alsons 1.6 gpm shower heads that will reduce the amount of hot water used and save you money on heating of your domestic hot water. 1.6 alsons shower head works great you do not even know that you went from a 2.5 gpm shower head to a 1.6 gpm shower head also using less water when showering you will lower your water and sewer bill if on a city system or if you have your own private water system and septic system you will be using less water and these systems will last longer.

Paul_H

Thanks!

I called National Grid yesterday and arranged for an estimate from one of their contractors. I wil probably look to get three or four more before I make a decision.

Thanks to everyone for all the information you've given me, I truly appreciate it. Any of you from Long Island?

I'm sure I'll have more questions after I start getting estimates.