crawlspace/radiators vs slab/radiant
I want to get some opinions on the cost of two options for a family room addition. The addition is for a ranch house with a full basement which happens to have its ground floor very close to grade. The house has radiators with 4 zones. We are located in the east near philadelphia, so it gets cold, but not extreme.
So the first option for the addition is crawlspace with another zone for the hotwater radiators. This seems the most straight forward but I would want to insulate and condition the crawlspace to prevent the floor from feeling cold underfoot. Its easier intoduce heat and ventilation air into the crawl space with a hot air system, in this case we don’t have that.
So the second option is using a slab on grade – again the floor is close to grade. A slab floor in our area feels cold in the winter so if we do a slab we would like to use radiant heat in the slab. The existing system is already zoned but I am wondering about the difficulty of tapping a radient system into a conventional convector system.
Which will cost more? By the time we trade off the joists and deck for a concrete slab will we have paid for most of the radiant system anyway?
Replies
Some things to consider IMHO, maybe you have already thought of these:
> You will need to do a heat loss calculation on the proposed addition to know if your current boiler will handle the capacity, and if not, the cost of upgrading or adding an additional heat source for radiant in-floor. Contrast any additional cost there against a forced air system that would both condition the crawl and heat the addition. If your current boiler DOES have excess capacity, it's a simple matter to bring the water temp/pressure etc to optimum for in-slab.
> Having radiant heat already, would you even be happy with forced air?
> Are you going to hire a GC for this project, or DIY GC? These would be good questions to pose to a qualified remodel GC type with a good track record in remodel/additions with significant HVAC re-work.
I know that the capacity of the existing system will have to come into the decision, and there will be a GC, and we will be able to get advice via their subcontractor, but in the meantime we are trying to gather info.
We could simply use forced air in this addition but the space is fairly open to the rest of the house and I have my doubts about the two systems working well together.
The one thing I neglected to mention is the owner desires carpet in the addition, and if carpet goes down on a slab it will most certainly need a pad which will work against radiant heating.
Got you, but I think it's going to be difficult learning how much each option is going to cost without factoring in where the costs are likely to come from'
Since you're just doing research at this point, why not add option 3...going with floor joist/subfloor/crawl space system, and still use hot water via tubes in the joist space (usually called "staple up") or between sleepers on top of the subfloor (usually called "sandwich"). This may allow you to leverage some value out of your current boiler/control system while also providing warm feet. There is even a product called WarmBoard I believe, that acts as both subfloor and in-floor heat, that compares well in cost with other radiant systems because the same crew can put down both sub-floor and in-floor heat in one step.
Try doing searches on "staple up" "WarmBoard" etc for more info.
As far as the carpet and pad go, if you use a fairly high density rubber pad, you may be able to transmit enough BTUs to heat the space comfortably with carpet, depending on the heat loss.
Edited 2/5/2004 3:18:53 PM ET by johnnyd
Thanks Johnnyd.
Does anybody else have a sense of the relative cost? Seems like I tossed this one into a black hole here!
As far as RFH tubes in slab versus RFH tubes in joist/subfloor system, almost for sure the slab would be less costly, simply because basic foundation work (fill, compaction, footings, etc ) would be about the same either way, and you'll have less labor cost in placing tubes in the slab. The slab (high mass) will respond to changes in heating demand more slowly than a suspended system (low mass) would, but there are lots of ways to compensate for that.
The costs to adapt your exisiting boiler to RFH, or add an addtional heat source, plus the manifold, air handler, valves, pumps etc would also be probably about the same.
So the delta would be the difference...in your area....between having a foundation/ crawl space wall/joist/subfloor built and a foundation/slab.
Roughly speaking of course, IMHO.
Edited 2/12/2004 10:25:31 AM ET by johnnyd
Ok, that makes sense when you compare to a radient system with the floor joists. But I was more concerned with comparing it to conventional radiators, with the consideration that we want to keep the crawlspace warm.
So that gets down to why you want a crawl space...just to keep the floor warm? Or is there an addiitonal benefit of flexibility in adding post-construction plumbing and wiring?
I think if you look at it, you'll be better off with tubes in a slab. Unless you also want to air condition the new space.
Well, not quite - there is no preference for a crawlspace, rather I'm just trying to determine the least expensive approach. We won't do something that creates a cold floor whether slab or crawlspace. If we do a slab it will be radiant heat or radiators and electric resistance in the slab. If we do a crawl space it will be conditioned so that the floor is not cold.
Air conditioning is likely in the mix whatever is done, but we will not go to hot air heat because I don't believe it will be satisfactory while the rest of the house is on radiators - the new space is going to be wide open to the existing house and the systems behave too differently.
I am leaning towards one of the slab solutions right now.
Let me know how it comes out. I've done RFH in a workshop slab, and am designing a low mass RFH system for a 1600 sq ft house, most of it is over a crawl space.
Try this site for more advice. Lottsa hydronic/radiant experts there.
http://www.heatinghelp.com/wall_forum.cfm