monoflo issues in one zone

**ctreefer** · 09-11-2012, 02:24 PM

Hi all,
It's my first time posting here and hoping I can get some guidance before I start asking local professionals.

I bought a home in CT 3 years ago and am disappointed with the heating in one zone. The last set of baseboard takes till the end of the boiler’s cycle to get warmed up on one side of the house.
It’s a hot water boiler hydroponic system with baseboard (fins). There are 4 zones (1 indirect hot water) (3 living areas)
Boiler is Burnham Oil fired. Main loop in basement starts with 1.5” black pipe into expansion tank down center of basement then splitting off to the multiple loop and mono flo zones. There are some check valves in this area but don’t recall the placement. The primary loops (front ½ of house and back ½ of house have their own loops at the split that return to the boiler) supplying the monoflos is 1” black pipe coming off the 1.5” with multiple mf and regular T’s coming off for each baseboard. The return going into the boiler passes through the circulator pump which is flowing towards the boiler.
The main living area on the main floor (split level ranch) is a mono flo system. The other two are loops for the bedrooms and downstairs.

I think they screwed things up when they designed this system because its my understanding you don’t want a long line of radiators on a monoflo system and that last line near the end of the main loop is over 60 of baseboard before it drops back down. (this is the line that is forever cool near the end till the end of the boiler cycle (15 minutes or so).

There’s part of me that just wants to scrap the whole monoflo system and go with a loop but not sure if it’s a wise decision because one side of the loop (series) is almost double the length of baseboard as the other side.

I just feel like this is a very inefficient use of heat. The basement is always toasty because of all the heat running through that main loop but the main floor is slow to warm up at the far ends. I’ve bled all the lines till the valves were dripping so I know its not an issue of an airlock. I’ve also checked all the direction of the monoflos to make sure they were installed correctly and they all seem to be right.

Coming from my old house which was much simpler (1 zone series loop) it always warmed up much quicker and the slantfin was always hot to the touch. This system it seems the heaters just never get that hot.
Technician during last cleaning changed (increased nozzle size) some nozzles sizes on the injectors thinking this would help for some reason but the only thing it seems to have done is use more fuel (maybe in my head but last year was warmest on record and we used same gallons as previous year.)

I’ll try and draw up a diagram of the plumbing tonight and post it tomorrow as I’m sure the description above is somewhat confusing.

To add fuel to the fire, I’m debating on converting to gas from oil soon so will be replacing 25 year old boiler and hot water system. Want to make sure I’m not just wasting $$ on new equipment that runs through a possibly poorly designed heating system.

Any help would be greatly appreciated. Even if it’s just guidance on what to look for in choosing a professional.

Thanks

**johnjh2o1** · 09-11-2012, 03:21 PM

You are correct you can not expect a monoflo tee to supply a loop of baseboard. What should be done is to put the loop on it's own zone.

John

**Dana** · 09-12-2012, 09:05 AM

Just be aware that when breaking out a 60' chunk of low-mass fin-tube baseboard into it's own zone it's micro-zone, prone to short-cycling the boiler. Even with the smallest oil boilers out there running 180F AWT that zone can only emit only about half the boiler's burner output, and at lower temps (or bigger burners) it's even less. If it's cast iron rather than fin-tube it has at least some amount of thermal mass, but whether it's enough depends on the thermal mass in the boiler, the burner size, and the amount of hysteresis in the boiler controls.

This is also an issue when you swap out the boiler for a gas-fired unit, either modulating-condensing or cast-iron. A mod-con running under outdoor reset control for more condensing efficiency can short-cycle itself into an early grave with low-mass microzones. Whether mod-con or cast iron it's important to pick the very smallest unit that actually meets the design condition load unless you add thermal mass to the system.

Since you have a history of fuel use on the oil boiler, it's possible to work backward from fuel use and the boiler's steady-state DOE combustion efficiency to put a firm upper bound on the whole house heat load at the 99% outside design temperature. If your oil supplier stamps a "K-factor" on the billing, the K-factor on a mid or late winter bill has all the information we need other than your outside design temp. If you are too far from any of the CT locations in the ACCA Manual-J list (linked to above), it's pretty easy to estimate an outside design temp with a zip code using Weatherspark.com's historical data.

If your toasty basement is currently uninsulated, the heat loss out the basement could easily account for 25-30% of your total fuel use, so don't be afraid to undershoot a boiler sizing number derived from a fuel-use analysis. (And if it's mostly unfinished, even with condensing-gas it's cost effective to insulate the basement. Check other threads here on how that's best done without creating mold problems, or start a new thread under "remodeling" or something.) In many cases it's cheaper to insulate the basement than to rip up an existing hydronic heating system and start over. If the basement still overheats you can insulate the pipes too, but the better bang/buck on fuel use is to start by insulating the foundation walls along with insulating/sealing the foundation sills & band joists first.

**ctreefer** · 09-12-2012, 10:37 AM

thanks for the info. Hadn't thought about insulating the walls. The basement is prone to water issues which I am still tackling. (long story and getting longer but there is hope still.) Anyway, the walls are cinderblock and I've painted them with the water proofing. I'll search out the links for insulating them so again thanks.

Question though, if I insulate the basement and it's already warm won't it just get warmer? I understand that I'm getting heat loss through the walls but how does that affect the upstairs if the basement is sealed off other than warming the floorboards?

First time posting a pic here but hopefully it works. That's the layout for my current setup. You can see that long 60'+ section which is slantfin. Not sure if that whole system can be converted to a loop in series.

**Dana** · 09-12-2012, 01:45 PM

If you insulate the basement and seal/insulate the band joists the heating system will run less often- it may be somewhat warmer or somewhat cooler, but you'll be burning a LOT less fuel. Warmer floors on the first floor lower the amount of heat that needs to be delivered by the radiators & baseboards, so it's something of a balancing act.

When I sealed & insulated the basement walls to ~R18 in my Worcester, MA house the average mid-winter temp in the basement bumped up from ~65F to ~68F, but the shoulder-seasons the basement dropped a bit under 65F due to the lower duty cycle of the heating system. Previously it would be warmer than 65F in the mid-fall or mid-spring seasons, cooler mid-winter due to the higher heat loss, a fraction of which was air leakage at the band-joist/foundation sill & elsewhere. Now the biggest heat loss out of the basement is through the slab to the ground, but that's WAY below what the wall + leakage loss had been. YMMV, but for most 1 or 1.5 story houses in this region foundation wall losses & leakage are more than 15% of the heat loss, and if your basement is running in the mid-70s during the heating season it would be almost surely be more than 20%, probably more than 25% of the total heat loss/fuel-use.

Deal with the bulk water issues first, but there are good/better/best ways of dealing with wall insulation, all involving at least some amount of foam (rigid &/or sprayed.) Exterior sloping & drainage are job-1, and it may take a buried skirt of roofing-membrane attached to the foundation sloping away to redirect surface water sufficiently far away from the foundation:

Sometimes it's necessary to jackhammer out an interior perimeter drain sloping to a sump to bail. If the basement has a history of flooding it doesn't mean you can't insulate, but it does affect your options.

Converting to a series loop may end up with even worse balance problems than you have now, and should only be done after a thorough analysis by a competent hydronic designer. (I'm pretty good at hackin' with the napkin-math on hydronic systems, but I'd probably hire this one out rather than guestimating and hacking it into balance.) If it's just the fin-tube zone that's out of balance, treating that and that alone is probably do-able. If it's possible to cut in a ball valve on the parallel section of the main loop between tees to/from the fin tube you could force more flow in the fin-tube, at the expense of lower flow elsewhere. It may work fine that way, but that's strictly in the nature of a hack, not a well-designed solution.

Cutting the fin-tube free and capping the Tees, and putting the fin-tube on it's own circulator as a micro-zone would surely work from a heating point of view. You'd need to deal with the short-cycle aspects, but that's a tractable design problem.

Part of the reason the baseboard section stays cool until the end is that while radiators put out heat in proportion to their temp- even when they're only 90F and rising it's radiating, whereas fin-tube falls off pretty sharply below 110F or so since nearly all of the heat transfer is via convection, which requires bigger delta-T between room & water temp. North of 120F it's pretty similar to other types of heat emitters in terms of linearly increasing output with temperature. If it were cast-iron baseboard it would do better, but that's not to say it would still be well balanced with the rest of the zone. (Replacing it with brand new cast-iron baseboard would run at least a couple of grand, but probably less than a grand if you went with reclaimed goods. But that's still not likely to be enough on it's own.)