Return Water Temp

Spring is finally close and I get to revamp my heating system. I want to connect, a still to be purchased, used or refurbed DF520 in series with my current oil burner.
I have a few questions about my new setup plans. From what I've read here the smartest way to do this is to connect the two boilers in series. I've seen some plans here that show a circulator between the two boilers. It makes sense to me because it will keep the water in both boilers approx. the same temp. What I can't figure out is what controls that circulator? Is it on all the time, on a timer, or is boiler temp used to turn it on/off?

I'm also looking at TACO's variable setpoint circulators. They speed up/slow down depending on the temp of the water being returned to the boiler. My thoughts about switching to this type of circulator is that it should help keep our bedroom temps even. Right now the first bedroom on the zone gets overly hot and the last one on the zone is cool. What temp should return water be? and are these ciruclators worth the extra money or am I just getting carried away with the 'latest and greatest'?

Hi Billw. The temperature differences between your bedrooms sounds like your zone is too long. The first bedroom is pulling too much of the available BTU's from the baseboard units,, leaving too little for the second bedroom..

You can close the air vent door/flap on the baseboards in the first bedroom, leaving more heat for the second bedroom. If you increase the circulation rate, you will get more heat to the second bedroom, but it will overheat the first bedroom even more..

Creating and installing a well balanced hot water zone takes some experience and skill...and sometimes luck. Sometimes a room at the end of a zone has more heat loss than calculated, resulting in a cool room.

Most baseboard units BTU ratings are based on 180* water.. so if the water is only at 150* by the time the water gets to the last bedroom, then the calculated length of the baseboard needs to be increased to make up for the lack of temperature differential.

Or if access is available, maybe making the last bedroom it's own zone?? Especially if it is the master bedroom??

A few questions.. is your current system a manifold with zone valves? or is it run with separate circulators for each zone?

As for hooking the boilers together, the 'best way' will depend a lot on the system you have, where you pull your domestic hot water, and if you are planing on using the EFM boiler year around for domestic hot water.

If you can show some photos of your current system, or draw a schematic of the current system? And give a description of your needs, expectations of the system..

Greg L.

Thanks Greg,

Here’s a better description of what I have now. It’s a peerless boiler with a DHW coil. I feed the output of the coil into a 55 gallon electric hot water heater. I used to shut down the boiler in the summers and heated water electrically. Allowing the boiler to cool caused leaks around the water heater coil and the threads on the boiler output pipe. I don’t shut the boiler down at all anymore and eliminated the leaking problem.

I have three zones 2nd floor has 4 bedrooms, a separate bath and a bath off the master bedroom. All of the radiators are copper finned. We’ve tried closing the vents in the first bedroom. The last bedroom on the loop still stays cooler. Now let me say this is really not that big of a concern. It’s not like one room is 80 and the other 60. You can feel the difference in temp but I never quantified the actual temperature difference. I saw those variable setpoint circulators and thought this might be an easy way to correct the imbalance.

The 1st floor zone has copper finned radiators and an additional under cabinet heat exchanger in the kitchen. The supply house that did the heat analysis for me told me to put it in because I didn’t have enough empty wall space for radiators. It’s worked well the last 15 years. Again I have the front room, approx 10 X 12 with the stairs to the second floor that is noticeably cooler than the others. Again not a major problem but something I would like to address when I do this changeover/upgrade. Each floor is approx 1,300 square feet. First floor has 9 foot ceilings, second floor has 8 footers.

I live on the side of a hill. The uphill portion of my basement is 6’ high, the lower portion of the basement is 10’ high which has two garage doors. I use this section as a workshop. I have a Modine heat exchanger set up in the garage. There is one circulator for each zone right now. When it’s real cold out and I work in the shop the furnace sometimes has a difficult time keeping up if all 3 zones call for heat. When that happens I just set the thermostat in the shop down until the other zones are satisfied.

Unfortunately I can’t fit the coal boiler where my oil boiler is now. There is no way to get coal in that area. I plan on sacrificing a section of my workshop to get both boilers, coal bin, and oil tank in the same place. Eventually I’ll put a hand fired unit where the oil burner sits now. I’ll use it as a backup if power fails and extra heat in the basement when it gets real cold. I can’t just let a perfectly good chimney sit idle.

I plan to continue using the DHW coil in the oil burner, mainly because I already have it. I plan on using coal to heat the water throughout the year. The oil burner is going to be strictly a backup in case we go away in the winter or have a problem with the coal unit. I want to add radiation in the basement and garage to keep the temp there around 60 when I’m not down there. I’ll put an electrical switch on the Modine for extra heat when I’m tinkering in the shop. When that thing kicks on it vibrates the whole house so I don’t want to rely on it daily. Eventually I’d like to add radiant heat in the kitchen and front rooms to keep the tile and hardwood warm.

We kicked around downsizing but we spent 12 years remodeling and building this place. Neither of us really wants to move. We're going to upgrade a few things over the next two years , the biggest being the heating system. Eventually, like next summer, I’d like to add radiant heat to the kitchen and front room just to keep the tile and hardwood floors warm. That’s why I’m trying to get the equipment sized right now. The DF520 has almost double the BTU output of my existing oil burner. So I think that unit is the smart choice for my needs.

I hope I gave you enough info. Thanks for the help

Bill W

Hi Bill,, Yes I think the EFM 520 would be the right size for your application... and since you plan on burning coal year round to heat DHW, you could continue to use the coil in the oil boiler, or get the EFM with a water coil..

You will need a circulator between the two boilers... or if you use a DHW coil in the EFM you could use manual isolation valves to shut off the oil boiler in the summer, You have lots of options..

Since you will be moving the existing boiler, and have to replumb a lot of it.. you can almost start from scratch with the design of the system,, use of the two boilers, or only one, etc.

About your circulator pumps.. what are they?? The common B&G red, motor/connector/oil bath/pump circulators.. The B&G 100 model? or are they the more modern cartridge circulators? in the zone where you have a cool room at the end of the zone,, a slightly larger pump would be a LOT less expensive than one of the automaticly variable ones.. There are several pumps with a manual three speed selector switch available from Grundfos.. the 15-58, and 26-96 I think I have those numbers correct, these pumps come as single and three speed models. With a three speed, you could manually pick a faster speed/higher volume for the zone and see if that fixes the cooler room.. You can buy these circulators on Ebay for a good price.. just get the retail and decide how much you want to pay.. I've bought the 26-96 single speed for $80 shipped off ebay,, they are a $250 pump..

Check out some of the threads about hooking boilers in series vs parallel vs primary/secodary.. PM forum member 'sting' and get the titles/publisher for the books he recommends on boiler plumbing,, or find them at your library.. and read up, You have an opportunity to plumb a really neat system..

Greg L
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The circulators I'm using are TACO 007. These were installed in 94. I haven't had a problem with them yet. I bought a spare when I installed them. It's still sitting in the unopened box. I already asked sting for the reading list. I'm looking forward to learning more before I pick up a tool. I've heard of series and parallel installations but not primary/secondary. I've got a month or so before I can start. Should give me plenty of time to figure all of this out. Thanks

Hi Bill, the taco 007 circulators are good units,, if I had known you were having some problems with the cool rooms,, I'd have loaned you a Grundfoss 26-96, I have a few spares [can't pass up a steal-of-a-deal on ebay] The Grundfoss 26-96 is a 1.70 amp pump, about twice the flow and twice the head pressure as a taco 007,, it would have been an interesting experiment to see if that would cure your cool-room. The Taco 007 is 0.74 amps I think... the Grundfoss 26-96 is roughly equivalent to a Taco 0011 pump..

I will suggest that you make your setup as easy as possible to load the coal bin or hopper that feeds the EFM,, with mechanisation if possible.. My coal hopper for my AA260 is only about 20' from my coal bin,,, but with my coal burn rate, loading the hopper each week with 14-1500# of coal does get old.. This year I'm thinking of figuring out an auger-feed system that I can load with my tractor's front loader..

Greg L

I'm putting the coal bin right in front of the garage door, 10 X 8 X6 should hold a two year supply of coal. The coal man should have an easy time delivering. The area has easy access, with no obstructions. The auger will be in the coal bin through a dog house. No shoveling, just rake the top of the pile flat, and empty the ashes.
It sounds like all I might need is a bigger pump, not the fancy variable speed pumps. I'll try buying one bigger pump over the summer. If that's the fix I'll replace the other circulator also. I'm looking forward to buying those books. Most of my questions are pretty basic and should be answered by reading a few manuals.