How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Phil Your Own Question
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8768
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
Type Your HVAC Question Here...
Phil is online now
A new question is answered every 9 seconds

Hello All! I am currently replacing my heating system. I plan

This answer was rated:

Hello All! I am currently replacing my heating system. I plan to install a 4 zone radiant heat and domestic hot water off of an unpurchsed tankless water heater. What I would like to do is run 4 zones. Two zones on the first floor with PEX radiant heat and then one zone on the second floor with baseboard and one zone in basement also with baseboard.

First floor: PEX 1/2" radiant heat ran through floor joists
Zone 1- Living room, Dining room, Foyer, and Kitchen (781 sf total)
Zone 2- (2) Bedrooms, Bathroom, and hallway

Second Floor: baseboard
Bedroom (326 sf) and Nursery/Hall (100 sf) 426 sf total

Basement: baseboard
Laundry (110), Hallway (36), and Family Room (234) 380 sf total

I am very confident that I can install all the Pex and baseboard, my only concerns are running the two different types off of one heat source. Pretty sure baseboard is hotter than radiant.

What water heater should I get? I am looking at Takagi T-D2-IN but fear it may be an overkill

What pumps should I get? I have been looking at the Taco pumps, but don't know what size to get. Different for each zone size? i would assume

What controls the pumps. I know obviously a thermostat, but saw something about a zone relay controller or something.

And last for now; I have been doing a lot of research, and i have seen a few different set ups. most are similar, but some call for an expansion tank. I don't see the need in an open system. Either way i have a fairly new one from my previous, closed, oil fueled, radiator system.

It is starting to get cold, and my pregnant wife is being very patient. I am starting to pipe the gas in tomorrow and want to get everything i need. I would appreciate any help, even if just links to better guides.

I am looking for a detailed plan to put this together right the first time. I would appreciate any recommendations as far as products and/or suggestions. I have nothing at the moment, other than electric baseboards in the 2nd floor bedroom.

I also considered putting in forced hot air instead of the water. Mainly for the ease if putting in central air in the future. Just didn't want to lose the head room in the basement; only 7' as it is.

Thank you in advance!
Welcome to Just Answer!

We can start with some preliminary remarks and get into as much detail as you need later.

Tell me a bit about the house construction, insulation, and locality, (nearest city) please... tell me the BTU output rating stamped on the existing hot water heater or furnace and tell me if it runs all the time in cold weather or not. I can assess the size and type of the boiler required that way.

Beyond that Taco makes good, cost effective equipment. If you buy their packaged 4 zone system complete with the 'Taco relay' and thermostats. Couple it with the smallest pumps they offer, it will come complete with full instructions, piping and wiring diagram. Run the boiler at 160F to accommodate the base board heaters.

These are virtually all closed loop systems for a range of reasons, if we go with a closed loop system you will need a 2 gallon expansion tank.

Use a *mixing valve* (thats a 3 way valve that we can discuss later) .. fit down stream of the pump for the radiant heat floor zone in order to hold the radiant floor loop at 120F... then run the system... if the pump cycles more than 3 times an hour, set the mixing valve to mix the water that goes into the radiant floor loop at 110F.

Thats the simplest way to do to it.

If you want a much more complex system you can use an outside master thermostat and other controls to reset the hot water temperature according the outside temperature. This approach will save on operating costs marginally but will run up the first costs and the ongoing maintenance and service costs due to its complexity. I would recommend that option if you are in a severe climate, but not in a mild climate.

If you want that option I will have to investigate its viability with the Tagaki water heater.. those controls get involved, in that case the Tagaki may not be your best choice.. I can make a recommendation on that as we go along.

Let me know in detail on all of those issues, we can go from there.

Note: I am currently traveling and may only be able to respond once a day... if that is OK with you let me know, if not, I can opt out so other of our experts here can respond.

Customer: replied 3 years ago.

Phil, thank you for responding. I am located near Hartford, CT. I just bought my home in May and my oil burner died a week into living here. I do not know the efficiency of the boiler. I googled the model # XXXXX it ironically linked me back to you when looking for the btu rating. Another poster mentioned it was 141,000 btus, but i don't know how reliable the source is. the model # XXXXX XXXXX Assuming that the btus were properly sized, we still have the issue of added two additional floors. The basement was unfinished, and the 2nd floor has electric baseboard. Not sure if this helps. The insulation on the first floor is most likely poor to fair, at best. The 2nd floor is good, blown-in insulation, and the basement will be good; i plan to put R-15 on the exterior walls.


As far as the open or closed system, I am not impartial to either, just thought the open, or direct, was more economical. Seemed that i would need multiple water heaters/boilers.


I work 6 days a week and only have sunday's and evenings to get this done. Responses once a day works for me as long as I have something to run with on my down time.


It's getting late and i'm getting delirious. We will talk again soon. No rush on responding tonite.


Thanks again,



Hello again, thanks for the information.

The Takagi T-D2- indoor or outdoor style is variable firing, so that it will not be too large for your job, and it will be able to provide hot water suitable for two people taking showers at a time, even while running the dishwasher etc in most cases. That unit however is NOT a 'combination unit' however... that means with two separate heat exchangers inside, one for domestic hot water production and one for central heat. Takagi's claim that it can be used for space heating or domestic hot water can be a bit confusing.


You would need one Takagi for space heat, and another one for domestic hot water heat.

CLICK HERE FOR THE MANUAL..we can discuss the details later. Your gas meter may not be large enough to support that gas flow and may have to be changed, depending on what other gas appliances you have in the house.

As wonderful as these new instant hot water heaters are, consumer reports magazine cautions against them in many applications, due to the complexity (especially with variable firing rate units as the T-D2).. life span that seems to average out at 10 years, with expensive repairs required in the meantime.


There are 'combi' water heaters on the market that can do both space heating and domestic hot water heating. Not my favorite approach but they are common.


Click on that link. it should work


It will be easy to mess this up, especially if you are in a rush and with cold weather coming on and a pregnant wife.

It will pay us to slow things up. These systems are not 'plug and play' so to speak, there are a very wide range of issues. Your mention of a ducted system so that you can add central air conditioning later raises many more issues.

For now it will be smart to discuss the details of the existing burnham boiler failure for at least a few minutes...those are some of the most reliable boilers on the market... for now at least it may be a good idea to consider repairing it, depending on how it failed... or replacing it directly with a new Burnham boiler.. those can be purchased with natural gas or oil burners in them (they are interchangeable).

That burnham boiler historically will last 25 to 30 years... and outlast 3 or 4 of the tankless varieties, including the Takagi, even though the Takagi is one of the best.

Fixing the burnham if that turns out to be viable will take the pressure off of you so that you can make the most optimal decision later.... we owe it to ourselves to at least discuss that.


Regarding insulating the basement. Thats tricky business to say the least. There are materials and vapor barrier issues to consider in order to avoid moisture and mold conditions behind the insulated walls... depending on the soil conditions and drainage on the outside the house against the basement walls there can be problems that do not show up with the walls un-insulated... that once insulated, can turn into mold and dry rot breeding areas.

What you want to do regarding the basement and heating the house needs to be considered in those contexts if you want a reliable job. It will not be a bad idea at all to have some on site assistance designing the plumbing connections and 3 way mixing valve installation needed for the floor heating loop, site variables are too complex to effectively address without seeing the job.

Let me know about the old boilers failure mode.

We can go from there.


Customer: replied 3 years ago.

The boiler would just turn off and a light would come on. I opened the cover and hit the reset button, which would fire it up for less than a minute and then turn off again. To no avail, I called the company that had been servicing the burner prior to my ownership. I was told only that they have had nothing but problems with it and the previous owner didn't want to fix the part that needed fixing. They were very vague and told me any other details were confidential.


I think I mentioned that I have already removed the cast iron radiators that were throughout the home. If you think this may be worth fixing, I could have someone take a look at it. Not sure if they would be able to diagnose any problem while it is disconnected though.


Are you saying that the Burnham could be converted to NG or that the new ones are? If this one could be converted and fixed, I would consider it, if it made more sense.


As far as the meter not giving enough gas, that shouldn't be an issue. I still need them to put the meter in. The gas is ran to the house. I am piping everything and then the meter will be installed. If we decide to go that route I will inform them of the needs.


Insulating and finishing the basement is not top priority now. I understand about the moisture barriers and whatnot. I had a building inspector here earlier in the week.


I didn't mean to scare you about the duct work for central air; if I go the route we are going, I would nix that option and keep the window shakers or put a split system in.


Let me know what you think. The ideas I have thrown at you were all my attempt at being economical.


Let me know what you think.






Hello again Shawn,

The boiler service company that told you the details of the failure were confidential is way off base... what failed is part of any decent diagnosis and report.. The contractors behavior in this matter does not speak well for them.... that may be why they had a lot of trouble with the system.

Let me know if you need help finding a competent boiler service contractor in your area.

If the boiler was not leaking water, the problem is generally easily fixable within the oil burner assembly... it could be minor adjustments, that is most common... repairs of that nature generally cost 300 to 400 dollars.

A complete new burner head wholesales for under 500 dollars.. installed its worth $1,000. its a two hour job including flue gas analysis.


You can install base board hot water heat, and under floor radiant heat using that boiler, but there has to be some on site assistance arranging a mixing valve to keep the floor radiant heat around 120F as the base boards run 160F... see my first response on that issue.

You need a competent hydronic heating contractor to assist you with that, none of this is work most laymen can do themselves... the entire lay out has to be seen in detail to design the pipe and controls correctly... A taco system, with the taco pumps and relay will work well however.

Tell me please how domestic hot water is being produced. Is there a heat exchanger with boiler steam or hot water going through two pipes on the heat exchanger and city water coming into the heat exchanger on one end and hot water coming out the other end that goes to the hot water taps and shower in the house?

We can go from there.


Customer: replied 3 years ago.

I will try to find a reliable contractor to handle the details and set me up. Right now the domestic water is coming from an electric water heater I installed the night that the boiler died. However I have a feeling you were referring to the Burnham... In which case I'm not sure.

screen capture windows 7

screen capture program


not sure if i did that right, but those are two pictures of where the pipes enter and exit. Let me know if this is what you were asking.

Hello again, thanks for the pictures, those show the heat exchanger that used to be attached to the boiler to make domestic hot water.

Since you are not using the water heater to heat domestic hot water, you will get by just fine with a simpler Takagi water heater, rated at 80,000 to 120,000 btu hour output. Leave the existing electric base boards on the second floor in place for back up heat. (sooner or later the Takagi heater will fail, you will be glad you kept the back up)


80,000 btu/hr will handle the load in most cases if the 3 story space is under 1,500 square feet... if the space is close to 2,500 square feet you will need the larger unit... in order to be exact a full load calculation on the house is required (and required by law, according to Title 24 energy code)

From here on it will best to stay with the new electric water heater that you just installed to provide domestic hot water.

You can use either the takagi instant water heater for space heating, and a 3 way valve mixing valve ahead of the radiant floor piping inlet to keep the temperature at 120 F... or you can use the existing boiler after it is repaired (with the mixing valve fit for the radiant floor loop)

Pipe the rest to suit which ever Taco hydronic heating package you select with the help of a hydronic heating contractor, if he sells you the package he should be happy to look the job over and show you how to connect it all. See my initial remarks on that topic.

click here.

Look at the 4 zone relay diagram, and select the smallest pump they sell for each zone... the room thermostats in each zone control the pumps.

The piping has to be installed so that it does not trap air in the high points, thats where you need a hydronics heating man to examine your situation and advise on the pipe routing and location of the air bleeds.

Many hydronics specialist companies sell the complete package you just mount it on the wall and connect the piping....that would be the way to go in this case.

Let me know if you need help locating such a vendor in your area.

We can go from there.


See my previous post please, 1 minute earlier than this one.

Alternative Heating & Supplies XXXXX Oxford, CT ‎ (NNN) NNN-NNNN ‎ · "Radiant Pex Tubing; Radiant Manifolds; Radiant Controls; Radiant floor designs DIY; Pex Tools; Pex Fittings. Heat Exchangers. 5 x 12 Brazed Plate Heat ..." -

Stay in touch as needed, if you rate my service so far positively I will hold the question open for any follow up you might need.


Phil and other HVAC Specialists are ready to help you
Hello again, thanks for the positive rating.

You will be smart to tell the people you buy the pump manifold from to stop by your house and look the job over so they can build the manifold to fit.... and.... make a sketch of how to connect it all. If they want $100 or so to do that for you, it will be well worth it.

Buy everything for the entire job from them, the pump manifold, tubing, thermostat, taco relay..... and the complete plans....make sure you talk to one of their most competent people... that way you can go back to them if there is any problem and they will be obligated to make it all work. Thats critical information.

Good luck,

I am traveling for the next few weeks I will check in every day or so to see if you have posted.