Sizing hot water duct coil

Old 11-22-10, 09:09 PM
Thread Starter
Join Date: Oct 2004
Location: Mount Airy, MD. USA
Posts: 31
Received 0 Votes on 0 Posts
Sizing hot water duct coil


I am messing around with some ideas for 'free' heat.. one of them is by using an abundance of wood that I have, burning that to heat water and installing radiant heat panels to gather radiant heat during the day; dumping into a large reservoir (about 2000 gallons).

What I am trying to find out is how to size the 'hot water duct coil' and the flow control valve.. this looks like a radiator that you place inside the ducting on the supply side of the air handler for those of you that are not familiar.

Things I know... I have the J load calculations:

1383 Sq feet total conditioned space for zone1
Heating Loss BTUH 34218
Latent Gain BTUH 4214
Sensible Gain BTUH 22899
Cooling Gain BTUH 27114
Cooling Tons 2.26
Cooling CFM 861

Things I don't know:

How to size the air handler accordingly.. for example I have looked at the Ruud uhsl-hm2417ja technical data sheet and it specifies minimum heat/cool cfm 720, nominal heat/cool cfm 800 and maximum heat/cool cfm 900. Does my J load number of 861 mean that this unit is within spec?

I am assuming that the cfm from the j load is how many cfm's are required in the entire conditioned space.. if I place a hot water duct coil into my duct work.. would this not reduce the cfm's delivered by the air handler?

The hot water duct coil that I looked at (HWC1520) has a table that specifies at 3gpm (which would mean my using a 940-3 CV flow control valve) it would deliver 24'200 btuh with a water temperature of 120f at 800 cfm and 33'800 with a water temperature of 140f at 800cfm. What figure should I be using from the J load to calculate the size of the hot water duct coil? The Heating Loss BTUH, Latent Gain BTUH or the Sensible Gain BTUH?

Do I have to use the same manufacturer condenser as the air handler? I was thinking of buying one with a heat pump either to replace the existing or to purchase if I put in one of my new existing air handlers to compliment the 'mad scientist' approach of heating a large reservoir of water?

Some other factors that I should mention:

The current system that I have is a 3 zone 3.5 ton with 15kw heat pack and no heat pump.. I have to make a choice as to whether I replace the condenser outside with one that has a heat pump or rip out the existing 3.5 ton system and just condition the primary zone (the other zones are a tack room and studio that I can condition seperately - this would help me with cross charging energy costs too as right now I have no idea how much those rented spaces are costing to heat/cool). I have 4 air handlers sat around doing nothing (two of the aforementioned uhsl-hm2417ja and 2 of 1.5 ton with a duct coil in the air handler 18mbxb-hw First Company Products - First Operations, LP - Product Brochures / Data Sheets ) my idea was to take out the existing system (barely used) remove the zoning and put in a seperate system for the primary zone. The main supply and return duct would then be 'oversized' which could potentially accomodate for the water duct coil and the effect it would have on the cfm?

Many thanks for anybody that has the patience to read through this and many more thanks for anybody that helps me figure out what to do.

Old 12-03-10, 10:56 PM
Join Date: Aug 2010
Location: USA
Posts: 1
Received 0 Votes on 0 Posts
How about Hot Water duct coil addition to heat a mobile home?

I have no answer for you, but I've been researching new ways to heat my home. I have an older single-wide mobile home with an original Coleman 3400 Series heater. I have a heat pump that was installed later that is on the fritz. a replacement Heat pump and A-Coil for this setup is probably over $3000 (the old R-22 system has to be replaced).

I just had a brainstorm about replacing my hot water heater with a new hybrid unit for $1200-$1800, adding a hot water duct coil to my air handler by raising the existing unit the necessary 8 inches or less (to keep the water below the electrical connections and the motor) and use a heat pump hot water system to heat my home. I live in Portland, Oregon where the temperature seldom reaches the 20s. I would halve my hot water heating bill and I suspect would about halve my heating bill. I would still have the resistive heat elements available and working just like before if the temperature dropped too much.

I plan to re-roof this next year and really insulate it. My mother's double-wide home only has electric heat but typically runs less per month to heat than my single-wide. the only difference between her home and mine is that hers is 80% larger and has a really well insulated roof. She also uses less hot water having only one person home vs two. This last summer, while we suffered in the heat, her little window air conditioner (5000 btu) keeps her house very comfortable and is only needed on the hottest days, again attesting to her much better roof insulation. Our homes otherwise are from the same builder in the same year and have similar 2x4 exterior wall construction with aluminum siding and window frames. (We are slowly getting the windows replaced with new energy efficient ones.)

Besides heating the hot water and furnace, I'm thinking that by re-routing the return air through the water heater space in the summer, the heat pump becomes an air conditioner while heating the hot water. (Actually, if you could back up your refrigerator and freezer to the hot water heater, you could gain some more energy efficiency, though the heat pump on the water heater would still need some access to outside air in the summer when the house got too cool and during the winter to draw additional heat from outside. Hard to accomplish unless the water heater was next to the kitchen as it is in my mother's home. What about routing the dryer vent into the water heater closet where you could recover some of that lost heat in the winter when drying clothes.) Anyway, some interesting possibilities. It would be more difficult to achieve in a normal stick-built home unless it was built from the ground up.

I'd like to get some feedback on these ideas. Does anyone else think it is feasible? I can do most of the work myself to really save some dough. I've already rewired this place to bring it up to today's standards and beyond for my computers, shop tools, disposal, and dishwasher as well as adding GFCIs where needed for kitchen, bath, shop, and outdoors. I've already repaired and improved insulation under the house and fixed a lousy water heater replacement installation by a local plumbing shop, new flooring system, and repaired damaged particle board subfloor (should be outlawed, especially in mobile homes).
Old 12-04-10, 01:56 AM
airman.1994's Avatar
Join Date: Dec 2005
Location: VA
Posts: 5,795
Received 8 Votes on 8 Posts
Most of your ideas will have little to no pay back. A heat pump will be so much more efficient than the water heater. Dryer duct to water heater will be a killer for IAQ. Plus be a nightmare on the coil of the water heater.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: